Network Working Group                                        P. Holbrook
Request for Comments:  1244                                       CICNet
FYI: 8                                                       J. Reynolds
                                                               July 1991

                         Site Security Handbook

Status of this Memo

   This handbook is the product of the Site Security Policy Handbook
   Working Group (SSPHWG), a combined effort of the Security Area and
   User Services Area of the Internet Engineering Task Force (IETF).
   This FYI RFC provides information for the Internet community.  It
   does not specify an Internet standard.  Distribution of this memo is

Contributing Authors

   The following are the authors of the Site Security Handbook.  Without
   their dedication, this handbook would not have been possible.

   Dave Curry (Purdue University), Sean Kirkpatrick (Unisys), Tom
   Longstaff (LLNL), Greg Hollingsworth (Johns Hopkins University),
   Jeffrey Carpenter (University of Pittsburgh), Barbara Fraser (CERT),
   Fred Ostapik (SRI NISC), Allen Sturtevant (LLNL), Dan Long (BBN), Jim
   Duncan (Pennsylvania State University), and Frank Byrum (DEC).

Editors' Note

   This FYI RFC is a first attempt at providing Internet users guidance
   on how to deal with security issues in the Internet.  As such, this
   document is necessarily incomplete.  There are some clear shortfalls;
   for example, this document focuses mostly on resources available in
   the United States.  In the spirit of the Internet's "Request for
   Comments" series of notes, we encourage feedback from users of this
   handbook.  In particular, those who utilize this document to craft
   their own policies and procedures.

   This handbook is meant to be a starting place for further research
   and should be viewed as a useful resource, but not the final
   authority.  Different organizations and jurisdictions will have
   different resources and rules.  Talk to your local organizations,
   consult an informed lawyer, or consult with local and national law
   enforcement.  These groups can help fill in the gaps that this
   document cannot hope to cover.

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   Finally, we intend for this FYI RFC to grow and evolve.  Please send
   comments and suggestions to:

Table of Contents

1.  Introduction.....................................................  3
1.1  Purpose of this Work............................................  3
1.2  Audience........................................................  3
1.3  Definitions.....................................................  4
1.4  Related Work....................................................  4
1.5  Scope...........................................................  4
1.6  Why Do We Need Security Policies and Procedures?................  5
1.7  Basic Approach..................................................  7
1.8  Organization of this Document...................................  7
2.  Establishing Official Site Policy on Computer Security...........  9
2.1  Brief Overview..................................................  9
2.2  Risk Assessment................................................. 10
2.3  Policy Issues................................................... 13
2.4  What Happens When the Policy Is Violated........................ 19
2.5  Locking In or Out............................................... 21
2.6  Interpreting the Policy......................................... 23
2.7  Publicizing the Policy.......................................... 23
3.  Establishing Procedures to Prevent Security Problems............. 24
3.1  Security Policy Defines What Needs to be Protected.............. 24
3.2  Identifing Possible Problems.................................... 24
3.3  Choose Controls to Protect Assets in a Cost-Effective Way....... 26
3.4  Use Multiple Strategies to Protect Assets....................... 26
3.5  Physical Security............................................... 27
3.6  Procedures to Recognize Unauthorized Activity................... 27
3.7  Define Actions to Take When Unauthorized Activity is Suspected.. 29
3.8  Communicating Security Policy................................... 30
3.9  Resources to Prevent Security Breaches.......................... 34
4.  Types of Security Procedures..................................... 56
4.1  System Security Audits.......................................... 56
4.2  Account Management Procedures................................... 57
4.3  Password Management Procedures.................................. 57
4.4  Configuration Management Procedures............................. 60
5.  Incident Handling................................................ 61
5.1  Overview........................................................ 61
5.2  Evaluation...................................................... 65
5.3  Possible Types of Notification.................................. 67
5.4  Response........................................................ 71
5.5  Legal/Investigative............................................. 73
5.6  Documentation Logs.............................................. 77
6.  Establishing Post-Incident Procedures............................ 78
6.1  Overview........................................................ 78
6.2  Removing Vulnerabilities........................................ 78
6.3  Capturing Lessons Learned....................................... 80

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6.4  Upgrading Policies and Procedures............................... 81
7.  References....................................................... 81
8.  Annotated Bibliography........................................... 83
8.1  Computer Law.................................................... 84
8.2  Computer Security............................................... 85
8.3  Ethics.......................................................... 91
8.4  The Internet Worm............................................... 93
8.5  National Computer Security Center (NCSC)........................ 95
8.6  Security Checklists............................................. 99
8.7  Additional Publications......................................... 99
9.  Acknlowledgements................................................101
10.  Security Considerations.........................................101
11.  Authors' Addresses..............................................101

1.  Introduction

1.1  Purpose of this Work

   This handbook is a guide to setting computer security policies and
   procedures for sites that have systems on the Internet.  This guide
   lists issues and factors that a site must consider when setting their
   own policies.  It makes some recommendations and gives discussions of
   relevant areas.

   This guide is only a framework for setting security policies and
   procedures.  In order to have an effective set of policies and
   procedures, a site will have to make many decisions, gain agreement,
   and then communicate and implement the policies.

1.2  Audience

   The audience for this work are system administrators and decision
   makers (who are more traditionally called "administrators" or "middle
   management") at sites.  This document is not directed at programmers
   or those trying to create secure programs or systems.  The focus of
   this document is on the policies and procedures that need to be in
   place to support any technical security features that a site may be

   The primary audience for this work are sites that are members of the
   Internet community.  However, this document should be useful to any
   site that allows communication with other sites.  As a general guide
   to security policies, this document may also be useful to sites with
   isolated systems.

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1.3  Definitions

   For the purposes of this guide, a "site" is any organization that
   owns computers or network-related resources.  These resources may
   include host computers that users use, routers, terminal servers,
   PC's or other devices that have access to the Internet.  A site may
   be a end user of Internet services or a service provider such as a
   regional network.  However, most of the focus of this guide is on
   those end users of Internet services.

   We assume that the site has the ability to set policies and
   procedures for itself with the concurrence and support from those who
   actually own the resources.

   The "Internet" is those set of networks and machines that use the
   TCP/IP protocol suite, connected through gateways, and sharing a
   common name and address spaces [1].

   The term "system administrator" is used to cover all those who are
   responsible for the day-to-day operation of resources.  This may be a
   number of individuals or an organization.

   The term "decision maker" refers to those people at a site who set or
   approve policy.  These are often (but not always) the people who own
   the resources.

1.4  Related Work

   The IETF Security Policy Working Group (SPWG) is working on a set of
   recommended security policy guidelines for the Internet [23].  These
   guidelines may be adopted as policy by regional networks or owners of
   other resources.  This handbook should be a useful tool to help sites
   implement those policies as desired or required.  However, even
   implementing the proposed policies isn't enough to secure a site.
   The proposed Internet policies deal only with network access
   security.  It says nothing about how sites should deal with local
   security issues.

1.5  Scope

   This document covers issues about what a computer security policy
   should contain, what kinds of procedures are need to enforce
   security, and some recommendations about how to deal with the
   problem.  When developing a security policy, close attention should
   be made not only on the security needs and requirements of the local
   network, but also the security needs and requirements of the other
   interconnected networks.

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   This is not a cookbook for computer security.  Each site has
   different needs; the security needs of a corporation might well be
   different than the security needs of an academic institution.  Any
   security plan has to conform to the needs and culture of the site.

   This handbook does not cover details of how to do risk assessment,
   contingency planning, or physical security.  These things are
   essential in setting and implementing effective security policy, but
   this document leaves treatment of those issues to other documents.
   We will try to provide some pointers in that direction.

   This document also doesn't talk about how to design or implement
   secure systems or programs.

1.6  Why Do We Need Security Policies and Procedures?

   For most sites, the interest in computer security is proportional to
   the perception of risk and threats.

   The world of computers has changed dramatically over the past
   twenty-five years.  Twenty-five years ago, most computers were
   centralized and managed by data centers.  Computers were kept in
   locked rooms and staffs of people made sure they were carefully
   managed and physically secured.  Links outside a site were unusual.
   Computer security threats were rare, and were basically concerned
   with insiders: authorized users misusing accounts, theft and
   vandalism, and so forth.  These threats were well understood and
   dealt with using standard techniques: computers behind locked doors,
   and accounting for all resources.

   Computing in the 1990's is radically different.  Many systems are in
   private offices and labs, often managed by individuals or persons
   employed outside a computer center.  Many systems are connected into
   the Internet, and from there around the world: the United States,
   Europe, Asia, and Australia are all connected together.

   Security threats are different today.  The time honored advice says
   "don't write your password down and put it in your desk" lest someone
   find it.  With world-wide Internet connections, someone could get
   into your system from the other side of the world and steal your
   password in the middle of the night when your building is locked up.
   Viruses and worms can be passed from machine to machine.  The
   Internet allows the electronic equivalent of the thief who looks for
   open windows and doors; now a person can check hundreds of machines
   for vulnerabilities in a few hours.

   System administrators and decision makers have to understand the
   security threats that exist, what the risk and cost of a problem

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   would be, and what kind of action they want to take (if any) to
   prevent and respond to security threats.

   As an illustration of some of the issues that need to be dealt with
   in security problems, consider the following scenarios (thanks to
   Russell Brand [2, BRAND] for these):

      - A system programmer gets a call reporting that a
        major underground cracker newsletter is being
        distributed from the administrative machine at his
        center to five thousand sites in the US and
        Western Europe.

        Eight weeks later, the authorities call to inform
        you the information in one of these newsletters
        was used to disable "911" in a major city for
        five hours.

      - A user calls in to report that he can't login to his
        account at 3 o'clock in the morning on a Saturday.  The
        system staffer can't login either.  After rebooting to
        single user mode, he finds that password file is empty.
        By Monday morning, your staff determines that a number
        of privileged file transfers took place between this
        machine and a local university.

        Tuesday morning a copy of the deleted password file is
        found on the university machine along with password
        files for a dozen other machines.

        A week later you find that your system initialization
        files had been altered in a hostile fashion.

      - You receive a call saying that a breakin to a government
        lab occurred from one of your center's machines.  You
        are requested to provide accounting files to help
        trackdown the attacker.

        A week later you are given a list of machines at your
        site that have been broken into.

       - A reporter calls up asking about the breakin at your
         center.  You haven't heard of any such breakin.

        Three days later, you learn that there was a breakin.
        The center director had his wife's name as a password.

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      - A change in system binaries is detected.

        The day that it is corrected, they again are changed.
        This repeats itself for some weeks.

      - If an intruder is found on your system, should you
        leave the system open to monitor the situation or should
        you close down the holes and open them up again later?

      - If an intruder is using your site, should you call law
        enforcement?  Who makes that decision?  If law enforcement asks
        you to leave your site open, who makes that decision?

      - What steps should be taken if another site calls you and says
        they see activity coming from an account on your system?  What
        if the account is owned by a local manager?

1.7  Basic Approach

   Setting security policies and procedures really means developing a
   plan for how to deal with computer security.  One way to approach
   this task is suggested by Fites, et. al. [3, FITES]:

      -  Look at what you are trying to protect.
      -  Look at what you need to protect it from.
      -  Determine how likely the threats are.
      -  Implement measures which will protect your assets in a
         cost-effective manner.
      -  Review the process continuously, and improve things every time
         a weakness is found.

   This handbook will concentrate mostly on the last two steps, but the
   first three are critically important to making effective decisions
   about security.  One old truism in security is that the cost of
   protecting yourself against a threat should be less than the cost
   recovering if the threat were to strike you.  Without reasonable
   knowledge of what you are protecting and what the likely threats are,
   following this rule could be difficult.

1.8  Organization of this Document

   This document is organized into seven parts in addition to this

   The basic form of each section is to discuss issues that a site might
   want to consider in creating a computer security policy and setting
   procedures to implement that policy.  In some cases, possible options
   are discussed along with the some of the ramifications of those

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   choices.  As far as possible, this document tries not to dictate the
   choices a site should make, since these depend on local
   circumstances.  Some of the issues brought up may not apply to all
   sites.  Nonetheless, all sites should at least consider the issues
   brought up here to ensure that they do not miss some important area.

   The overall flow of the document is to discuss policy issues followed
   by the issues that come up in creating procedures to implement the

   Section 2 discusses setting official site policies for access to
   computing resources.  It also goes into the issue of what happens
   when the policy is violated.  The policies will drive the procedures
   that need to be created, so decision makers will need to make choices
   about policies before many of the procedural issues in following
   sections can be dealt with.  A key part of creating policies is doing
   some kind of risk assessment to decide what really needs to be
   protected and the level of resources that should be applied to
   protect them.

   Once policies are in place, procedures to prevent future security
   problems should be established.  Section 3 defines and suggests
   actions to take when unauthorized activity is suspected.  Resources
   to prevent secruity breaches are also discussed.

   Section 4 discusses types of procedures to prevent security problems.
   Prevention is a key to security; as an example, the Computer
   Emergency Response Team/Coordination Center (CERT/CC) at Carnegie-
   Mellon University (CMU) estimates that 80% or more of the problems
   they see have to do with poorly chosen passwords.

   Section 5 discusses incident handling: what kinds of issues does a
   site face when someone violates the security policy.  Many decisions
   will have to made on the spot as the incident occurs, but many of the
   options and issues can be discussed in advance.  At very least,
   responsibilities and methods of communication can be established
   before an incident.  Again, the choices here are influenced by the
   policies discussed in section 2.

   Section 6 deals with what happens after a security violation has been
   dealt with.  Security planning is an on-going cycle; just after an
   incident has occurred is an excellent opportunity to improve policies
   and procedures.

   The rest of the document provides references and an annotated

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2.  Establishing Official Site Policy on Computer Security

2.1  Brief Overview

   2.1.1  Organization Issues

      The goal in developing an official site policy on computer
      security is to define the organization's expectations of proper
      computer and network use and to define procedures to prevent and
      respond to security incidents.  In order to do this, aspects of
      the particular organization must be considered.

      First, the goals and direction of the organization should be
      considered.  For example, a military base may have very different
      security concerns from a those of a university.

      Second, the site security policy developed must conform to
      existing policies, rules, regulations and laws that the
      organization is subject to.  Therefore it will be necessary to
      identify these and take them into consideration while developing
      the policy.

      Third, unless the local network is completely isolated and
      standalone, it is necessary to consider security implications in a
      more global context.  The policy should address the issues when
      local security problems develop as a result of a remote site as
      well as when problems occur on remote systems as a result of a
      local host or user.

   2.1.2  Who Makes the Policy?

      Policy creation must be a joint effort by technical personnel, who
      understand the full ramifications of the proposed policy and the
      implementation of the policy, and by decision makers who have the
      power to enforce the policy.  A policy which is neither
      implementable nor enforceable is useless.

      Since a computer security policy can affect everyone in an
      organization, it is worth taking some care to make sure you have
      the right level of authority in on the policy decisions.  Though a
      particular group (such as a campus information services group) may
      have responsibility for enforcing a policy, an even higher group
      may have to support and approve the policy.

   2.1.3  Who is Involved?

      Establishing a site policy has the potential for involving every
      computer user at the site in a variety of ways.  Computer users

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      may be responsible for personal password administration.  Systems
      managers are obligated to fix security holes and to oversee the

      It is critical to get the right set of people involved at the
      start of the process.  There may already be groups concerned with
      security who would consider a computer security policy to be their
      area.  Some of the types of groups that might be involved include
      auditing/control, organizations that deal with physical security,
      campus information systems groups, and so forth.  Asking these
      types of groups to "buy in" from the start can help facilitate the
      acceptance of the policy.

   2.1.4  Responsibilities

      A key element of a computer security policy is making sure
      everyone knows their own responsibility for maintaining security.
      A computer security policy cannot anticipate all possibilities;
      however, it can ensure that each kind of problem does have someone
      assigned to deal with it.

      There may be levels of responsibility associated with a policy on
      computer security.  At one level, each user of a computing
      resource may have a responsibility to protect his account.  A user
      who allows his account to be compromised increases the chances of
      compromising other accounts or resources.

      System managers may form another responsibility level: they must
      help to ensure the security of the computer system.  Network
      managers may reside at yet another level.

2.2  Risk Assessment

   2.2.1  General Discussion

      One of the most important reasons for creating a computer security
      policy is to ensure that efforts spent on security yield cost
      effective benefits.  Although this may seem obvious, it is
      possible to be mislead about where the effort is needed.  As an
      example, there is a great deal of publicity about intruders on
      computers systems; yet most surveys of computer security show that
      for most organizations, the actual loss from "insiders" is much

      Risk analysis involves determining what you need to protect, what
      you need to protect it from, and how to protect it.  Is is the
      process of examining all of your risks, and ranking those risks by
      level of severity.  This process involves making cost-effective

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      decisions on what you want to protect.  The old security adage
      says that you should not spend more to protect something than it
      is actually worth.

      A full treatment of risk analysis is outside the scope of this
      document.  [3, FITES] and [16, PFLEEGER] provide introductions to
      this topic.  However, there are two elements of a risk analysis
      that will be briefly covered in the next two sections:

         1. Identifying the assets
         2. Identifying the threats

      For each asset, the basic goals of security are availability,
      confidentiality, and integrity.  Each threat should be examined
      with an eye to how the threat could affect these areas.

   2.2.2  Identifying the Assets

      One step in a risk analysis is to identify all the things that
      need to be protected.  Some things are obvious, like all the
      various pieces of hardware, but some are overlooked, such as the
      people who actually use the systems. The essential point is to
      list all things that could be affected by a security problem.

      One list of categories is suggested by Pfleeger [16, PFLEEGER,
      page 459]; this list is adapted from that source:

         1. Hardware: cpus, boards, keyboards, terminals,
            workstations, personal computers, printers, disk
            drives, communication lines, terminal servers, routers.

         2. Software: source programs, object programs,
            utilities, diagnostic programs, operating systems,
            communication programs.

         3. Data: during execution, stored on-line, archived off-line,
            backups, audit logs, databases, in transit over
            communication media.

         4. People: users, people needed to run systems.

         5. Documentation: on programs, hardware, systems, local
            administrative procedures.

         6. Supplies: paper, forms, ribbons, magnetic media.

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   2.2.3  Identifying the Threats

      Once the assets requiring protection are identified, it is
      necessary to identify threats to those assests.  The threats can
      then be examined to determine what potential for loss exists.  It
      helps to consider from what threats you are trying to protect your

      The following sections describe a few of the possible threats.  Unauthorized Access

         A common threat that concerns many sites is unauthorized access
         to computing facilities.  Unauthorized access takes many forms.
         One means of unauthorized access is the use of another user's
         account to gain access to a system.  The use of any computer
         resource without prior permission may be considered
         unauthorized access to computing facilities.

         The seriousness of an unauthorized access will vary from site
         to site.  For some sites, the mere act of granting access to an
         unauthorized user may cause irreparable harm by negative media
         coverage.  For other sites, an unauthorized access opens the
         door to other security threats.  In addition, some sites may be
         more frequent targets than others; hence the risk from
         unauthorized access will vary from site to site.  The Computer
         Emergency Response Team (CERT - see section has
         observed that well-known universities, government sites, and
         military sites seem to attract more intruders.  Disclosure of Information

         Another common threat is disclosure of information.  Determine
         the value or sensitivity of the information stored on your
         computers.  Disclosure of a password file might allow for
         future unauthorized accesses.  A glimpse of a proposal may give
         a competitor an unfair advantage.  A technical paper may
         contain years of valuable research.  Denial of Service

         Computers and networks provide valuable services to their
         users.  Many people rely on these services in order to perform
         their jobs efficiently.  When these services are not available
         when called upon, a loss in productivity results.

         Denial of service comes in many forms and might affect users in
         a number of ways.  A network may be rendered unusable by a

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         rogue packet, jamming, or by a disabled network component.  A
         virus might slow down or cripple a computer system.  Each site
         should determine which services are essential, and for each of
         these services determine the affect to the site if that service
         were to become disabled.

2.3  Policy Issues

   There are a number of issues that must be addressed when developing a
   security policy.  These are:

      1.  Who is allowed to use the resources?
      2.  What is the proper use of the resources?
      3.  Who is authorized to grant access and approve usage?
      4.  Who may have system administration privileges?
      5.  What are the user's rights and responsibilities?
      6.  What are the rights and responsibilities of the
          system administrator vs. those of the user?
      7.  What do you do with sensitive information?

   These issues will be discussed below.  In addition you may wish to
   include a section in your policy concerning ethical use of computing
   resources.  Parker, Swope and Baker [17, PARKER90] and Forester and
   Morrison [18, FORESTER] are two useful references that address
   ethical issues.

   2.3.1  Who is Allowed to use the Resources?

      One step you must take in developing your security policy is
      defining who is allowed to use your system and services.  The
      policy should explicitly state who is authorized to use what

   2.3.2  What is the Proper Use of the Resources?

      After determining who is allowed access to system resources it is
      necessary to provide guidelines for the acceptable use of the
      resources.  You may have different guidelines for different types
      of users (i.e., students, faculty, external users).  The policy
      should state what is acceptable use as well as unacceptable use.
      It should also include types of use that may be restricted.

      Define limits to access and authority.  You will need to consider
      the level of access various users will have and what resources
      will be available or restricted to various groups of people.

      Your acceptable use policy should clearly state that individual
      users are responsible for their actions.  Their responsibility

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      exists regardless of the security mechanisms that are in place.
      It should be clearly stated that breaking into accounts or
      bypassing security is not permitted.

      The following points should be covered when developing an
      acceptable use policy:

         o Is breaking into accounts permitted?
         o Is cracking passwords permitted?
         o Is disrupting service permitted?
         o Should users assume that a file being world-readable
           grants them the authorization to read it?
         o Should users be permitted to modify files that are
           not their own even if they happen to have write
         o Should users share accounts?

      The answer to most of these questions will be "no".

      You may wish to incorporate a statement in your policies
      concerning copyrighted and licensed software.  Licensing
      agreements with vendors may require some sort of effort on your
      part to ensure that the license is not violated.  In addition, you
      may wish to inform users that the copying of copyrighted software
      may be a violation of the copyright laws, and is not permitted.

      Specifically concerning copyrighted and/or licensed software, you
      may wish to include the following information:

         o Copyrighted and licensed software may not be duplicated
           unless it is explicitly stated that you may do so.
         o Methods of conveying information on the
           copyright/licensed status of software.
         o When in doubt, DON'T COPY.

      Your acceptable use policy is very important.  A policy which does
      not clearly state what is not permitted may leave you unable to
      prove that a user violated policy.

      There are exception cases like tiger teams and users or
      administrators wishing for "licenses to hack" -- you may face the
      situation where users will want to "hack" on your services for
      security research purposes.  You should develop a policy that will
      determine whether you will permit this type of research on your
      services and if so, what your guidelines for such research will

      Points you may wish to cover in this area:

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         o Whether it is permitted at all.
         o What type of activity is permitted: breaking in, releasing
           worms, releasing viruses, etc..
         o What type of controls must be in place to ensure that it
           does not get out of control (e.g., separate a segment of
           your network for these tests).
         o How you will protect other users from being victims of
           these activities, including external users and networks.
         o The process for obtaining permission to conduct these

      In cases where you do permit these activities, you should isolate
      the portions of the network that are being tested from your main
      network.  Worms and viruses should never be released on a live

      You may also wish to employ, contract, or otherwise solicit one or
      more people or organizations to evaluate the security of your
      services, of which may include "hacking".  You may wish to provide
      for this in your policy.

   2.3.3  Who Is Authorized to Grant Access and Approve Usage?

      Your policy should state who is authorized to grant access to your
      services.  Further, it must be determined what type of access they
      are permitted to give.  If you do not have control over who is
      granted access to your system, you will not have control over who
      is using your system.  Controlling who has the authorization to
      grant access will also enable you to know who was or was not
      granting access if problems develop later.

      There are many schemes that can be developed to control the
      distribution of access to your services.  The following are the
      factors that you must consider when determining who will
      distribute access to your services:

         o Will you be distributing access from a centralized
           point or at various points?

      You can have a centralized distribution point to a distributed
      system where various sites or departments independently authorize
      access.  The trade off is between security and convenience.  The
      more centralized, the easier to secure.

         o What methods will you use for creating accounts and
           terminating access?

      From a security standpoint, you need to examine the mechanism that

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      you will be using to create accounts.  In the least restrictive
      case, the people who are authorized to grant access would be able
      to go into the system directly and create an account by hand or
      through vendor supplied mechanisms.  Generally, these mechanisms
      place a great deal of trust in the person running them, and the
      person running them usually has a large amount of privileges.  If
      this is the choice you make, you need to select someone who is
      trustworthy to perform this task.  The opposite solution is to
      have an integrated system that the people authorized to create
      accounts run, or the users themselves may actually run.  Be aware
      that even in the restrictive case of having a mechanized facility
      to create accounts does not remove the potential for abuse.

      You should have specific procedures developed for the creation of
      accounts.  These procedures should be well documented to prevent
      confusion and reduce mistakes.  A security vulnerability in the
      account authorization process is not only possible through abuse,
      but is also possible if a mistake is made.  Having clear and well
      documented procedure will help ensure that these mistakes won't
      happen.  You should also be sure that the people who will be
      following these procedures understand them.

      The granting of access to users is one of the most vulnerable of
      times.  You should ensure that the selection of an initial
      password cannot be easily guessed.  You should avoid using an
      initial password that is a function of the username, is part of
      the user's name, or some algorithmically generated password that
      can easily be guessed.  In addition, you should not permit users
      to continue to use the initial password indefinitely.  If
      possible, you should force users to change the initial password
      the first time they login.  Consider that some users may never
      even login, leaving their password vulnerable indefinitely.  Some
      sites choose to disable accounts that have never been accessed,
      and force the owner to reauthorize opening the account.

   2.3.4  Who May Have System Administration Privileges?

      One security decision that needs to be made very carefully is who
      will have access to system administrator privileges and passwords
      for your services.  Obviously, the system administrators will need
      access, but inevitably other users will request special
      privileges.  The policy should address this issue.  Restricting
      privileges is one way to deal with threats from local users.  The
      challenge is to balance restricting access to these to protect
      security with giving people who need these privileges access so
      that they can perform their tasks.  One approach that can be taken
      is to grant only enough privilege to accomplish the necessary

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      Additionally, people holding special privileges should be
      accountable to some authority and this should also be identified
      within the site's security policy.  If the people you grant
      privileges to are not accountable, you run the risk of losing
      control of your system and will have difficulty managing a
      compromise in security.

   2.3.5  What Are The Users' Rights and Responsibilities?

      The policy should incorporate a statement on the users' rights and
      responsibilities concerning the use of the site's computer systems
      and services.  It should be clearly stated that users are
      responsible for understanding and respecting the security rules of
      the systems they are using.  The following is a list of topics
      that you may wish to cover in this area of the policy:

         o What guidelines you have regarding resource consumption
           (whether users are restricted, and if so, what the
           restrictions are).
         o What might constitute abuse in terms of system performance.
         o Whether users are permitted to share accounts or let others
           use their accounts.
         o How "secret" users should keep their passwords.
         o How often users should change their passwords and any other
           password restrictions or requirements.
         o Whether you provide backups or expect the users to create
           their own.
         o Disclosure of information that may be proprietary.
         o Statement on Electronic Mail Privacy (Electronic
           Communications Privacy Act).
         o Your policy concerning controversial mail or postings to
           mailing lists or discussion groups (obscenity, harassment,
         o Policy on electronic communications: mail forging, etc.

      The Electronic Mail Association sponsored a white paper on the
      privacy of electronic mail in companies [4].  Their basic
      recommendation is that every site should have a policy on the
      protection of employee privacy.  They also recommend that
      organizations establish privacy policies that deal with all media,
      rather than singling out electronic mail.

      They suggest five criteria for evaluating any policy:

         1. Does the policy comply with law and with duties to
            third parties?

         2. Does the policy unnecessarily compromise the interest of

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            the employee, the employer or third parties?

         3. Is the policy workable as a practical matter and likely to
            be enforced?

         4. Does the policy deal appropriately with all different
            forms of communications and record keeping with the office?

         5. Has the policy been announced in advance and agreed to by
            all concerned?

   2.3.6  What Are The Rights and Responsibilities of System
          Administrators Versus Rights of Users

      There is a tradeoff between a user's right to absolute privacy and
      the need of system administrators to gather sufficient information
      to diagnose problems.  There is also a distinction between a
      system administrator's need to gather information to diagnose
      problems and investigating security violations.  The policy should
      specify to what degree system administrators can examine user
      files to diagnose problems or for other purposes, and what rights
      you grant to the users.  You may also wish to make a statement
      concerning system administrators' obligation to maintaining the
      privacy of information viewed under these circumstances.  A few
      questions that should be answered are:

         o Can an administrator monitor or read a user's files
           for any reason?
         o What are the liabilities?
         o Do network administrators have the right to examine
           network or host traffic?

   2.3.7  What To Do With Sensitive Information

      Before granting users access to your services, you need to
      determine at what level you will provide for the security of data
      on your systems.  By determining this, you are determining the
      level of sensitivity of data that users should store on your
      systems.  You do not want users to store very sensitive
      information on a system that you are not going to secure very
      well.  You need to tell users who might store sensitive
      information what services, if any, are appropriate for the storage
      of sensitive information.  This part should include storing of
      data in different ways (disk, magnetic tape, file servers, etc.).
      Your policy in this area needs to be coordinated with the policy
      concerning the rights of system administrators versus users (see
      section 2.3.6).

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2.4  What Happens When the Policy is Violated

   It is obvious that when any type of official policy is defined, be it
   related to computer security or not, it will eventually be broken.
   The violation may occur due to an individual's negligence, accidental
   mistake, having not been properly informed of the current policy, or
   not understanding the current policy.  It is equally possible that an
   individual (or group of individuals) may knowingly perform an act
   that is in direct violation of the defined policy.

   When a policy violation has been detected, the immediate course of
   action should be pre-defined to ensure prompt and proper enforcement.
   An investigation should be performed to determine how and why the
   violation occurred.  Then the appropriate corrective action should be
   executed.  The type and severity of action taken varies depending on
   the type of violation that occurred.

   2.4.1  Determining the Response to Policy Violations

      Violations to policy may be committed by a wide variety of users.
      Some may be local users and others may be from outside the local
      environment.  Sites may find it helpful to define what it
      considers "insiders" and "outsiders" based upon administrative,
      legal or political boundaries.  These boundaries imply what type
      of action must be taken to correct the offending party; from a
      written reprimand to pressing legal charges.  So, not only do you
      need to define actions based on the type of violation, you also
      need to have a clearly defined series of actions based on the kind
      of user violating your computer security policy.  This all seems
      rather complicated, but should be addressed long before it becomes
      necessary as the result of a violation.

      One point to remember about your policy is that proper education
      is your best defense.  For the outsiders who are using your
      computer legally, it is your responsibility to verify that these
      individuals are aware of the policies that you have set forth.
      Having this proof may assist you in the future if legal action
      becomes necessary.

      As for users who are using your computer illegally, the problem is
      basically the same.  What type of user violated the policy and how
      and why did they do it?  Depending on the results of your
      investigation, you may just prefer to "plug" the hole in your
      computer security and chalk it up to experience.  Or if a
      significant amount of loss was incurred, you may wish to take more
      drastic action.

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   2.4.2  What to do When Local Users Violate the Policy of a Remote

      In the event that a local user violates the security policy of a
      remote site, the local site should have a clearly defined set of
      administrative actions to take concerning that local user.  The
      site should also be prepared to protect itself against possible
      actions by the remote site.  These situations involve legal issues
      which should be addressed when forming the security policy.

   2.4.3  Defining Contacts and Responsibilities to Outside

      The local security policy should include procedures for
      interaction with outside organizations.  These include law
      enforcement agencies, other sites, external response team
      organizations (e.g., the CERT, CIAC) and various press agencies.
      The procedure should state who is authorized to make such contact
      and how it should be handled.  Some questions to be answered

         o Who may talk to the press?
         o When do you contact law enforcement and investigative agencies?
         o If a connection is made from a remote site, is the
           system manager authorized to contact that site?
         o Can data be released?  What kind?

      Detailed contact information should be readily available along
      with clearly defined procedures to follow.

   2.4.4  What are the Responsibilities to our Neighbors and Other
          Internet Sites?

      The Security Policy Working Group within the IETF is working on a
      document entitled, "Policy Guidelines for the Secure Operation of
      the Internet" [23].  It addresses the issue that the Internet is a
      cooperative venture and that sites are expected to provide mutual
      security assistance.  This should be addressed when developing a
      site's policy.  The major issue to be determined is how much
      information should be released.  This will vary from site to site
      according to the type of site (e.g., military, education,
      commercial) as well as the type of security violation that

   2.4.5  Issues for Incident Handling Procedures

      Along with statements of policy, the document being prepared
      should include procedures for incident handling.  This is covered

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      in detail in the next chapter.  There should be procedures
      available that cover all facets of policy violation.

2.5  Locking In or Out

   Whenever a site suffers an incident which may compromise computer
   security, the strategies for reacting may be influenced by two
   opposing pressures.

   If management fears that the site is sufficiently vulnerable, it may
   choose a "Protect and Proceed" strategy.  This approach will have as
   its primary goal the protection and preservation of the site
   facilities and to provide for normalcy for its users as quickly as
   possible.  Attempts will be made to actively interfere with the
   intruder's processes, prevent further access and begin immediate
   damage assessment and recovery.  This process may involve shutting
   down the facilities, closing off access to the network, or other
   drastic measures.  The drawback is that unless the intruder is
   identified directly, they may come back into the site via a different
   path, or may attack another site.

   The alternate approach, "Pursue and Prosecute", adopts the opposite
   philosophy and goals.  The primary goal is to allow intruders to
   continue their activities at the site until the site can identify the
   responsible persons.  This approach is endorsed by law enforcement
   agencies and prosecutors.  The drawback is that the agencies cannot
   exempt a site from possible user lawsuits if damage is done to their
   systems and data.

   Prosecution is not the only outcome possible if the intruder is
   identified.  If the culprit is an employee or a student, the
   organization may choose to take disciplinary actions.  The computer
   security policy needs to spell out the choices and how they will be
   selected if an intruder is caught.

   Careful consideration must be made by site management regarding their
   approach to this issue before the problem occurs.  The strategy
   adopted might depend upon each circumstance.  Or there may be a
   global policy which mandates one approach in all circumstances.  The
   pros and cons must be examined thoroughly and the users of the
   facilities must be made aware of the policy so that they understand
   their vulnerabilities no matter which approach is taken.

   The following are checklists to help a site determine which strategy
   to adopt: "Protect and Proceed" or "Pursue and Prosecute".

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   Protect and Proceed

      1. If assets are not well protected.

      2. If continued penetration could result in great
         financial risk.

      3. If the possibility or willingness to prosecute
         is not present.

      4. If user base is unknown.

      5. If users are unsophisticated and their work is

      6. If the site is vulnerable to lawsuits from users, e.g.,
         if their resources are undermined.

   Pursue and Prosecute

      1. If assets and systems are well protected.

      2. If good backups are available.

      3. If the risk to the assets is outweighed by the
         disruption caused by the present and possibly future

      4. If this is a concentrated attack occurring with great
         frequency and intensity.

      5. If the site has a natural attraction to intruders, and
         consequently regularly attracts intruders.

      6. If the site is willing to incur the financial (or other)
         risk to assets by allowing the penetrator continue.

      7. If intruder access can be controlled.

      8. If the monitoring tools are sufficiently well-developed
         to make the pursuit worthwhile.

      9. If the support staff is sufficiently clever and knowledgable
         about the operating system, related utilities, and systems
         to make the pursuit worthwhile.

      10. If there is willingness on the part of management to

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      11. If the system adminitrators know in general what kind of
          evidence would lead to prosecution.

      12. If there is established contact with knowledgeable law

      13. If there is a site representative versed in the relevant
          legal issues.

      14. If the site is prepared for possible legal action from
          its own users if their data or systems become compromised
          during the pursuit.

2.6  Interpreting the Policy

   It is important to define who will interpret the policy.  This could
   be an individual or a committee.  No matter how well written, the
   policy will require interpretation from time to time and this body
   would serve to review, interpret, and revise the policy as needed.

2.7  Publicizing the Policy

   Once the site security policy has been written and established, a
   vigorous process should be engaged to ensure that the policy
   statement is widely and thoroughly disseminated and discussed.  A
   mailing of the policy should not be considered sufficient.  A period
   for comments should be allowed before the policy becomes effective to
   ensure that all affected users have a chance to state their reactions
   and discuss any unforeseen ramifications.  Ideally, the policy should
   strike a balance between protection and productivity.

   Meetings should be held to elicit these comments, and also to ensure
   that the policy is correctly understood.  (Policy promulgators are
   not necessarily noted for their skill with the language.)  These
   meetings should involve higher management as well as line employees.
   Security is a collective effort.

   In addition to the initial efforts to publicize the policy, it is
   essential for the site to maintain a continual awareness of its
   computer security policy.  Current users may need periodic reminders
   New users should have the policy included as part of their site
   introduction packet.  As a condition for using the site facilities,
   it may be advisable to have them sign a statement that they have read
   and understood the policy.  Should any of these users require legal
   action for serious policy violations, this signed statement might
   prove to be a valuable aid.

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3.  Establishing Procedures to Prevent Security Problems

   The security policy defines what needs to be protected.  This section
   discusses security procedures which specify what steps will be used
   to carry out the security policy.

3.1  Security Policy Defines What Needs to be Protected

   The security policy defines the WHAT's: what needs to be protected,
   what is most important, what the priorities are, and what the general
   approach to dealing with security problems should be.

   The security policy by itself doesn't say HOW things are protected.
   That is the role of security procedures, which this section
   discusses.  The security policy should be a high level document,
   giving general strategy.  The security procedures need to set out, in
   detail, the precise steps your site will take to protect itself.

   The security policy should include a general risk assessment of the
   types of threats a site is mostly likely to face and the consequences
   of those threats (see section 2.2).  Part of doing a risk assessment
   will include creating a general list of assets that should be
   protected (section 2.2.2).  This information is critical in devising
   cost-effective procedures.

   It is often tempting to start creating security procedures by
   deciding on different mechanisms first: "our site should have logging
   on all hosts, call-back modems, and smart cards for all users."  This
   approach could lead to some areas that have too much protection for
   the risk they face, and other areas that aren't protected enough.
   Starting with the security policy and the risks it outlines should
   ensure that the procedures provide the right level of protect for all

3.2  Identifing Possible Problems

   To determine risk, vulnerabilities must be identified.  Part of the
   purpose of the policy is to aid in shoring up the vulnerabilities and
   thus to decrease the risk in as many areas as possible.  Several of
   the more popular problem areas are presented in sections below.  This
   list is by no means complete.  In addition, each site is likely to
   have a few unique vulnerabilities.

   3.2.1  Access Points

      Access points are typically used for entry by unauthorized users.
      Having many access points increases the risk of access to an
      organization's computer and network facilities.

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      Network links to networks outside the organization allow access
      into the organization for all others connected to that external
      network.  A network link typically provides access to a large
      number of network services, and each service has a potential to be

      Dialup lines, depending on their configuration, may provide access
      merely to a login port of a single system.  If connected to a
      terminal server, the dialup line may give access to the entire

      Terminal servers themselves can be a source of problem.  Many
      terminal servers do not require any kind of authentication.
      Intruders often use terminal servers to disguise their actions,
      dialing in on a local phone and then using the terminal server to
      go out to the local network.  Some terminal servers are configured
      so that intruders can TELNET [19] in from outside the network, and
      then TELNET back out again, again serving to make it difficult to
      trace them.

   3.2.2  Misconfigured Systems

      Misconfigured systems form a large percentage of security holes.
      Today's operating systems and their associated software have
      become so complex that understanding how the system works has
      become a full-time job.  Often, systems managers will be non-
      specialists chosen from the current organization's staff.

      Vendors are also partly responsible for misconfigured systems. To
      make the system installation process easier, vendors occasionally
      choose initial configurations that are not secure in all

   3.2.3  Software Bugs

      Software will never be bug free.  Publicly known security bugs are
      common methods of unauthorized entry.  Part of the solution to
      this problem is to be aware of the security problems and to update
      the software when problems are detected.  When bugs are found,
      they should be reported to the vendor so that a solution to the
      problem can be implemented and distributed.

   3.2.4  "Insider" Threats

      An insider to the organization may be a considerable threat to the
      security of the computer systems.  Insiders often have direct
      access to the computer and network hardware components.  The
      ability to access the components of a system makes most systems

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      easier to compromise.  Most desktop workstations can be easily
      manipulated so that they grant privileged access.  Access to a
      local area network provides the ability to view possibly sensitive
      data traversing the network.

3.3  Choose Controls to Protect Assets in a Cost-Effective Way

   After establishing what is to be protected, and assessing the risks
   these assets face, it is necessary to decide how to implement the
   controls which protect these assets.  The controls and protection
   mechanisms should be selected in a way so as to adequately counter
   the threats found during risk assessment, and to implement those
   controls in a cost effective manner.  It makes little sense to spend
   an exorbitant sum of money and overly constrict the user base if the
   risk of exposure is very small.

   3.3.1  Choose the Right Set of Controls

      The controls that are selected represent the physical embodiment
      of your security policy.  They are the first and primary line of
      defense in the protection of your assets.  It is therefore most
      important to ensure that the controls that you select are the
      right set of controls.  If the major threat to your system is
      outside penetrators, it probably doesn't make much sense to use
      biometric devices to authenticate your regular system users.  On
      the other hand, if the major threat is unauthorized use of
      computing resources by regular system users, you'll probably want
      to establish very rigorous automated accounting procedures.

   3.3.2  Use Common Sense

      Common sense is the most appropriate tool that can be used to
      establish your security policy.  Elaborate security schemes and
      mechanisms are impressive, and they do have their place, yet there
      is little point in investing money and time on an elaborate
      implementation scheme if the simple controls are forgotten.  For
      example, no matter how elaborate a system you put into place on
      top of existing security controls, a single user with a poor
      password can still leave your system open to attack.

3.4  Use Multiple Strategies to Protect Assets

   Another method of protecting assets is to use multiple strategies.
   In this way, if one strategy fails or is circumvented, another
   strategy comes into play to continue protecting the asset.  By using
   several simpler strategies, a system can often be made more secure
   than if one very sophisticated method were used in its place.  For
   example, dial-back modems can be used in conjunction with traditional

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   logon mechanisms.  Many similar approaches could be devised that
   provide several levels of protection for assets.  However, it's very
   easy to go overboard with extra mechanisms.  One must keep in mind
   exactly what it is that needs to be protected.

3.5  Physical Security

   It is a given in computer security if the system itself is not
   physically secure, nothing else about the system can be considered
   secure.  With physical access to a machine, an intruder can halt the
   machine, bring it back up in privileged mode, replace or alter the
   disk, plant Trojan horse programs (see section, or take any
   number of other undesirable (and hard to prevent) actions.

   Critical communications links, important servers, and other key
   machines should be located in physically secure areas.  Some security
   systems (such as Kerberos) require that the machine be physically

   If you cannot physically secure machines, care should be taken about
   trusting those machines.  Sites should consider limiting access from
   non-secure machines to more secure machines.  In particular, allowing
   trusted access (e.g., the BSD Unix remote commands such as rsh) from
   these kinds of hosts is particularly risky.

   For machines that seem or are intended to be physically secure, care
   should be taken about who has access to the machines.  Remember that
   custodial and maintenance staff often have keys to rooms.

3.6   Procedures to Recognize Unauthorized Activity

   Several simple procedures can be used to detect most unauthorized
   uses of a computer system.  These procedures use tools provided with
   the operating system by the vendor, or tools publicly available from
   other sources.

   3.6.1  Monitoring System Use

      System monitoring can be done either by a system administrator, or
      by software written for the purpose.  Monitoring a system involves
      looking at several parts of the system and searching for anything
      unusual.  Some of the easier ways to do this are described in this

      The most important thing about monitoring system use is that it be
      done on a regular basis.  Picking one day out of the month to
      monitor the system is pointless, since a security breach can be
      isolated to a matter of hours.  Only by maintaining a constant

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      vigil can you expect to detect security violations in time to
      react to them.

   3.6.2  Tools for Monitoring the System

      This section describes tools and methods for monitoring a system
      against unauthorized access and use.  Logging

         Most operating systems store numerous bits of information in
         log files.  Examination of these log files on a regular basis
         is often the first line of defense in detecting unauthorized
         use of the system.

            - Compare lists of currently logged in users and past
              login histories.  Most users typically log in and out
              at roughly the same time each day.  An account logged
              in outside the "normal" time for the account may be in
              use by an intruder.

            - Many systems maintain accounting records for billing
              purposes.  These records can also be used to determine
              usage patterns for the system; unusual accounting records
              may indicate unauthorized use of the system.

            - System logging facilities, such as the UNIX "syslog"
              utility, should be checked for unusual error messages
              from system software.  For example, a large number of
              failed login attempts in a short period of time may
              indicate someone trying to guess passwords.

            - Operating system commands which list currently executing
              processes can be used to detect users running programs
              they are not authorized to use, as well as to detect
              unauthorized programs which have been started by an
              intruder.  Monitoring Software

         Other monitoring tools can easily be constructed using standard
         operating system software, by using several, often unrelated,
         programs together.  For example, checklists of file ownerships
         and permission settings can be constructed (for example, with
         "ls" and "find" on UNIX) and stored off-line.  These lists can
         then be reconstructed periodically and compared against the
         master checklist (on UNIX, by using the "diff" utility).
         Differences may indicate that unauthorized modifications have

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         been made to the system.

         Still other tools are available from third-party vendors and
         public software distribution sites.  Section 3.9.9 lists
         several sources from which you can learn what tools are
         available and how to get them.  Other Tools

         Other tools can also be used to monitor systems for security
         violations, although this is not their primary purpose.  For
         example, network monitors can be used to detect and log
         connections from unknown sites.

   3.6.3  Vary the Monitoring Schedule

      The task of system monitoring is not as daunting as it may seem.
      System administrators can execute many of the commands used for
      monitoring periodically throughout the day during idle moments
      (e.g., while talking on the telephone), rather than spending fixed
      periods of each day monitoring the system.  By executing the
      commands frequently, you will rapidly become used to seeing
      "normal" output, and will easily spot things which are out of the
      ordinary.  In addition, by running various monitoring commands at
      different times throughout the day, you make it hard for an
      intruder to predict your actions.  For example, if an intruder
      knows that each day at 5:00 p.m. the system is checked to see that
      everyone has logged off, he will simply wait until after the check
      has completed before logging in.  But the intruder cannot guess
      when a system administrator might type a command to display all
      logged-in users, and thus he runs a much greater risk of

      Despite the advantages that regular system monitoring provides,
      some intruders will be aware of the standard logging mechanisms in
      use on systems they are attacking.  They will actively pursue and
      attempt to disable monitoring mechanisms.  Regular monitoring
      therefore is useful in detecting intruders, but does not provide
      any guarantee that your system is secure, nor should monitoring be
      considered an infallible method of detecting unauthorized use.

3.7  Define Actions to Take When Unauthorized Activity is Suspected

      Sections 2.4 and 2.5 discussed the course of action a site should
      take when it suspects its systems are being abused.  The computer
      security policy should state the general approach towards dealing
      with these problems.

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      The procedures for dealing with these types of problems should be
      written down.  Who has authority to decide what actions will be
      taken?  Should law enforcement be involved?  Should your
      organization cooperate with other sites in trying to track down an
      intruder?  Answers to all the questions in section 2.4 should be
      part of the incident handling procedures.

      Whether you decide to lock out or pursue intruders, you should
      have tools and procedures ready to apply.  It is best to work up
      these tools and procedures before you need them.  Don't wait until
      an intruder is on your system to figure out how to track the
      intruder's actions; you will be busy enough if an intruder

3.8  Communicating Security Policy

   Security policies, in order to be effective, must be communicated to
   both the users of the system and the system maintainers.  This
   section describes what these people should be told, and how to tell

   3.8.1  Educating the Users

      Users should be made aware of how the computer systems are
      expected to be used, and how to protect themselves from
      unauthorized users.  Proper Account/Workstation Use

         All users should be informed about what is considered the
         "proper" use of their account or workstation ("proper" use is
         discussed in section 2.3.2).  This can most easily be done at
         the time a user receives their account, by giving them a policy
         statement.  Proper use policies typically dictate things such
         as whether or not the account or workstation may be used for
         personal activities (such as checkbook balancing or letter
         writing), whether profit-making activities are allowed, whether
         game playing is permitted, and so on.  These policy statements
         may also be used to summarize how the computer facility is
         licensed and what software licenses are held by the
         institution; for example, many universities have educational
         licenses which explicitly prohibit commercial uses of the
         system.  A more complete list of items to consider when writing
         a policy statement is given in section 2.3.  Account/Workstation Management Procedures

         Each user should be told how to properly manage their account

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         and workstation.  This includes explaining how to protect files
         stored on the system, how to log out or lock the terminal or
         workstation, and so on.  Much of this information is typically
         covered in the "beginning user" documentation provided by the
         operating system vendor, although many sites elect to
         supplement this material with local information.

         If your site offers dial-up modem access to the computer
         systems, special care must be taken to inform users of the
         security problems inherent in providing this access.  Issues
         such as making sure to log out before hanging up the modem
         should be covered when the user is initially given dial-up

         Likewise, access to the systems via local and wide-area
         networks presents its own set of security problems which users
         should be made aware of.  Files which grant "trusted host" or
         "trusted user" status to remote systems and users should be
         carefully explained.  Determining Account Misuse

         Users should be told how to detect unauthorized access to their
         account.  If the system prints the last login time when a user
         logs in, he or she should be told to check that time and note
         whether or not it agrees with the last time he or she actually
         logged in.

         Command interpreters on some systems (e.g., the UNIX C shell)
         maintain histories of the last several commands executed.
         Users should check these histories to be sure someone has not
         executed other commands with their account.  Problem Reporting Procedures

         A procedure should be developed to enable users to report
         suspected misuse of their accounts or other misuse they may
         have noticed.  This can be done either by providing the name
         and telephone number of a system administrator who manages
         security of the computer system, or by creating an electronic
         mail address (e.g., "security") to which users can address
         their problems.

   3.8.2  Educating the Host Administrators

      In many organizations, computer systems are administered by a wide
      variety of people.  These administrators must know how to protect
      their own systems from attack and unauthorized use, as well as how

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      to communicate successful penetration of their systems to other
      administrators as a warning.  Account Management Procedures

         Care must be taken when installing accounts on the system in
         order to make them secure.  When installing a system from
         distribution media, the password file should be examined for
         "standard" accounts provided by the vendor.  Many vendors
         provide accounts for use by system services or field service
         personnel.  These accounts typically have either no password or
         one which is common knowledge.  These accounts should be given
         new passwords if they are needed, or disabled or deleted from
         the system if they are not.

         Accounts without passwords are generally very dangerous since
         they allow anyone to access the system.  Even accounts which do
         not execute a command interpreter (e.g., accounts which exist
         only to see who is logged in to the system) can be compromised
         if set up incorrectly.  A related concept, that of "anonymous"
         file transfer (FTP) [20], allows users from all over the
         network to access your system to retrieve files from (usually)
         a protected disk area.  You should carefully weigh the benefits
         that an account without a password provides against the
         security risks of providing such access to your system.

         If the operating system provides a "shadow" password facility
         which stores passwords in a separate file accessible only to
         privileged users, this facility should be used.  System V UNIX,
         SunOS 4.0 and above, and versions of Berkeley UNIX after 4.3BSD
         Tahoe, as well as others, provide this feature.  It protects
         passwords by hiding their encrypted values from unprivileged
         users.  This prevents an attacker from copying your password
         file to his or her machine and then attempting to break the
         passwords at his or her leisure.

         Keep track of who has access to privileged user accounts (e.g.,
         "root" on UNIX or "MAINT" on VMS).  Whenever a privileged user
         leaves the organization or no longer has need of the privileged
         account, the passwords on all privileged accounts should be
         changed.  Configuration Management Procedures

         When installing a system from the distribution media or when
         installing third-party software, it is important to check the
         installation carefully.  Many installation procedures assume a
         "trusted" site, and hence will install files with world write

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         permission enabled, or otherwise compromise the security of

         Network services should also be examined carefully when first
         installed.  Many vendors provide default network permission
         files which imply that all outside hosts are to be "trusted",
         which is rarely the case when connected to wide-area networks
         such as the Internet.

         Many intruders collect information on the vulnerabilities of
         particular system versions.  The older a system, the more
         likely it is that there are security problems in that version
         which have since been fixed by the vendor in a later release.
         For this reason, it is important to weigh the risks of not
         upgrading to a new operating system release (thus leaving
         security holes unplugged) against the cost of upgrading to the
         new software (possibly breaking third-party software, etc.).
         Bug fixes from the vendor should be weighed in a similar
         fashion, with the added note that "security" fixes from a
         vendor usually address fairly serious security problems.

         Other bug fixes, received via network mailing lists and the
         like, should usually be installed, but not without careful
         examination.  Never install a bug fix unless you're sure you
         know what the consequences of the fix are - there's always the
         possibility that an intruder has suggested a "fix" which
         actually gives him or her access to your system.  Recovery Procedures - Backups

         It is impossible to overemphasize the need for a good backup
         strategy.  File system backups not only protect you in the
         event of hardware failure or accidental deletions, but they
         also protect you against unauthorized changes made by an
         intruder.  Without a copy of your data the way it's "supposed"
         to be, it can be difficult to undo something an attacker has

         Backups, especially if run daily, can also be useful in
         providing a history of an intruder's activities.  Looking
         through old backups can establish when your system was first
         penetrated.  Intruders may leave files around which, although
         deleted later, are captured on the backup tapes.  Backups can
         also be used to document an intruder's activities to law
         enforcement agencies if necessary.

         A good backup strategy will dump the entire system to tape at
         least once a month.  Partial (or "incremental") dumps should be

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         done at least twice a week, and ideally they should be done
         daily.  Commands specifically designed for performing file
         system backups (e.g., UNIX "dump" or VMS "BACKUP") should be
         used in preference to other file copying commands, since these
         tools are designed with the express intent of restoring a
         system to a known state.  Problem Reporting Procedures

         As with users, system administrators should have a defined
         procedure for reporting security problems.  In large
         installations, this is often done by creating an electronic
         mail alias which contains the names of all system
         administrators in the organization.  Other methods include
         setting up some sort of response team similar to the CERT, or
         establishing a "hotline" serviced by an existing support group.

3.9  Resources to Prevent Security Breaches

   This section discusses software, hardware, and procedural resources
   that can be used to support your site security policy.

   3.9.1  Network Connections and Firewalls

      A "firewall" is put in place in a building to provide a point of
      resistance to the entry of flames into another area.  Similarly, a
      secretary's desk and reception area provides a point of
      controlling access to other office spaces.  This same technique
      can be applied to a computer site, particularly as it pertains to
      network connections.

      Some sites will be connected only to other sites within the same
      organization and will not have the ability to connect to other
      networks.  Sites such as these are less susceptible to threats
      from outside their own organization, although intrusions may still
      occur via paths such as dial-up modems.  On the other hand, many
      other organizations will be connected to other sites via much
      larger networks, such as the Internet.  These sites are
      susceptible to the entire range of threats associated with a
      networked environment.

      The risks of connecting to outside networks must be weighed
      against the benefits.  It may be desirable to limit connection to
      outside networks to those hosts which do not store sensitive
      material, keeping "vital" machines (such as those which maintain
      company payroll or inventory systems) isolated.  If there is a
      need to participate in a Wide Area Network (WAN), consider
      restricting all access to your local network through a single

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      system.  That is, all access to or from your own local network
      must be made through a single host computer that acts as a
      firewall between you and the outside world.  This firewall system
      should be rigorously controlled and password protected, and
      external users accessing it should also be constrained by
      restricting the functionality available to remote users.  By using
      this approach, your site could relax some of the internal security
      controls on your local net, but still be afforded the protection
      of a rigorously controlled host front end.

      Note that even with a firewall system, compromise of the firewall
      could result in compromise of the network behind the firewall.
      Work has been done in some areas to construct a firewall which
      even when compromised, still protects the local network [6,

   3.9.2  Confidentiality

      Confidentiality, the act of keeping things hidden or secret, is
      one of the primary goals of computer security practitioners.
      Several mechanisms are provided by most modern operating systems
      to enable users to control the dissemination of information.
      Depending upon where you work, you may have a site where
      everything is protected, or a site where all information is
      usually regarded as public, or something in-between.  Most sites
      lean toward the in-between, at least until some penetration has

      Generally, there are three instances in which information is
      vulnerable to disclosure: when the information is stored on a
      computer system, when the information is in transit to another
      system (on the network), and when the information is stored on
      backup tapes.

      The first of these cases is controlled by file permissions, access
      control lists, and other similar mechanisms.  The last can be
      controlled by restricting access to the backup tapes (by locking
      them in a safe, for example).  All three cases can be helped by
      using encryption mechanisms.  Encryption (hardware and software)

         Encryption is the process of taking information that exists in
         some readable form and converting it into a non-readable form.
         There are several types of commercially available encryption
         packages in both hardware and software forms.  Hardware
         encryption engines have the advantage that they are much faster
         than the software equivalent, yet because they are faster, they

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         are of greater potential benefit to an attacker who wants to
         execute a brute-force attack on your encrypted information.

         The advantage of using encryption is that, even if other access
         control mechanisms (passwords, file permissions, etc.) are
         compromised by an intruder, the data is still unusable.
         Naturally, encryption keys and the like should be protected at
         least as well as account passwords.

         Information in transit (over a network) may be vulnerable to
         interception as well.  Several solutions to this exist, ranging
         from simply encrypting files before transferring them (end-to-
         end encryption) to special network hardware which encrypts
         everything it sends without user intervention (secure links).
         The Internet as a whole does not use secure links, thus end-
         to-end encryption must be used if encryption is desired across
         the Internet.
  Data Encryption Standard (DES)

            DES is perhaps the most widely used data encryption
            mechanism today.  Many hardware and software implementations
            exist, and some commercial computers are provided with a
            software version.  DES transforms plain text information
            into encrypted data (or ciphertext) by means of a special
            algorithm and "seed" value called a key.  So long as the key
            is retained (or remembered) by the original user, the
            ciphertext can be restored to the original plain text.

            One of the pitfalls of all encryption systems is the need to
            remember the key under which a thing was encrypted (this is
            not unlike the password problem discussed elsewhere in this
            document).  If the key is written down, it becomes less
            secure.  If forgotten, there is little (if any) hope of
            recovering the original data.

            Most UNIX systems provide a DES command that enables a user
            to encrypt data using the DES algorithm.

            Similar to the DES command, the UNIX "crypt" command allows
            a user to encrypt data.  Unfortunately, the algorithm used
            by "crypt" is very insecure (based on the World War II
            "Enigma" device), and files encrypted with this command can
            be decrypted easily in a matter of a few hours.  Generally,
            use of the "crypt" command should be avoided for any but the
            most trivial encryption tasks.

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RFC 1244                 Site Security Handbook                July 1991  Privacy Enhanced Mail

         Electronic mail normally transits the network in the clear
         (i.e., anyone can read it).  This is obviously not the optimal
         solution.  Privacy enhanced mail provides a means to
         automatically encrypt electronic mail messages so that a person
         eavesdropping at a mail distribution node is not (easily)
         capable of reading them.  Several privacy enhanced mail
         packages are currently being developed and deployed on the

         The Internet Activities Board Privacy Task Force has defined a
         draft standard, elective protocol for use in implementing
         privacy enhanced mail.  This protocol is defined in RFCs 1113,
         1114, and 1115 [7,8,9].  Please refer to the current edition of
         the "IAB Official Protocol Standards" (currently, RFC 1200
         [21]) for the standardization state and status of these

   3.9.3  Origin Authentication

      We mostly take it on faith that the header of an electronic mail
      message truly indicates the originator of a message.  However, it
      iseasy to "spoof", or forge the source of a mail message.  Origin
      authentication provides a means to be certain of the originator of
      a message or other object in the same way that a Notary Public
      assures a signature on a legal document.  This is done by means of
      a "Public Key" cryptosystem.

      A public key cryptosystem differs from a private key cryptosystem
      in several ways.  First, a public key system uses two keys, a
      Public Key that anyone can use (hence the name) and a Private Key
      that only the originator of a message uses.  The originator uses
      the private key to encrypt the message (as in DES).  The receiver,
      who has obtained the public key for the originator, may then
      decrypt the message.

      In this scheme, the public key is used to authenticate the
      originator's use of his or her private key, and hence the identity
      of the originator is more rigorously proven.  The most widely
      known implementation of a public key cryptosystem is the RSA
      system [26].  The Internet standard for privacy enhanced mail
      makes use of the RSA system.

   3.9.4  Information Integrity

      Information integrity refers to the state of information such that
      it is complete, correct, and unchanged from the last time in which

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      it was verified to be in an "integral" state.  The value of
      information integrity to a site will vary.  For example, it is
      more important for military and government installations to
      prevent the "disclosure" of classified information, whether it is
      right or wrong.  A bank, on the other hand, is far more concerned
      with whether the account information maintained for its customers
      is complete and accurate.

      Numerous computer system mechanisms, as well as procedural
      controls, have an influence on the integrity of system
      information.  Traditional access control mechanisms maintain
      controls over who can access system information.  These mechanisms
      alone are not sufficient in some cases to provide the degree of
      integrity required.  Some other mechanisms are briefly discussed

      It should be noted that there are other aspects to maintaining
      system integrity besides these mechanisms, such as two-person
      controls, and integrity validation procedures.  These are beyond
      the scope of this document.  Checksums

         Easily the simplest mechanism, a simple checksum routine can
         compute a value for a system file and compare it with the last
         known value.  If the two are equal, the file is probably
         unchanged.  If not, the file has been changed by some unknown

         Though it is the easiest to implement, the checksum scheme
         suffers from a serious failing in that it is not very
         sophisticated and a determined attacker could easily add enough
         characters to the file to eventually obtain the correct value.

         A specific type of checksum, called a CRC checksum, is
         considerably more robust than a simple checksum.  It is only
         slightly more difficult to implement and provides a better
         degree of catching errors.  It too, however, suffers from the
         possibility of compromise by an attacker.

         Checksums may be used to detect the altering of information.
         However, they do not actively guard against changes being made.
         For this, other mechanisms such as access controls and
         encryption should be used.

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RFC 1244                 Site Security Handbook                July 1991  Cryptographic Checksums

         Cryptographic checksums (also called cryptosealing) involve
         breaking a file up into smaller chunks, calculating a (CRC)
         checksum for each chunk, and adding the CRCs together.
         Depending upon the exact algorithm used, this can result in a
         nearly unbreakable method of determining whether a file has
         been changed.  This mechanism suffers from the fact that it is
         sometimes computationally intensive and may be prohibitive
         except in cases where the utmost integrity protection is

         Another related mechanism, called a one-way hash function (or a
         Manipulation Detection Code (MDC)) can also be used to uniquely
         identify a file.  The idea behind these functions is that no
         two inputs can produce the same output, thus a modified file
         will not have the same hash value.  One-way hash functions can
         be implemented efficiently on a wide variety of systems, making
         unbreakable integrity checks possible.  (Snefru, a one-way hash
         function available via USENET as well as the Internet is just
         one example of an efficient one-way hash function.) [10]

   3.9.5  Limiting Network Access

      The dominant network protocols in use on the Internet, IP (RFC
      791) [11], TCP (RFC 793) [12], and UDP (RFC 768) [13], carry
      certain control information which can be used to restrict access
      to certain hosts or networks within an organization.

      The IP packet header contains the network addresses of both the
      sender and recipient of the packet.  Further, the TCP and UDP
      protocols provide the notion of a "port", which identifies the
      endpoint (usually a network server) of a communications path.  In
      some instances, it may be desirable to deny access to a specific
      TCP or UDP port, or even to certain hosts and networks altogether.  Gateway Routing Tables

         One of the simplest approaches to preventing unwanted network
         connections is to simply remove certain networks from a
         gateway's routing tables.  This makes it "impossible" for a
         host to send packets to these networks.  (Most protocols
         require bidirectional packet flow even for unidirectional data
         flow, thus breaking one side of the route is usually

         This approach is commonly taken in "firewall" systems by
         preventing the firewall from advertising local routes to the

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         outside world.  The approach is deficient in that it often
         prevents "too much" (e.g., in order to prevent access to one
         system on the network, access to all systems on the network is
         disabled).  Router Packet Filtering

         Many commercially available gateway systems (more correctly
         called routers) provide the ability to filter packets based not
         only on sources or destinations, but also on source-destination
         combinations.  This mechanism can be used to deny access to a
         specific host, network, or subnet from any other host, network,
         or subnet.

         Gateway systems from some vendors (e.g., cisco Systems) support
         an even more complex scheme, allowing finer control over source
         and destination addresses.  Via the use of address masks, one
         can deny access to all but one host on a particular network.
         The cisco Systems also allow packet screening based on IP
         protocol type and TCP or UDP port numbers [14].

         This can also be circumvented by "source routing" packets
         destined for the "secret" network.  Source routed packets may
         be filtered out by gateways, but this may restrict other
         legitimate activities, such as diagnosing routing problems.

   3.9.6  Authentication Systems

      Authentication refers to the process of proving a claimed identity
      to the satisfaction of some permission-granting authority.
      Authentication systems are hardware, software, or procedural
      mechanisms that enable a user to obtain access to computing
      resources.  At the simplest level, the system administrator who
      adds new user accounts to the system is part of the system
      authentication mechanism.  At the other end of the spectrum,
      fingerprint readers or retinal scanners provide a very high-tech
      solution to establishing a potential user's identity.  Without
      establishing and proving a user's identity prior to establishing a
      session, your site's computers are vulnerable to any sort of

      Typically, a user authenticates himself or herself to the system
      by entering a password in response to a prompt.
      Challenge/Response mechanisms improve upon passwords by prompting
      the user for some piece of information shared by both the computer
      and the user (such as mother's maiden name, etc.).

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RFC 1244                 Site Security Handbook                July 1991  Kerberos

         Kerberos, named after the dog who in mythology is said to stand
         at the gates of Hades, is a collection of software used in a
         large network to establish a user's claimed identity.
         Developed at the Massachusetts Institute of Technology (MIT),
         it uses a combination of encryption and distributed databases
         so that a user at a campus facility can login and start a
         session from any computer located on the campus.  This has
         clear advantages in certain environments where there are a
         large number of potential users who may establish a connection
         from any one of a large number of workstations.  Some vendors
         are now incorporating Kerberos into their systems.

         It should be noted that while Kerberos makes several advances
         in the area of authentication, some security weaknesses in the
         protocol still remain [15].  Smart Cards

         Several systems use "smart cards" (a small calculator-like
         device) to help authenticate users.  These systems depend on
         the user having an object in their possession.  One such system
         involves a new password procedure that require a user to enter
         a value obtained from a "smart card" when asked for a password
         by the computer.  Typically, the host machine will give the
         user some piece of information that is entered into the
         keyboard of the smart card.  The smart card will display a
         response which must then be entered into the computer before
         the session will be established.  Another such system involves
         a smart card which displays a number which changes over time,
         but which is synchronized with the authentication software on
         the computer.

         This is a better way of dealing with authentication than with
         the traditional password approach.  On the other hand, some say
         it's inconvenient to carry the smart card.  Start-up costs are
         likely to be high as well.

   3.9.7  Books, Lists, and Informational Sources

      There are many good sources for information regarding computer
      security.  The annotated bibliography at the end of this document
      can provide you with a good start.  In addition, information can
      be obtained from a variety of other sources, some of which are
      described in this section.

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RFC 1244                 Site Security Handbook                July 1991  Security Mailing Lists

         The UNIX Security mailing list exists to notify system
         administrators of security problems before they become common
         knowledge, and to provide security enhancement information.  It
         is a restricted-access list, open only to people who can be
         verified as being principal systems people at a site.  Requests
         to join the list must be sent by either the site contact listed
         in the Defense Data Network's Network Information Center's (DDN
         NIC) WHOIS database, or from the "root" account on one of the
         major site machines.  You must include the destination address
         you want on the list, an indication of whether you want to be
         on the mail reflector list or receive weekly digests, the
         electronic mail address and voice telephone number of the site
         contact if it isn't you, and the name, address, and telephone
         number of your organization.  This information should be sent

         The RISKS digest is a component of the ACM Committee on
         Computers and Public Policy, moderated by Peter G. Neumann.  It
         is a discussion forum on risks to the public in computers and
         related systems, and along with discussing computer security
         and privacy issues, has discussed such subjects as the Stark
         incident, the shooting down of the Iranian airliner in the
         Persian Gulf (as it relates to the computerized weapons
         systems), problems in air and railroad traffic control systems,
         software engineering, and so on.  To join the mailing list,
         send a message to RISKS-REQUEST@CSL.SRI.COM.  This list is also
         available in the USENET newsgroup "comp.risks".

         The VIRUS-L list is a forum for the discussion of computer
         virus experiences, protection software, and related topics.
         The list is open to the public, and is implemented as a
         moderated digest.  Most of the information is related to
         personal computers, although some of it may be applicable to
         larger systems.  To subscribe, send the line:

            SUB VIRUS-L your full name

         to the address LISTSERV%LEHIIBM1.BITNET@MITVMA.MIT.EDU.  This
         list is also available via the USENET newsgroup "comp.virus".

         The Computer Underground Digest "is an open forum dedicated to
         sharing information among computerists and to the presentation
         and debate of diverse views."  While not directly a security
         list, it does contain discussions about privacy and other
         security related topics.  The list can be read on USENET as, or to join the mailing list, send mail

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         to Gordon Myer (
         Submissions may be mailed to:  Networking Mailing Lists

         The TCP-IP mailing list is intended to act as a discussion
         forum for developers and maintainers of implementations of the
         TCP/IP protocol suite.  It also discusses network-related
         security problems when they involve programs providing network
         services, such as "Sendmail".  To join the TCP-IP list, send a
         message to TCP-IP-REQUEST@NISC.SRI.COM.  This list is also
         available in the USENET newsgroup "comp.protocols.tcp-ip".

         SUN-NETS is a discussion list for items pertaining to
         networking on Sun systems.  Much of the discussion is related
         to NFS, NIS (formally Yellow Pages), and name servers.  To
         subscribe, send a message to SUN-NETS-REQUEST@UMIACS.UMD.EDU.

         The USENET groups and also discuss
         security issues. is a moderated group and also
         includes discussions of physical security and locks. is unmoderated.  Response Teams

         Several organizations have formed special groups of people to
         deal with computer security problems.  These teams collect
         information about possible security holes and disseminate it to
         the proper people, track intruders, and assist in recovery from
         security violations.  The teams typically have both electronic
         mail distribution lists as well as a special telephone number
         which can be called for information or to report a problem.
         Many of these teams are members of the CERT System, which is
         coordinated by the National Institute of Standards and
         Technology (NIST), and exists to facilitate the exchange of
         information between the various teams.
  DARPA Computer Emergency Response Team

            The Computer Emergency Response Team/Coordination Center
            (CERT/CC) was established in December 1988 by the Defense
            Advanced Research Projects Agency (DARPA) to address
            computer security concerns of research users of the
            Internet.  It is operated by the Software Engineering
            Institute (SEI) at Carnegie-Mellon University (CMU).  The
            CERT can immediately confer with experts to diagnose and
            solve security problems, and also establish and maintain
            communications with the affected computer users and

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            government authorities as appropriate.

            The CERT/CC serves as a clearing house for the
            identification and repair of security vulnerabilities,
            informal assessments of existing systems, improvement of
            emergency response capability, and both vendor and user
            security awareness.  In addition, the team works with
            vendors of various systems in order to coordinate the fixes
            for security problems.

            The CERT/CC sends out security advisories to the CERT-
            ADVISORY mailing list whenever appropriate.  They also
            operate a 24-hour hotline that can be called to report
            security problems (e.g., someone breaking into your system),
            as well as to obtain current (and accurate) information
            about rumored security problems.

            To join the CERT-ADVISORY mailing list, send a message to
            CERT@CERT.SEI.CMU.EDU and ask to be added to the mailing
            list.  The material sent to this list also appears in the
            USENET newsgroup "".  Past advisories
            are available for anonymous FTP from the host
            CERT.SEI.CMU.EDU.  The 24-hour hotline number is (412) 268-

            The CERT/CC also maintains a CERT-TOOLS list to encourage
            the exchange of information on tools and techniques that
            increase the secure operation of Internet systems.  The
            CERT/CC does not review or endorse the tools described on
            the list.  To subscribe, send a message to CERT-TOOLS-
            REQUEST@CERT.SEI.CMU.EDU and ask to be added to the mailing

            The CERT/CC maintains other generally useful security
            information for anonymous FTP from CERT.SEI.CMU.EDU.  Get
            the README file for a list of what is available.

            For more information, contact:

               Software Engineering Institute
               Carnegie Mellon University
               Pittsburgh, PA  15213-3890

               (412) 268-7090

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  DDN Security Coordination Center

            For DDN users, the Security Coordination Center (SCC) serves
            a function similar to CERT.  The SCC is the DDN's clearing-
            house for host/user security problems and fixes, and works
            with the DDN Network Security Officer.  The SCC also
            distributes the DDN Security Bulletin, which communicates
            information on network and host security exposures, fixes,
            and concerns to security and management personnel at DDN
            facilities.  It is available online, via kermit or anonymous
            FTP, from the host NIC.DDN.MIL, in SCC:DDN-SECURITY-yy-
            nn.TXT (where "yy" is the year and "nn" is the bulletin
            number).  The SCC provides immediate assistance with DDN-
            related host security problems; call (800) 235-3155 (6:00
            a.m. to 5:00 p.m. Pacific Time) or send email to
            SCC@NIC.DDN.MIL.  For 24 hour coverage, call the MILNET
            Trouble Desk (800) 451-7413 or AUTOVON 231-1713.
  NIST Computer Security Resource and Response Center

            The National Institute of Standards and Technology (NIST)
            has responsibility within the U.S. Federal Government for
            computer science and technology activities.  NIST has played
            a strong role in organizing the CERT System and is now
            serving as the CERT System Secretariat.  NIST also operates
            a Computer Security Resource and Response Center (CSRC) to
            provide help and information regarding computer security
            events and incidents, as well as to raise awareness about
            computer security vulnerabilities.

            The CSRC team operates a 24-hour hotline, at (301) 975-5200.
            For individuals with access to the Internet, on-line
            publications and computer security information can be
            obtained via anonymous FTP from the host CSRC.NCSL.NIST.GOV
            (  NIST also operates a personal computer
            bulletin board that contains information regarding computer
            viruses as well as other aspects of computer security.  To
            access this board, set your modem to 300/1200/2400 BPS, 1
            stop bit, no parity, and 8-bit characters, and call (301)
            948-5717.  All users are given full access to the board
            immediately upon registering.

            NIST has produced several special publications related to
            computer security and computer viruses in particular; some
            of these publications are downloadable.  For further
            information, contact NIST at the following address:

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               Computer Security Resource and Response Center
               A-216 Technology
               Gaithersburg, MD 20899
               Telephone: (301) 975-3359
               Electronic Mail:
  DOE Computer Incident Advisory Capability (CIAC)

            CIAC is the Department of Energy's (DOE's) Computer Incident
            Advisory Capability.  CIAC is a four-person team of computer
            scientists from Lawrence Livermore National Laboratory
            (LLNL) charged with the primary responsibility of assisting
            DOE sites faced with computer security incidents (e.g.,
            intruder attacks, virus infections, worm attacks, etc.).
            This capability is available to DOE sites on a 24-hour-a-day

            CIAC was formed to provide a centralized response capability
            (including technical assistance), to keep sites informed of
            current events, to deal proactively with computer security
            issues, and to maintain liaisons with other response teams
            and agencies.  CIAC's charter is to assist sites (through
            direct technical assistance, providing information, or
            referring inquiries to other technical experts), serve as a
            clearinghouse for information about threats/known
            incidents/vulnerabilities, develop guidelines for incident
            handling, develop software for responding to
            events/incidents, analyze events and trends, conduct
            training and awareness activities, and alert and advise
            sites about vulnerabilities and potential attacks.

            CIAC's business hours phone number is (415) 422-8193 or FTS
            532-8193.  CIAC's e-mail address is CIAC@TIGER.LLNL.GOV.
  NASA Ames Computer Network Security Response Team

            The Computer Network Security Response Team (CNSRT) is NASA
            Ames Research Center's local version of the DARPA CERT.
            Formed in August of 1989, the team has a constituency that
            is primarily Ames users, but it is also involved in
            assisting other NASA Centers and federal agencies.  CNSRT
            maintains liaisons with the DOE's CIAC team and the DARPA
            CERT.  It is also a charter member of the CERT System.  The
            team may be reached by 24 hour pager at (415) 694-0571, or
            by electronic mail to CNSRT@AMES.ARC.NASA.GOV.

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RFC 1244                 Site Security Handbook                July 1991  DDN Management Bulletins

         The DDN Management Bulletin is distributed electronically by
         the DDN NIC under contract to the Defense Communications Agency
         (DCA).  It is a means of communicating official policy,
         procedures, and other information of concern to management
         personnel at DDN facilities.

         The DDN Security Bulletin is distributed electronically by the
         DDN SCC, also under contract to DCA, as a means of
         communicating information on network and host security
         exposures, fixes, and concerns to security and management
         personnel at DDN facilities.

         Anyone may join the mailing lists for these two bulletins by
         sending a message to NIC@NIC.DDN.MIL and asking to be placed on
         the mailing lists.  These messages are also posted to the
         USENET newsgroup "ddn.mgt-bulletin".  For additional
         information, see section 8.7.  System Administration List

         The SYSADM-LIST is a list pertaining exclusively to UNIX system
         administration.  Mail requests to be added to the list to
         SYSADM-LIST-REQUEST@SYSADMIN.COM.  Vendor Specific System Lists

         The SUN-SPOTS and SUN-MANAGERS lists are discussion groups for
         users and administrators of systems supplied by Sun
         Microsystems.  SUN-SPOTS is a fairly general list, discussing
         everything from hardware configurations to simple UNIX
         questions.  To subscribe, send a message to SUN-SPOTS-
         REQUEST@RICE.EDU.  This list is also available in the USENET
         newsgroup "comp.sys.sun".  SUN-MANAGERS is a discussion list
         for Sun system administrators and covers all aspects of Sun
         system administration.  To subscribe, send a message to SUN-

         The APOLLO list discusses the HP/Apollo system and its
         software.  To subscribe, send a message to APOLLO-
         REQUEST@UMIX.CC.UMICH.EDU.  APOLLO-L is a similar list which
         can be subscribed to by sending

            SUB APOLLO-L your full name


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         HPMINI-L pertains to the Hewlett-Packard 9000 series and HP/UX
         operating system.  To subscribe, send

            SUB HPMINI-L your full name


         INFO-IBMPC discusses IBM PCs and compatibles, as well as MS-
         DOS.  To subscribe, send a note to INFO-IBMPC-REQUEST@WSMR-

         There are numerous other mailing lists for nearly every popular
         computer or workstation in use today.  For a complete list,
         obtain the file "netinfo/interest-groups" via anonymous FTP
         from the host FTP.NISC.SRI.COM.  Professional Societies and Journals

         The IEEE Technical Committee on Security & Privacy publishes a
         quarterly magazine, "CIPHER".

            IEEE Computer Society,
            1730 Massachusetts Ave. N.W.
            Washington, DC  2036-1903

         The ACM SigSAC (Special Interest Group on Security, Audit, and
         Controls) publishes a quarterly magazine, "SIGSAC Review".

            Association for Computing Machinery
            11 West 42nd St.
            New York, N.Y.  10036

         The Information Systems Security Association publishes a
         quarterly magazine called "ISSA Access".

            Information Systems Security Association
            P.O. Box 9457
            Newport Beach, CA  92658

         "Computers and Security" is an "international journal for the
         professional involved with computer security, audit and
         control, and data integrity."

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            $266/year, 8 issues (1990)

            Elsevier Advanced Technology
            Journal Information Center
            655 Avenue of the Americas
            New York, NY 10010

         The "Data Security Letter" is published "to help data security
         professionals by providing inside information and knowledgable
         analysis of developments in computer and communications

            $690/year, 9 issues (1990)

            Data Security Letter
            P.O. Box 1593
            Palo Alto, CA 94302

   3.9.8  Problem Reporting Tools  Auditing

         Auditing is an important tool that can be used to enhance the
         security of your installation.  Not only does it give you a
         means of identifying who has accessed your system (and may have
         done something to it) but it also gives you an indication of
         how your system is being used (or abused) by authorized users
         and attackers alike.  In addition, the audit trail
         traditionally kept by computer systems can become an invaluable
         piece of evidence should your system be penetrated.
  Verify Security

            An audit trail shows how the system is being used from day
            to day.  Depending upon how your site audit log is
            configured, your log files should show a range of access
            attempts that can show what normal system usage should look
            like.  Deviation from that normal usage could be the result
            of penetration from an outside source using an old or stale
            user account.  Observing a deviation in logins, for example,
            could be your first indication that something unusual is
  Verify Software Configurations

            One of the ruses used by attackers to gain access to a
            system is by the insertion of a so-called Trojan Horse
            program.  A Trojan Horse program can be a program that does

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            something useful, or merely something interesting.  It
            always does something unexpected, like steal passwords or
            copy files without your knowledge [25].  Imagine a Trojan
            login program that prompts for username and password in the
            usual way, but also writes that information to a special
            file that the attacker can come back and read at will.
            Imagine a Trojan Editor program that, despite the file
            permissions you have given your files, makes copies of
            everything in your directory space without you knowing about

            This points out the need for configuration management of the
            software that runs on a system, not as it is being
            developed, but as it is in actual operation.  Techniques for
            doing this range from checking each command every time it is
            executed against some criterion (such as a cryptoseal,
            described above) or merely checking the date and time stamp
            of the executable.  Another technique might be to check each
            command in batch mode at midnight.  Tools

         COPS is a security tool for system administrators that checks
         for numerous common security problems on UNIX systems [27].
         COPS is a collection of shell scripts and C programs that can
         easily be run on almost any UNIX variant.  Among other things,
         it checks the following items and sends the results to the
         system administrator:

            - Checks "/dev/kmem" and other devices for world

            - Checks special or important files and directories for
              "bad" modes (world writable, etc.).

            - Checks for easily-guessed passwords.

            - Checks for duplicate user ids, invalid fields in the
              password file, etc..

            - Checks for duplicate group ids, invalid fields in the
              group file, etc..

            - Checks all users' home directories and their ".cshrc",
              ".login", ".profile", and ".rhosts" files for security

            - Checks all commands in the "/etc/rc" files and "cron"

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              files for world writability.

            - Checks for bad "root" paths, NFS file systems exported
              to the world, etc..

            - Includes an expert system that checks to see if a given
              user (usually "root") can be compromised, given that
              certain rules are true.

            - Checks for changes in the setuid status of programs on the

         The COPS package is available from the "comp.sources.unix"
         archive on "", and also from the UNIX-SW repository
         on the MILNET host "".

   3.9.9  Communication Among Administrators  Secure Operating Systems

         The following list of products and vendors is adapted from the
         National Computer Security Center's (NCSC) Evaluated Products
         List.  They represent those companies who have either received
         an evaluation from the NCSC or are in the process of a product
         evaluation.  This list is not complete, but it is
         representative of those operating systems and add on components
         available in the commercial marketplace.

         For a more detailed listing of the current products appearing
         in the NCSC EPL, contact the NCSC at:

            National Computer Security Center
            9800 Savage Road
            Fort George G. Meade, MD  20755-6000
            (301) 859-4458

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                                                  Version    Evaluation
Evaluated Product               Vendor            Evaluated  Class
Secure Communications           Honeywell Information    2.1         A1
Processor (SCOMP)               Systems, Inc.

Multics                         Honeywell Information    MR11.0      B2
                                Systems, Inc.

System V/MLS 1.1.2 on UNIX      AT&T                     1.1.2       B1
System V 3.1.1 on AT&T 3B2/500and 3B2/600

OS 1100                         Unisys Corp.             Security    B1
                                                         Release 1

MPE V/E                         Hewlett-Packard Computer G.03.04     C2
                                Systems Division

AOS/VS on MV/ECLIPSE series     Data General Corp.        7.60       C2

VM/SP or VM/SP HPO with CMS,    IBM Corp.                    5       C2

MVS/XA with RACF                IBM Corp.                 2.2,2.3    C2

AX/VMS                          Digital Equipment Corp.      4.3     C2

NOS                             Control Data Corp.         NOS
                                                           Security  C2
                                                       Eval Product

TOP SECRET                      CGA Software Products       3.0/163  C2
                                Group, Inc.

Access Control Facility 2       SKK, Inc.                    3.1.3   C2

UTX/32S                         Gould, Inc. Computer          1.0    C2
                                Systems Division

A Series MCP/AS with            Unisys Corp.                  3.7    C2
InfoGuard Security

Primos                          Prime Computer, Inc.    21.0.1DODC2A C2
Resource Access Control         IBM Corp.                     1.5    C1
Facility (RACF)

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                                                  Version      Candidate
Candidate Product            Vendor               Evaluated    Class
Boeing MLS LAN                  Boeing Aerospace                  A1 M1

Trusted XENIX                   Trusted Information
                                Systems, Inc.                     B2

VSLAN                           VERDIX Corp.                      B2

System V/MLS                    AT&T                              B1

VM/SP with RACF                 IBM Corp.              5/1.8.2    C2
Wang SVS/OS with CAP            Wang Laboratories, Inc.  1.0      C2  Obtaining Fixes for Known Problems

         It goes without saying that computer systems have bugs.  Even
         operating systems, upon which we depend for protection of our
         data, have bugs.  And since there are bugs, things can be
         broken, both maliciously and accidentally.  It is important
         that whenever bugs are discovered, a should fix be identified
         and implemented as soon as possible.  This should minimize any
         exposure caused by the bug in the first place.

         A corollary to the bug problem is: from whom do I obtain the
         fixes?  Most systems have some support from the manufacturer or
         supplier.  Fixes coming from that source tend to be implemented
         quickly after receipt.  Fixes for some problems are often
         posted on the network and are left to the system administrators
         to incorporate as they can.  The problem is that one wants to
         have faith that the fix will close the hole and not introduce
         any others.  We will tend to trust that the manufacturer's
         fixes are better than those that are posted on the net.  Sun Customer Warning System

         Sun Microsystems has established a Customer Warning System
         (CWS) for handling security incidents.  This is a formal
         process which includes:

            - Having a well advertised point of contact in Sun
              for reporting security problems.
            - Pro-actively alerting customers of worms, viruses,
              or other security holes that could affect their systems.
            - Distributing the patch (or work-around) as quickly
              as possible.

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         They have created an electronic mail address, SECURITY-
         ALERT@SUN.COM, which will enable customers to report security
         problems.  A voice-mail backup is available at (415) 688-9081.
         A "Security Contact" can be designated by each customer site;
         this person will be contacted by Sun in case of any new
         security problems.  For more information, contact your Sun
         representative.  Trusted Archive Servers

         Several sites on the Internet maintain large repositories of
         public-domain and freely distributable software, and make this
         material available for anonymous FTP.  This section describes
         some of the larger repositories.  Note that none of these
         servers implements secure checksums or anything else
         guaranteeing the integrity of their data.  Thus, the notion of
         "trust" should be taken as a somewhat limited definition.
  Sun Fixes on UUNET

            Sun Microsystems has contracted with UUNET Communications
            Services, Inc., to make fixes for bugs in Sun software
            available via anonymous FTP.  You can access these fixes by
            using the "ftp" command to connect to the host FTP.UU.NET.
            Then change into the directory "sun-dist/security", and
            obtain a directory listing.  The file "README" contains a
            brief description of what each file in this directory
            contains, and what is required to install the fix.
  Berkeley Fixes

            The University of California at Berkeley also makes fixes
            available via anonymous FTP; these fixes pertain primarily
            to the current release of BSD UNIX (currently, release 4.3).
            However, even if you are not running their software, these
            fixes are still important, since many vendors (Sun, DEC,
            Sequent, etc.) base their software on the Berkeley releases.

            The Berkeley fixes are available for anonymous FTP from the
            host UCBARPA.BERKELEY.EDU in the directory "4.3/ucb-fixes".
            The file "INDEX" in this directory describes what each file
            contains.  They are also available from UUNET (see section

            Berkeley also distributes new versions of "sendmail" and
            "named" from this machine.  New versions of these commands
            are stored in the "4.3" directory, usually in the files
            "sendmail.tar.Z" and "bind.tar.Z", respectively.

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  Simtel-20 and UUNET

            The two largest general-purpose software repositories on the
            Internet are the hosts WSMR-SIMTEL20.ARMY.MIL and

            WSMR-SIMTEL20.ARMY.MIL is a TOPS-20 machine operated by the
            U.S. Army at White Sands Missile Range (WSMR), New Mexico.
            The directory "pd2:<unix-c>" contains a large amount of UNIX
            software, primarily taken from the "comp.sources"
            newsgroups.  The directories "pd1:<msdos>" and
            "pd2:<msdos2>" contains software for IBM PC systems, and
            "pd3:<macintosh>" contains software for the Apple Macintosh.

            FTP.UU.NET is operated by UUNET Communications Services,
            Inc. in Falls Church, Virginia.  This company sells Internet
            and USENET access to sites all over the country (and
            internationally).  The software posted to the following
            USENET source newsgroups is stored here, in directories of
            the same name:


            Numerous other distributions, such as all the freely
            distributable Berkeley UNIX source code, Internet Request
            for Comments (RFCs), and so on are also stored on this

            Many vendors make fixes for bugs in their software available
            electronically, either via mailing lists or via anonymous
            FTP.  You should contact your vendor to find out if they
            offer this service, and if so, how to access it.  Some
            vendors that offer these services include Sun Microsystems
            (see above), Digital Equipment Corporation (DEC), the
            University of California at Berkeley (see above), and Apple
            Computer [5, CURRY].

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4.  Types of Security Procedures

4.1  System Security Audits

   Most businesses undergo some sort of annual financial auditing as a
   regular part of their business life.  Security audits are an
   important part of running any computing environment.  Part of the
   security audit should be a review of any policies that concern system
   security, as well as the mechanisms that are put in place to enforce

   4.1.1   Organize Scheduled Drills

      Although not something that would be done each day or week,
      scheduled drills may be conducted to determine if the procedures
      defined are adequate for the threat to be countered.  If your
      major threat is one of natural disaster, then a drill would be
      conducted to verify your backup and recovery mechanisms.  On the
      other hand, if your greatest threat is from external intruders
      attempting to penetrate your system, a drill might be conducted to
      actually try a penetration to observe the effect of the policies.

      Drills are a valuable way to test that your policies and
      procedures are effective.  On the other hand, drills can be time-
      consuming and disruptive to normal operations.  It is important to
      weigh the benefits of the drills against the possible time loss
      which may be associated with them.

   4.1.2  Test Procedures

      If the choice is made to not to use scheduled drills to examine
      your entire security procedure at one time, it is important to
      test individual procedures frequently.  Examine your backup
      procedure to make sure you can recover data from the tapes.  Check
      log files to be sure that information which is supposed to be
      logged to them is being logged to them, etc..

      When a security audit is mandated, great care should be used in
      devising tests of the security policy.  It is important to clearly
      identify what is being tested, how the test will be conducted, and
      results expected from the test.  This should all be documented and
      included in or as an adjunct to the security policy document

      It is important to test all aspects of the security policy, both
      procedural and automated, with a particular emphasis on the
      automated mechanisms used to enforce the policy.  Tests should be
      defined to ensure a comprehensive examination of policy features,

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      that is, if a test is defined to examine the user logon process,
      it should be explicitly stated that both valid and invalid user
      names and passwords will be used to demonstrate proper operation
      of the logon program.

      Keep in mind that there is a limit to the reasonableness of tests.
      The purpose of testing is to ensure confidence that the security
      policy is being correctly enforced, and not to "prove" the
      absoluteness of the system or policy.  The goal should be to
      obtain some assurance that the reasonable and credible controls
      imposed by your security policy are adequate.

4.2  Account Management Procedures

   Procedures to manage accounts are important in preventing
   unauthorized access to your system.  It is necessary to decide
   several things: Who may have an account on the system?  How long may
   someone have an account without renewing his or her request?  How do
   old accounts get removed from the system?  The answers to all these
   questions should be explicitly set out in the policy.

   In addition to deciding who may use a system, it may be important to
   determine what each user may use the system for (is personal use
   allowed, for example).  If you are connected to an outside network,
   your site or the network management may have rules about what the
   network may be used for.  Therefore, it is important for any security
   policy to define an adequate account management procedure for both
   administrators and users.  Typically, the system administrator would
   be responsible for creating and deleting user accounts and generally
   maintaining overall control of system use.  To some degree, account
   management is also the responsibility of each system user in the
   sense that the user should observe any system messages and events
   that may be indicative of a policy violation.  For example, a message
   at logon that indicates the date and time of the last logon should be
   reported by the user if it indicates an unreasonable time of last

4.3  Password Management Procedures

   A policy on password management may be important if your site wishes
   to enforce secure passwords.  These procedures may range from asking
   or forcing users to change their passwords occasionally to actively
   attempting to break users' passwords and then informing the user of
   how easy it was to do.  Another part of password management policy
   covers who may distribute passwords - can users give their passwords
   to other users?

   Section 2.3 discusses some of the policy issues that need to be

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   decided for proper password management.  Regardless of the policies,
   password management procedures need to be carefully setup to avoid
   disclosing passwords.  The choice of initial passwords for accounts
   is critical.  In some cases, users may never login to activate an
   account; thus, the choice of the initial password should not be
   easily guessed.  Default passwords should never be assigned to
   accounts: always create new passwords for each user.  If there are
   any printed lists of passwords, these should be kept off-line in
   secure locations; better yet, don't list passwords.

   4.3.1  Password Selection

      Perhaps the most vulnerable part of any computer system is the
      account password.  Any computer system, no matter how secure it is
      from network or dial-up attack, Trojan horse programs, and so on,
      can be fully exploited by an intruder if he or she can gain access
      via a poorly chosen password.  It is important to define a good
      set of rules for password selection, and distribute these rules to
      all users.  If possible, the software which sets user passwords
      should be modified to enforce as many of the rules as possible.

      A sample set of guidelines for password selection is shown below:

         - DON'T use your login name in any form (as-is,
           reversed, capitalized, doubled, etc.).

         - DON'T use your first, middle, or last name in any form.

         - DON'T use your spouse's or child's name.

         - DON'T use other information easily obtained about you.
           This includes license plate numbers, telephone numbers,
           social security numbers, the make of your automobile,
           the name of the street you live on, etc..

         - DON'T use a password of all digits, or all the same

         - DON'T use a word contained in English or foreign
           language dictionaries, spelling lists, or other
           lists of words.

         - DON'T use a password shorter than six characters.

         - DO use a password with mixed-case alphabetics.

         - DO use a password with non-alphabetic characters (digits
           or punctuation).

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         - DO use a password that is easy to remember, so you don't
           have to write it down.

         - DO use a password that you can type quickly, without
           having to look at the keyboard.

      Methods of selecting a password which adheres to these guidelines

         - Choose a line or two from a song or poem, and use the
           first letter of each word.

         - Alternate between one consonant and one or two vowels, up
           to seven or eight characters.  This provides nonsense
           words which are usually pronounceable, and thus easily

         - Choose two short words and concatenate them together with
           a punctuation character between them.

      Users should also be told to change their password periodically,
      usually every three to six months.  This makes sure that an
      intruder who has guessed a password will eventually lose access,
      as well as invalidating any list of passwords he/she may have
      obtained.  Many systems enable the system administrator to force
      users to change their passwords after an expiration period; this
      software should be enabled if your system supports it [5, CURRY].

      Some systems provide software which forces users to change their
      passwords on a regular basis.  Many of these systems also include
      password generators which provide the user with a set of passwords
      to choose from.  The user is not permitted to make up his or her
      own password.  There are arguments both for and against systems
      such as these.  On the one hand, by using generated passwords,
      users are prevented from selecting insecure passwords.  On the
      other hand, unless the generator is good at making up easy to
      remember passwords, users will begin writing them down in order to
      remember them.

   4.3.2  Procedures for Changing Passwords

      How password changes are handled is important to keeping passwords
      secure.  Ideally, users should be able to change their own
      passwords on-line.  (Note that password changing programs are a
      favorite target of intruders.  See section 4.4 on configuration
      management for further information.)

      However, there are exception cases which must be handled

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      carefully.  Users may forget passwords and not be able to get onto
      the system.  The standard procedure is to assign the user a new
      password.  Care should be taken to make sure that the real person
      is requesting the change and gets the new password.  One common
      trick used by intruders is to call or message to a system
      administrator and request a new password. Some external form of
      verification should be used before the password is assigned.  At
      some sites, users are required to show up in person with ID.

      There may also be times when many passwords need to be changed.
      If a system is compromised by an intruder, the intruder may be
      able to steal a password file and take it off the system.  Under
      these circumstances, one course of action is to change all
      passwords on the system.  Your site should have procedures for how
      this can be done quickly and efficiently.  What course you choose
      may depend on the urgency of the problem.  In the case of a known
      attack with damage, you may choose to forcibly disable all
      accounts and assign users new passwords before they come back onto
      the system.  In some places, users are sent a message telling them
      that they should change their passwords, perhaps within a certain
      time period.  If the password isn't changed before the time period
      expires, the account is locked.

      Users should be aware of what the standard procedure is for
      passwords when a security event has occurred.  One well-known
      spoof reported by the Computer Emergency Response Team (CERT)
      involved messages sent to users, supposedly from local system
      administrators, requesting them to immediately change their
      password to a new value provided in the message [24].  These
      messages were not from the administrators, but from intruders
      trying to steal accounts.  Users should be warned to immediately
      report any suspicious requests such as this to site

4.4  Configuration Management Procedures

   Configuration management is generally applied to the software
   development process.  However, it is certainly applicable in a
   operational sense as well.  Consider that the since many of the
   system level programs are intended to enforce the security policy, it
   is important that these be "known" as correct.  That is, one should
   not allow system level programs (such as the operating system, etc.)
   to be changed arbitrarily.  At very least, the procedures should
   state who is authorized to make changes to systems, under what
   circumstances, and how the changes should be documented.

   In some environments, configuration management is also desirable as
   applied to physical configuration of equipment.  Maintaining valid

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   and authorized hardware configuration should be given due
   consideration in your security policy.

   4.4.1  Non-Standard Configurations

      Occasionally, it may be beneficial to have a slightly non-standard
      configuration in order to thwart the "standard" attacks used by
      some intruders.  The non-standard parts of the configuration might
      include different password encryption algorithms, different
      configuration file locations, and rewritten or functionally
      limited system commands.

      Non-standard configurations, however, also have their drawbacks.
      By changing the "standard" system, these modifications make
      software maintenance more difficult by requiring extra
      documentation to be written, software modification after operating
      system upgrades, and, usually, someone with special knowledge of
      the changes.

      Because of the drawbacks of non-standard configurations, they are
      often only used in environments with a "firewall" machine (see
      section 3.9.1).  The firewall machine is modified in non-standard
      ways since it is susceptible to attack, while internal systems
      behind the firewall are left in their standard configurations.

5.  Incident Handling

5.1  Overview

   This section of the document will supply some guidance to be applied
   when a computer security event is in progress on a machine, network,
   site, or multi-site environment.  The operative philosophy in the
   event of a breach of computer security, whether it be an external
   intruder attack or a disgruntled employee, is to plan for adverse
   events in advance.  There is no substitute for creating contingency
   plans for the types of events described above.

   Traditional computer security, while quite important in the overall
   site security plan, usually falls heavily on protecting systems from
   attack, and perhaps monitoring systems to detect attacks.  Little
   attention is usually paid for how to actually handle the attack when
   it occurs.  The result is that when an attack is in progress, many
   decisions are made in haste and can be damaging to tracking down the
   source of the incident, collecting evidence to be used in prosecution
   efforts, preparing for the recovery of the system, and protecting the
   valuable data contained on the system.

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   5.1.1  Have a Plan to Follow in Case of an Incident

      Part of handling an incident is being prepared to respond before
      the incident occurs.  This includes establishing a suitable level
      of protections, so that if the incident becomes severe, the damage
      which can occur is limited.  Protection includes preparing
      incident handling guidelines or a contingency response plan for
      your organization or site.  Having written plans eliminates much
      of the ambiguity which occurs during an incident, and will lead to
      a more appropriate and thorough set of responses.  Second, part of
      protection is preparing a method of notification, so you will know
      who to call and the relevant phone numbers.  It is important, for
      example, to conduct "dry runs," in which your computer security
      personnel, system administrators, and managers simulate handling
      an incident.

      Learning to respond efficiently to an incident is important for
      numerous reasons.  The most important benefit is directly to human
      beings--preventing loss of human life.  Some computing systems are
      life critical systems, systems on which human life depends (e.g.,
      by controlling some aspect of life-support in a hospital or
      assisting air traffic controllers).

      An important but often overlooked benefit is an economic one.
      Having both technical and managerial personnel respond to an
      incident requires considerable resources, resources which could be
      utilized more profitably if an incident did not require their
      services.  If these personnel are trained to handle an incident
      efficiently, less of their time is required to deal with that

      A third benefit is protecting classified, sensitive, or
      proprietary information.  One of the major dangers of a computer
      security incident is that information may be irrecoverable.
      Efficient incident handling minimizes this danger.  When
      classified information is involved, other government regulations
      may apply and must be integrated into any plan for incident

      A fourth benefit is related to public relations.  News about
      computer security incidents tends to be damaging to an
      organization's stature among current or potential clients.
      Efficient incident handling minimizes the potential for negative

      A final benefit of efficient incident handling is related to legal
      issues.  It is possible that in the near future organizations may
      be sued because one of their nodes was used to launch a network

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      attack.  In a similar vein, people who develop patches or
      workarounds may be sued if the patches or workarounds are
      ineffective, resulting in damage to systems, or if the patches or
      workarounds themselves damage systems.  Knowing about operating
      system vulnerabilities and patterns of attacks and then taking
      appropriate measures is critical to circumventing possible legal

   5.1.2  Order of Discussion in this Session Suggests an Order for
          a Plan

      This chapter is arranged such that a list may be generated from
      the Table of Contents to provide a starting point for creating a
      policy for handling ongoing incidents.  The main points to be
      included in a policy for handling incidents are:

         o Overview (what are the goals and objectives in handling the
         o Evaluation (how serious is the incident).
         o Notification (who should be notified about the incident).
         o Response (what should the response to the incident be).
         o Legal/Investigative (what are the legal and prosecutorial
           implications of the incident).
         o Documentation Logs (what records should be kept from before,
           during, and after the incident).

      Each of these points is important in an overall plan for handling
      incidents.  The remainder of this chapter will detail the issues
      involved in each of these topics, and provide some guidance as to
      what should be included in a site policy for handling incidents.

      5.1.3  Possible Goals and Incentives for Efficient Incident

      As in any set of pre-planned procedures, attention must be placed
      on a set of goals to be obtained in handling an incident.  These
      goals will be placed in order of importance depending on the site,
      but one such set of goals might be:

         Assure integrity of (life) critical systems.
         Maintain and restore data.
         Maintain and restore service.
         Figure out how it happened.
         Avoid escalation and further incidents.
         Avoid negative publicity.
         Find out who did it.
         Punish the attackers.

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      It is important to prioritize actions to be taken during an
      incident well in advance of the time an incident occurs.
      Sometimes an incident may be so complex that it is impossible to
      do everything at once to respond to it; priorities are essential.
      Although priorities will vary from institution-to-institution, the
      following suggested priorities serve as a starting point for
      defining an organization's response:

         o Priority one -- protect human life and people's
           safety; human life always has precedence over all
           other considerations.

         o Priority two -- protect classified and/or sensitive
           data (as regulated by your site or by government

         o Priority three -- protect other data, including
           proprietary, scientific, managerial and other data,
           because loss of data is costly in terms of resources.

         o Priority four -- prevent damage to systems (e.g., loss
           or alteration of system files, damage to disk drives,
           etc.); damage to systems can result in costly down
           time and recovery.

         o Priority five -- minimize disruption of computing
           resources; it is better in many cases to shut a system
           down or disconnect from a network than to risk damage
           to data or systems.

      An important implication for defining priorities is that once
      human life and national security considerations have been
      addressed, it is generally more important to save data than system
      software and hardware.  Although it is undesirable to have any
      damage or loss during an incident, systems can be replaced; the
      loss or compromise of data (especially classified data), however,
      is usually not an acceptable outcome under any circumstances.

      Part of handling an incident is being prepared to respond before
      the incident occurs.  This includes establishing a suitable level
      of protections so that if the incident becomes severe, the damage
      which can occur is limited.  Protection includes preparing
      incident handling guidelines or a contingency response plan for
      your organization or site.  Written plans eliminate much of the
      ambiguity which occurs during an incident, and will lead to a more
      appropriate and thorough set of responses.  Second, part of
      protection is preparing a method of notification so you will know
      who to call and how to contact them.  For example, every member of

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      the Department of Energy's CIAC Team carries a card with every
      other team member's work and home phone numbers, as well as pager
      numbers.  Third, your organization or site should establish backup
      procedures for every machine and system.  Having backups
      eliminates much of the threat of even a severe incident, since
      backups preclude serious data loss.  Fourth, you should set up
      secure systems.  This involves eliminating vulnerabilities,
      establishing an effective password policy, and other procedures,
      all of which will be explained later in this document.  Finally,
      conducting training activities is part of protection.  It is
      important, for example, to conduct "dry runs," in which your
      computer security personnel, system administrators, and managers
      simulate handling an incident.

   5.1.4  Local Policies and Regulations Providing Guidance

      Any plan for responding to security incidents should be guided by
      local policies and regulations.  Government and private sites that
      deal with classified material have specific rules that they must

      The policies your site makes about how it responds to incidents
      (as discussed in sections 2.4 and 2.5) will shape your response.
      For example, it may make little sense to create mechanisms to
      monitor and trace intruders if your site does not plan to take
      action against the intruders if they are caught.  Other
      organizations may have policies that affect your plans.  Telephone
      companies often release information about telephone traces only to
      law enforcement agencies.

      Section 5.5 also notes that if any legal action is planned, there
      are specific guidelines that must be followed to make sure that
      any information collected can be used as evidence.

5.2  Evaluation

   5.2.1  Is It Real?

      This stage involves determining the exact problem.  Of course
      many, if not most, signs often associated with virus infections,
      system intrusions, etc., are simply anomalies such as hardware
      failures.  To assist in identifying whether there really is an
      incident, it is usually helpful to obtain and use any detection
      software which may be available.  For example, widely available
      software packages can greatly assist someone who thinks there may
      be a virus in a Macintosh computer.  Audit information is also
      extremely useful, especially in determining whether there is a
      network attack.  It is extremely important to obtain a system

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      snapshot as soon as one suspects that something is wrong.  Many
      incidents cause a dynamic chain of events to occur, and an initial
      system snapshot may do more good in identifying the problem and
      any source of attack than most other actions which can be taken at
      this stage.  Finally, it is important to start a log book.
      Recording system events, telephone conversations, time stamps,
      etc., can lead to a more rapid and systematic identification of
      the problem, and is the basis for subsequent stages of incident

      There are certain indications or "symptoms" of an incident which
      deserve special attention:

         o System crashes.
         o New user accounts (e.g., the account RUMPLESTILTSKIN
           has unexplainedly been created), or high activity on
           an account that has had virtually no activity for
         o New files (usually with novel or strange file names,
           such as data.xx or k).
         o Accounting discrepancies (e.g., in a UNIX system you
           might notice that the accounting file called
           /usr/admin/lastlog has shrunk, something that should
           make you very suspicious that there may be an
         o Changes in file lengths or dates (e.g., a user should
           be suspicious if he/she observes that the .EXE files in
           an MS DOS computer have unexplainedly grown
           by over 1800 bytes).
         o Attempts to write to system (e.g., a system manager
           notices that a privileged user in a VMS system is
           attempting to alter RIGHTSLIST.DAT).
         o Data modification or deletion (e.g., files start to
         o Denial of service (e.g., a system manager and all
           other users become locked out of a UNIX system, which
           has been changed to single user mode).
         o Unexplained, poor system performance (e.g., system
           response time becomes unusually slow).
         o Anomalies (e.g., "GOTCHA" is displayed on a display
           terminal or there are frequent unexplained "beeps").
         o Suspicious probes (e.g., there are numerous
           unsuccessful login attempts from another node).
         o Suspicious browsing (e.g., someone becomes a root user
           on a UNIX system and accesses file after file in one
           user's account, then another's).

      None of these indications is absolute "proof" that an incident is

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      occurring, nor are all of these indications normally observed when
      an incident occurs.  If you observe any of these indications,
      however, it is important to suspect that an incident might be
      occurring, and act accordingly.  There is no formula for
      determining with 100 percent accuracy that an incident is
      occurring (possible exception: when a virus detection package
      indicates that your machine has the nVIR virus and you confirm
      this by examining contents of the nVIR resource in your Macintosh
      computer, you can be very certain that your machine is infected).
      It is best at this point to collaborate with other technical and
      computer security personnel to make a decision as a group about
      whether an incident is occurring.

   5.2.2  Scope

      Along with the identification of the incident is the evaluation of
      the scope and impact of the problem.  It is important to correctly
      identify the boundaries of the incident in order to effectively
      deal with it.  In addition, the impact of an incident will
      determine its priority in allocating resources to deal with the
      event.  Without an indication of the scope and impact of the
      event, it is difficult to determine a correct response.

      In order to identify the scope and impact, a set of criteria
      should be defined which is appropriate to the site and to the type
      of connections available.  Some of the issues are:

         o Is this a multi-site incident?
         o Are many computers at your site effected by this
         o Is sensitive information involved?
         o What is the entry point of the incident (network,
           phone line, local terminal, etc.)?
         o Is the press involved?
         o What is the potential damage of the incident?
         o What is the estimated time to close out the incident?
         o What resources could be required
           to handle the incident?

5.3  Possible Types of Notification

   When you have confirmed that an incident is occurring, the
   appropriate personnel must be notified.  Who and how this
   notification is achieved is very important in keeping the event under
   control both from a technical and emotional standpoint.

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   5.3.1  Explicit

      First of all, any notification to either local or off-site
      personnel must be explicit.  This requires that any statement (be
      it an electronic mail message, phone call, or fax) provides
      information about the incident that is clear, concise, and fully
      qualified.  When you are notifying others that will help you to
      handle an event, a "smoke screen" will only divide the effort and
      create confusion.  If a division of labor is suggested, it is
      helpful to provide information to each section about what is being
      accomplished in other efforts.  This will not only reduce
      duplication of effort, but allow people working on parts of the
      problem to know where to obtain other information that would help
      them resolve a part of the incident.

   5.3.2  Factual

      Another important consideration when communicating about the
      incident is to be factual.  Attempting to hide aspects of the
      incident by providing false or incomplete information may not only
      prevent a successful resolution to the incident, but may even
      worsen the situation.  This is especially true when the press is
      involved.  When an incident severe enough to gain press attention
      is ongoing, it is likely that any false information you provide
      will not be substantiated by other sources.  This will reflect
      badly on the site and may create enough ill-will between the site
      and the press to damage the site's public relations.

   5.3.3  Choice of Language

      The choice of language used when notifying people about the
      incident can have a profound effect on the way that information is
      received.  When you use emotional or inflammatory terms, you raise
      the expectations of damage and negative outcomes of the incident.
      It is important to remain calm both in written and spoken

      Another issue associated with the choice of language is the
      notification to non-technical or off-site personnel.  It is
      important to accurately describe the incident without undue alarm
      or confusing messages.  While it is more difficult to describe the
      incident to a non-technical audience, it is often more important.
      A non-technical description may be required for upper-level
      management, the press, or law enforcement liaisons.  The
      importance of these notifications cannot be underestimated and may
      make the difference between handling the incident properly and
      escalating to some higher level of damage.

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   5.3.4  Notification of Individuals

         o Point of Contact (POC) people (Technical, Administrative,
           Response Teams, Investigative, Legal, Vendors, Service
           providers), and which POCs are visible to whom.
         o Wider community (users).
         o Other sites that might be affected.

      Finally, there is the question of who should be notified during
      and after the incident.  There are several classes of individuals
      that need to be considered for notification.  These are the
      technical personnel, administration, appropriate response teams
      (such as CERT or CIAC), law enforcement, vendors, and other
      service providers.  These issues are important for the central
      point of contact, since that is the person responsible for the
      actual notification of others (see section 5.3.6 for further
      information).  A list of people in each of these categories is an
      important time saver for the POC during an incident.  It is much
      more difficult to find an appropriate person during an incident
      when many urgent events are ongoing.

      In addition to the people responsible for handling part of the
      incident, there may be other sites affected by the incident (or
      perhaps simply at risk from the incident).  A wider community of
      users may also benefit from knowledge of the incident.  Often, a
      report of the incident once it is closed out is appropriate for
      publication to the wider user community.

   5.3.5  Public Relations - Press Releases

      One of the most important issues to consider is when, who, and how
      much to release to the general public through the press.  There
      are many issues to consider when deciding this particular issue.
      First and foremost, if a public relations office exists for the
      site, it is important to use this office as liaison to the press.
      The public relations office is trained in the type and wording of
      information released, and will help to assure that the image of
      the site is protected during and after the incident (if possible).
      A public relations office has the advantage that you can
      communicate candidly with them, and provide a buffer between the
      constant press attention and the need of the POC to maintain
      control over the incident.

      If a public relations office is not available, the information
      released to the press must be carefully considered.  If the
      information is sensitive, it may be advantageous to provide only
      minimal or overview information to the press.  It is quite
      possible that any information provided to the press will be

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      quickly reviewed by the perpetrator of the incident.  As a
      contrast to this consideration, it was discussed above that
      misleading the press can often backfire and cause more damage than
      releasing sensitive information.

      While it is difficult to determine in advance what level of detail
      to provide to the press, some guidelines to keep in mind are:

         o Keep the technical level of detail low.  Detailed
           information about the incident may provide enough
           information for copy-cat events or even damage the
           site's ability to prosecute once the event is over.
         o Keep the speculation out of press statements.
           Speculation of who is causing the incident or the
           motives are very likely to be in error and may cause
           an inflamed view of the incident.
         o Work with law enforcement professionals to assure that
           evidence is protected.  If prosecution is involved,
           assure that the evidence collected is not divulged to
           the press.
         o Try not to be forced into a press interview before you are
           prepared.  The popular press is famous for the "2am"
           interview, where the hope is to catch the interviewee off
           guard and obtain information otherwise not available.
         o Do not allow the press attention to detract from the
           handling of the event.  Always remember that the successful
           closure of an incident is of primary importance.

   5.3.6  Who Needs to Get Involved?

      There now exists a number of incident response teams (IRTs) such
      as the CERT and the CIAC. (See sections and
      Teams exists for many major government agencies and large
      corporations.  If such a team is available for your site, the
      notification of this team should be of primary importance during
      the early stages of an incident.  These teams are responsible for
      coordinating computer security incidents over a range of sites and
      larger entities.  Even if the incident is believed to be contained
      to a single site, it is possible that the information available
      through a response team could help in closing out the incident.

      In setting up a site policy for incident handling, it may be
      desirable to create an incident handling team (IHT), much like
      those teams that already exist, that will be responsible for
      handling computer security incidents for the site (or
      organization).  If such a team is created, it is essential that
      communication lines be opened between this team and other IHTs.
      Once an incident is under way, it is difficult to open a trusted

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      dialogue between other IHTs if none has existed before.

5.4  Response

   A major topic still untouched here is how to actually respond to an
   event.  The response to an event will fall into the general
   categories of containment, eradication, recovery, and follow-up.


      The purpose of containment is to limit the extent of an attack.
      For example, it is important to limit the spread of a worm attack
      on a network as quickly as possible.  An essential part of
      containment is decision making (i.e., determining whether to shut
      a system down, to disconnect from a network, to monitor system or
      network activity, to set traps, to disable functions such as
      remote file transfer on a UNIX system, etc.).  Sometimes this
      decision is trivial; shut the system down if the system is
      classified or sensitive, or if proprietary information is at risk!
      In other cases, it is worthwhile to risk having some damage to the
      system if keeping the system up might enable you to identify an

      The third stage, containment, should involve carrying out
      predetermined procedures.  Your organization or site should, for
      example, define acceptable risks in dealing with an incident, and
      should prescribe specific actions and strategies accordingly.
      Finally, notification of cognizant authorities should occur during
      this stage.


      Once an incident has been detected, it is important to first think
      about containing the incident.  Once the incident has been
      contained, it is now time to eradicate the cause.  Software may be
      available to help you in this effort.  For example, eradication
      software is available to eliminate most viruses which infect small
      systems.  If any bogus files have been created, it is time to
      delete them at this point.  In the case of virus infections, it is
      important to clean and reformat any disks containing infected
      files.  Finally, ensure that all backups are clean.  Many systems
      infected with viruses become periodically reinfected simply
      because people do not systematically eradicate the virus from


      Once the cause of an incident has been eradicated, the recovery

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      phase defines the next stage of action.  The goal of recovery is
      to return the system to normal.  In the case of a network-based
      attack, it is important to install patches for any operating
      system vulnerability which was exploited.


      One of the most important stages of responding to incidents is
      also the most often omitted---the follow-up stage.  This stage is
      important because it helps those involved in handling the incident
      develop a set of "lessons learned" (see section 6.3) to improve
      future performance in such situations.  This stage also provides
      information which justifies an organization's computer security
      effort to management, and yields information which may be
      essential in legal proceedings.

      The most important element of the follow-up stage is performing a
      postmortem analysis.  Exactly what happened, and at what times?
      How well did the staff involved with the incident perform?  What
      kind of information did the staff need quickly, and how could they
      have gotten that information as soon as possible?  What would the
      staff do differently next time?  A follow-up report is valuable
      because it provides a reference to be used in case of other
      similar incidents.  Creating a formal chronology of events
      (including time stamps) is also important for legal reasons.
      Similarly, it is also important to as quickly obtain a monetary
      estimate of the amount of damage the incident caused in terms of
      any loss of software and files, hardware damage, and manpower
      costs to restore altered files, reconfigure affected systems, and
      so forth.  This estimate may become the basis for subsequent
      prosecution activity by the FBI, the U.S. Attorney General's
      Office, etc..

   5.4.1  What Will You Do?

      o Restore control.
      o Relation to policy.
      o Which level of service is needed?
      o Monitor activity.
      o Constrain or shut down system.

   5.4.2  Consider Designating a "Single Point of Contact"

      When an incident is under way, a major issue is deciding who is in
      charge of coordinating the activity of the multitude of players.
      A major mistake that can be made is to have a number of "points of
      contact" (POC) that are not pulling their efforts together.  This
      will only add to the confusion of the event, and will probably

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      lead to additional confusion and wasted or ineffective effort.

      The single point of contact may or may not be the person "in
      charge" of the incident.  There are two distinct rolls to fill
      when deciding who shall be the point of contact and the person in
      charge of the incident.  The person in charge will make decisions
      as to the interpretation of policy applied to the event.  The
      responsibility for the handling of the event falls onto this
      person.  In contrast, the point of contact must coordinate the
      effort of all the parties involved with handling the event.

      The point of contact must be a person with the technical expertise
      to successfully coordinate the effort of the system managers and
      users involved in monitoring and reacting to the attack.  Often
      the management structure of a site is such that the administrator
      of a set of resources is not a technically competent person with
      regard to handling the details of the operations of the computers,
      but is ultimately responsible for the use of these resources.

      Another important function of the POC is to maintain contact with
      law enforcement and other external agencies (such as the CIA, DoD,
      U.S.  Army, or others) to assure that multi-agency involvement

      Finally, if legal action in the form of prosecution is involved,
      the POC may be able to speak for the site in court.  The
      alternative is to have multiple witnesses that will be hard to
      coordinate in a legal sense, and will weaken any case against the
      attackers.  A single POC may also be the single person in charge
      of evidence collected, which will keep the number of people
      accounting for evidence to a minimum.  As a rule of thumb, the
      more people that touch a potential piece of evidence, the greater
      the possibility that it will be inadmissible in court.  The
      section below (Legal/Investigative) will provide more details for
      consideration on this topic.

5.5  Legal/Investigative

   5.5.1  Establishing Contacts with Investigative Agencies

      It is important to establish contacts with personnel from
      investigative agencies such as the FBI and Secret Service as soon
      as possible, for several reasons.  Local law enforcement and local
      security offices or campus police organizations should also be
      informed when appropriate.  A primary reason is that once a major
      attack is in progress, there is little time to call various
      personnel in these agencies to determine exactly who the correct
      point of contact is.  Another reason is that it is important to

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      cooperate with these agencies in a manner that will foster a good
      working relationship, and that will be in accordance with the
      working procedures of these agencies.  Knowing the working
      procedures in advance and the expectations of your point of
      contact is a big step in this direction.  For example, it is
      important to gather evidence that will be admissible in a court of
      law.  If you don't know in advance how to gather admissible
      evidence, your efforts to collect evidence during an incident are
      likely to be of no value to the investigative agency with which
      you deal.  A final reason for establishing contacts as soon as
      possible is that it is impossible to know the particular agency
      that will assume jurisdiction in any given incident.  Making
      contacts and finding the proper channels early will make
      responding to an incident go considerably more smoothly.

      If your organization or site has a legal counsel, you need to
      notify this office soon after you learn that an incident is in
      progress.  At a minimum, your legal counsel needs to be involved
      to protect the legal and financial interests of your site or
      organization.  There are many legal and practical issues, a few of
      which are:

         1. Whether your site or organization is willing to risk
            negative publicity or exposure to cooperate with legal
            prosecution efforts.

         2. Downstream liability--if you leave a compromised system
            as is so it can be monitored and another computer is damaged
            because the attack originated from your system, your site or
            organization may be liable for damages incurred.

         3. Distribution of information--if your site or organization
            distributes information about an attack in which another
            site or organization may be involved or the vulnerability
            in a product that may affect ability to market that
            product, your site or organization may again be liable
            for any damages (including damage of reputation).

         4. Liabilities due to monitoring--your site or organization
            may be sued if users at your site or elsewhere discover
            that your site is monitoring account activity without
            informing users.

      Unfortunately, there are no clear precedents yet on the
      liabilities or responsibilities of organizations involved in a
      security incident or who might be involved in supporting an
      investigative effort.  Investigators will often encourage
      organizations to help trace and monitor intruders -- indeed, most

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      investigators cannot pursue computer intrusions without extensive
      support from the organizations involved.  However, investigators
      cannot provide protection from liability claims, and these kinds
      of efforts may drag out for months and may take lots of effort.

      On the other side, an organization's legal council may advise
      extreme caution and suggest that tracing activities be halted and
      an intruder shut out of the system.  This in itself may not
      provide protection from liability, and may prevent investigators
      from identifying anyone.

      The balance between supporting investigative activity and limiting
      liability is tricky; you'll need to consider the advice of your
      council and the damage the intruder is causing (if any) in making
      your decision about what to do during any particular incident.

      Your legal counsel should also be involved in any decision to
      contact investigative agencies when an incident occurs at your
      site.  The decision to coordinate efforts with investigative
      agencies is most properly that of your site or organization.
      Involving your legal counsel will also foster the multi-level
      coordination between your site and the particular investigative
      agency involved which in turn results in an efficient division of
      labor.  Another result is that you are likely to obtain guidance
      that will help you avoid future legal mistakes.

      Finally, your legal counsel should evaluate your site's written
      procedures for responding to incidents.  It is essential to obtain
      a "clean bill of health" from a legal perspective before you
      actually carry out these procedures.

   5.5.2  Formal and Informal Legal Procedures

      One of the most important considerations in dealing with
      investigative agencies is verifying that the person who calls
      asking for information is a legitimate representative from the
      agency in question.  Unfortunately, many well intentioned people
      have unknowingly leaked sensitive information about incidents,
      allowed unauthorized people into their systems, etc., because a
      caller has masqueraded as an FBI or Secret Service agent.  A
      similar consideration is using a secure means of communication.
      Because many network attackers can easily reroute electronic mail,
      avoid using electronic mail to communicate with other agencies (as
      well as others dealing with the incident at hand).  Non-secured
      phone lines (e.g., the phones normally used in the business world)
      are also frequent targets for tapping by network intruders, so be

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      There is no established set of rules for responding to an incident
      when the U.S. Federal Government becomes involved.  Except by
      court order, no agency can force you to monitor, to disconnect
      from the network, to avoid telephone contact with the suspected
      attackers, etc..  As discussed in section 5.5.1, you should
      consult the matter with your legal counsel, especially before
      taking an action that your organization has never taken.  The
      particular agency involved may ask you to leave an attacked
      machine on and to monitor activity on this machine, for example.
      Your complying with this request will ensure continued cooperation
      of the agency--usually the best route towards finding the source
      of the network attacks and, ultimately, terminating these attacks.
      Additionally, you may need some information or a favor from the
      agency involved in the incident.  You are likely to get what you
      need only if you have been cooperative.  Of particular importance
      is avoiding unnecessary or unauthorized disclosure of information
      about the incident, including any information furnished by the
      agency involved.  The trust between your site and the agency
      hinges upon your ability to avoid compromising the case the agency
      will build; keeping "tight lipped" is imperative.

      Sometimes your needs and the needs of an investigative agency will
      differ.  Your site may want to get back to normal business by
      closing an attack route, but the investigative agency may want you
      to keep this route open.  Similarly, your site may want to close a
      compromised system down to avoid the possibility of negative
      publicity, but again the investigative agency may want you to
      continue monitoring.  When there is such a conflict, there may be
      a complex set of tradeoffs (e.g., interests of your site's
      management, amount of resources you can devote to the problem,
      jurisdictional boundaries, etc.).  An important guiding principle
      is related to what might be called "Internet citizenship" [22,
      IAB89, 23] and its responsibilities.  Your site can shut a system
      down, and this will relieve you of the stress, resource demands,
      and danger of negative exposure.  The attacker, however, is likely
      to simply move on to another system, temporarily leaving others
      blind to the attacker's intention and actions until another path
      of attack can be detected.  Providing that there is no damage to
      your systems and others, the most responsible course of action is
      to cooperate with the participating agency by leaving your
      compromised system on.  This will allow monitoring (and,
      ultimately, the possibility of terminating the source of the
      threat to systems just like yours).  On the other hand, if there
      is damage to computers illegally accessed through your system, the
      choice is more complicated: shutting down the intruder may prevent
      further damage to systems, but might make it impossible to track
      down the intruder.  If there has been damage, the decision about
      whether it is important to leave systems up to catch the intruder

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      should involve all the organizations effected.  Further
      complicating the issue of network responsibility is the
      consideration that if you do not cooperate with the agency
      involved, you will be less likely to receive help from that agency
      in the future.

5.6  Documentation Logs

   When you respond to an incident, document all details related to the
   incident.  This will provide valuable information to yourself and
   others as you try to unravel the course of events.  Documenting all
   details will ultimately save you time.  If you don't document every
   relevant phone call, for example, you are likely to forget a good
   portion of information you obtain, requiring you to contact the
   source of information once again.  This wastes yours and others'
   time, something you can ill afford.  At the same time, recording
   details will provide evidence for prosecution efforts, providing the
   case moves in this direction.  Documenting an incident also will help
   you perform a final assessment of damage (something your management
   as well as law enforcement officers will want to know), and will
   provide the basis for a follow-up analysis in which you can engage in
   a valuable "lessons learned" exercise.

   During the initial stages of an incident, it is often infeasible to
   determine whether prosecution is viable, so you should document as if
   you are gathering evidence for a court case.  At a minimum, you
   should record:

      o All system events (audit records).
      o All actions you take (time tagged).
      o All phone conversations (including the person with whom
        you talked, the date and time, and the content of the

   The most straightforward way to maintain documentation is keeping a
   log book.  This allows you to go to a centralized, chronological
   source of information when you need it, instead of requiring you to
   page through individual sheets of paper.  Much of this information is
   potential evidence in a court of law.  Thus, when you initially
   suspect that an incident will result in prosecution or when an
   investigative agency becomes involved, you need to regularly (e.g.,
   every day) turn in photocopied, signed copies of your logbook (as
   well as media you use to record system events) to a document
   custodian who can store these copied pages in a secure place (e.g., a
   safe).  When you submit information for storage, you should in return
   receive a signed, dated receipt from the document custodian.  Failure
   to observe these procedures can result in invalidation of any
   evidence you obtain in a court of law.

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6.  Establishing Post-Incident Procedures

6.1  Overview

   In the wake of an incident, several actions should take place.  These
   actions can be summarized as follows:

      1. An inventory should be taken of the systems' assets,
         i.e., a careful examination should determine how the
         system was affected by the incident,

      2. The lessons learned as a result of the incident
         should be included in revised security plan to
         prevent the incident from re-occurring,

      3. A new risk analysis should be developed in light of the

      4. An investigation and prosecution of the individuals
         who caused the incident should commence, if it is
         deemed desirable.

   All four steps should provide feedback to the site security policy
   committee, leading to prompt re-evaluation and amendment of the
   current policy.

6.2  Removing Vulnerabilities

   Removing all vulnerabilities once an incident has occurred is
   difficult.  The key to removing vulnerabilities is knowledge and
   understanding of the breach.  In some cases, it is prudent to remove
   all access or functionality as soon as possible, and then restore
   normal operation in limited stages.  Bear in mind that removing all
   access while an incident is in progress will obviously notify all
   users, including the alleged problem users, that the administrators
   are aware of a problem; this may have a deleterious effect on an
   investigation.  However, allowing an incident to continue may also
   open the likelihood of greater damage, loss, aggravation, or
   liability (civil or criminal).

   If it is determined that the breach occurred due to a flaw in the
   systems' hardware or software, the vendor (or supplier) and the CERT
   should be notified as soon as possible.  Including relevant telephone
   numbers (also electronic mail addresses and fax numbers) in the site
   security policy is strongly recommended.  To aid prompt
   acknowledgment and understanding of the problem, the flaw should be
   described in as much detail as possible, including details about how
   to exploit the flaw.

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   As soon as the breach has occurred, the entire system and all its
   components should be considered suspect.  System software is the most
   probable target.  Preparation is key to recovering from a possibly
   tainted system.  This includes checksumming all tapes from the vendor
   using a checksum algorithm which (hopefully) is resistant to
   tampering [10].  (See sections,  Assuming original
   vendor distribution tapes are available, an analysis of all system
   files should commence, and any irregularities should be noted and
   referred to all parties involved in handling the incident.  It can be
   very difficult, in some cases, to decide which backup tapes to
   recover from; consider that the incident may have continued for
   months or years before discovery, and that the suspect may be an
   employee of the site, or otherwise have intimate knowledge or access
   to the systems.  In all cases, the pre-incident preparation will
   determine what recovery is possible.  At worst-case, restoration from
   the original manufactures' media and a re-installation of the systems
   will be the most prudent solution.

   Review the lessons learned from the incident and always update the
   policy and procedures to reflect changes necessitated by the

   6.2.1  Assessing Damage

      Before cleanup can begin, the actual system damage must be
      discerned.  This can be quite time consuming, but should lead into
      some of the insight as to the nature of the incident, and aid
      investigation and prosecution.  It is best to compare previous
      backups or original tapes when possible; advance preparation is
      the key.  If the system supports centralized logging (most do), go
      back over the logs and look for abnormalities.  If process
      accounting and connect time accounting is enabled, look for
      patterns of system usage.  To a lesser extent, disk usage may shed
      light on the incident.  Accounting can provide much helpful
      information in an analysis of an incident and subsequent

   6.2.2  Cleanup

      Once the damage has been assessed, it is necessary to develop a
      plan for system cleanup.  In general, bringing up services in the
      order of demand to allow a minimum of user inconvenience is the
      best practice.  Understand that the proper recovery procedures for
      the system are extremely important and should be specific to the

      It may be necessary to go back to the original distributed tapes
      and recustomize the system.  To facilitate this worst case

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      scenario, a record of the original systems setup and each
      customization change should be kept current with each change to
      the system.

   6.2.3  Follow up

      Once you believe that a system has been restored to a "safe"
      state, it is still possible that holes and even traps could be
      lurking in the system.  In the follow-up stage, the system should
      be monitored for items that may have been missed during the
      cleanup stage.  It would be prudent to utilize some of the tools
      mentioned in section (e.g., COPS) as a start.  Remember,
      these tools don't replace continual system monitoring and good
      systems administration procedures.

   6.2.4  Keep a Security Log

      As discussed in section 5.6, a security log can be most valuable
      during this phase of removing vulnerabilities.  There are two
      considerations here; the first is to keep logs of the procedures
      that have been used to make the system secure again.  This should
      include command procedures (e.g., shell scripts) that can be run
      on a periodic basis to recheck the security.  Second, keep logs of
      important system events.  These can be referenced when trying to
      determine the extent of the damage of a given incident.

6.3  Capturing Lessons Learned

   6.3.1  Understand the Lesson

      After an incident, it is prudent to write a report describing the
      incident, method of discovery, correction procedure, monitoring
      procedure, and a summary of lesson learned.  This will aid in the
      clear understanding of the problem.  Remember, it is difficult to
      learn from an incident if you don't understand the source.

   6.3.2  Resources  Other Security Devices, Methods

         Security is a dynamic, not static process.  Sites are dependent
         on the nature of security available at each site, and the array
         of devices and methods that will help promote security.
         Keeping up with the security area of the computer industry and
         their methods will assure a security manager of taking
         advantage of the latest technology.

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RFC 1244                 Site Security Handbook                July 1991  Repository of Books, Lists, Information Sources

         Keep an on site collection of books, lists, information
         sources, etc., as guides and references for securing the
         system.  Keep this collection up to date.  Remember, as systems
         change, so do security methods and problems.  Form a Subgroup

         Form a subgroup of system administration personnel that will be
         the core security staff.  This will allow discussions of
         security problems and multiple views of the site's security
         issues.  This subgroup can also act to develop the site
         security policy and make suggested changes as necessary to
         ensure site security.

6.4  Upgrading Policies and Procedures

   6.4.1  Establish Mechanisms for Updating Policies, Procedures,
          and Tools

      If an incident is based on poor policy, and unless the policy is
      changed, then one is doomed to repeat the past.  Once a site has
      recovered from and incident, site policy and procedures should be
      reviewed to encompass changes to prevent similar incidents.  Even
      without an incident, it would be prudent to review policies and
      procedures on a regular basis.  Reviews are imperative due to
      today's changing computing environments.

   6.4.2  Problem Reporting Procedures

      A problem reporting procedure should be implemented to describe,
      in detail, the incident and the solutions to the incident.  Each
      incident should be reviewed by the site security subgroup to allow
      understanding of the incident with possible suggestions to the
      site policy and procedures.

7.  References

   [1] Quarterman, J., "The Matrix: Computer Networks and Conferencing
       Systems Worldwide", Pg. 278, Digital Press, Bedford, MA, 1990.

   [2] Brand, R., "Coping with the Threat of Computer Security
       Incidents: A Primer from Prevention through Recovery", R. Brand,
       available on-line from:, 8 June

   [3] Fites, M., Kratz, P. and A. Brebner, "Control and Security of

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       Computer Information Systems", Computer Science Press, 1989.

   [4] Johnson, D., and J. Podesta, "Formulating a Company Policy on
       Access to and Use and Disclosure of Electronic Mail on Company
       Computer Systems", Available from: The Electronic Mail
       Association (EMA) 1555 Wilson Blvd, Suite 555, Arlington VA
       22209, (703) 522-7111, 22 October 1990.

   [5] Curry, D., "Improving the Security of Your UNIX System", SRI
       International Report ITSTD-721-FR-90-21, April 1990.

   [6] Cheswick, B., "The Design of a Secure Internet Gateway",
       Proceedings of the Summer Usenix Conference, Anaheim, CA, June

   [7] Linn, J., "Privacy Enhancement for Internet Electronic Mail: Part
       I -- Message Encipherment and Authentication Procedures", RFC
       1113, IAB Privacy Task Force, August 1989.

   [8] Kent, S., and J. Linn, "Privacy Enhancement for Internet
       Electronic Mail: Part II -- Certificate-Based Key Management",
       RFC 1114, IAB Privacy Task Force, August 1989.

   [9] Linn, J., "Privacy Enhancement for Internet Electronic Mail: Part
       III -- Algorithms, Modes, and Identifiers", RFC 1115, IAB Privacy
       Task Force, August 1989.

  [10] Merkle, R., "A Fast Software One Way Hash Function", Journal of
       Cryptology, Vol. 3, No. 1.

  [11] Postel, J., "Internet Protocol - DARPA Internet Program Protocol
       Specification", RFC 791, DARPA, September 1981.

  [12] Postel, J., "Transmission Control Protocol - DARPA Internet
       Program Protocol Specification", RFC 793, DARPA, September 1981.

  [13] Postel, J., "User Datagram Protocol", RFC 768, USC/Information
       Sciences Institute, 28 August 1980.

  [14] Mogul, J., "Simple and Flexible Datagram Access Controls for
       UNIX-based Gateways", Digital Western Research Laboratory
       Research Report 89/4, March 1989.

  [15] Bellovin, S., and M. Merritt, "Limitations of the Kerberos
       Authentication System", Computer Communications Review, October

  [16] Pfleeger, C., "Security in Computing", Prentice-Hall, Englewood

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       Cliffs, N.J., 1989.

  [17] Parker, D., Swope, S., and B. Baker, "Ethical Conflicts:
       Information and Computer Science, Technology and Business", QED
       Information Sciences, Inc., Wellesley, MA.

  [18] Forester, T., and P. Morrison, "Computer Ethics: Tales and
       Ethical Dilemmas in Computing", MIT Press, Cambridge, MA, 1990.

  [19] Postel, J., and J. Reynolds, "Telnet Protocol Specification", RFC
       854, USC/Information Sciences Institute, May 1983.

  [20] Postel, J., and J. Reynolds, "File Transfer Protocol", RFC 959,
       USC/Information Sciences Institute, October 1985.

  [21] Postel, J., Editor, "IAB Official Protocol Standards", RFC 1200,
       IAB, April 1991.

  [22] Internet Activities Board, "Ethics and the Internet", RFC 1087,
       Internet Activities Board, January 1989.

  [23] Pethia, R., Crocker, S., and B. Fraser, "Policy Guidelines for
       the Secure Operation of the Internet", CERT, TIS, CERT, RFC in

  [24] Computer Emergency Response Team (CERT/CC), "Unauthorized
       Password Change Requests", CERT Advisory CA-91:03, April 1991.

  [25] Computer Emergency Response Team (CERT/CC), "TELNET Breakin
       Warning", CERT Advisory CA-89:03, August 1989.

  [26] CCITT, Recommendation X.509, "The Directory: Authentication
       Framework", Annex C.

  [27] Farmer, D., and E. Spafford, "The COPS Security Checker System",
       Proceedings of the Summer 1990 USENIX Conference, Anaheim, CA,
       Pgs. 165-170, June 1990.

8.  Annotated Bibliography

   The intent of this annotated bibliography is to offer a
   representative collection of resources of information that will help
   the user of this handbook.  It is meant provide a starting point for
   further research in the security area.  Included are references to
   other sources of information for those who wish to pursue issues of
   the computer security environment.

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8.1  Computer Law

           American Bar Association, Section of Science and
           Technology, "Guide to the Prosecution of Telecommunication
           Fraud by the Use of Computer Crime Statutes", American Bar
           Association, 1989.

           Bender, D., "Computer Law: Evidence and Procedure",
           M. Bender, New York, NY, 1978-present.

           Kept up to date with supplements.
           Years covering 1978-1984 focuses on: Computer law,
           evidence and procedures.  The years 1984 to the current
           focus on general computer law.  Bibliographical
           references and index included.

           Bloombecker, B., "Spectacular Computer Crimes", Dow Jones-
           Irwin, Homewood, IL. 1990.

           Commerce Clearing House, "Guide to Computer Law", (Topical
           Law Reports), Chicago, IL., 1989.

           Court cases and decisions rendered by federal and state
           courts throughout the United States on federal and state
           computer law.  Includes Case Table and Topical Index.

           Conly, C., "Organizing for Computer Crime Investigation and
           Prosecution", U.S. Dept. of Justice, Office of Justice
           Programs, Under Contract  Number OJP-86-C-002, National
           Institute of Justice, Washington, DC, July 1989.

           Fenwick, W., Chair, "Computer Litigation, 1985: Trial
           Tactics and Techniques", Litigation Course Handbook
           Series No. 280, Prepared for distribution at the
           Computer Litigation, 1985: Trial Tactics and
           Techniques Program, February-March 1985.

           Gemignani, M., "Viruses and Criminal Law", Communications
           of the ACM, Vol. 32, No. 6, Pgs. 669-671, June 1989.

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           Huband, F., and R. Shelton, Editors, "Protection of
           Computer Systems and Software: New Approaches for Combating
           Theft of Software and Unauthorized Intrusion", Papers
           presented at a workshop sponsored by the National Science
           Foundation, 1986.

           McEwen, J., "Dedicated Computer Crime Units", Report
           Contributors: D. Fester and H. Nugent, Prepared for the
           National Institute of Justice, U.S. Department of Justice,
           by Institute for Law and Justice, Inc., under contract number
           OJP-85-C-006, Washington, DC, 1989.

           Parker, D., "Computer Crime: Criminal Justice Resource
           Manual", U.S. Dept. of Justice, National Institute of Justice,
           Office of Justice Programs, Under Contract Number
           OJP-86-C-002, Washington, D.C., August 1989.

           Shaw, E., Jr., "Computer Fraud and Abuse Act of 1986,
           Congressional Record (3 June 1986), Washington, D.C.,
           3 June 1986.

           Trible, P., "The Computer Fraud and Abuse Act of 1986",
           U.S. Senate Committee on the Judiciary, 1986.

8.2  Computer Security

           Caelli, W., Editor, "Computer Security in the Age of
           Information", Proceedings of the Fifth IFIP International
           Conference on Computer Security, IFIP/Sec '88.

           Carroll, J., "Computer Security", 2nd Edition, Butterworth
           Publishers, Stoneham, MA, 1987.

           Cooper, J., "Computer and Communications Security:
           Strategies for the 1990s", McGraw-Hill, 1989.

           Brand, R., "Coping with the Threat of Computer Security
           Incidents: A Primer from Prevention through Recovery",

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           R. Brand, 8 June 1990.

           As computer security becomes a more important issue in
           modern society, it begins to warrant a systematic approach.
           The vast majority of the computer security problems and the
           costs associated with them can be prevented with simple
           inexpensive measures.  The most important and cost
           effective of these measures are available in the prevention
           and planning phases.  These methods are presented in this
           paper, followed by a simplified guide to incident
           handling and recovery.  Available on-line from:

           Cheswick, B., "The Design of a Secure Internet Gateway",
           Proceedings of the Summer Usenix Conference, Anaheim, CA,
           June 1990.

           Brief abstract (slight paraphrase from the original
           abstract): AT&T maintains a large internal Internet that
           needs to be protected from outside attacks, while
           providing useful services between the two.
           This paper describes AT&T's Internet gateway.  This
           gateway passes mail and many of the common Internet
           services between AT&T internal machines and the Internet.
           This is accomplished without IP connectivity using a pair
           of machines: a trusted internal machine and an untrusted
           external gateway.  These are connected by a private link.
           The internal machine provides a few carefully-guarded
           services to the external gateway.  This configuration
           helps protect the internal internet even if the external
           machine is fully compromised.

           This is a very useful and interesting design.  Most
           firewall gateway systems rely on a system that, if
           compromised, could allow access to the machines behind
           the firewall.  Also, most firewall systems require users
           who want access to Internet services to have accounts on
           the firewall machine.  AT&T's design allows AT&T internal
           internet users access to the standard services of TELNET and
           FTP from their own workstations without accounts on
           the firewall machine.  A very useful paper that shows
           how to maintain some of the benefits of Internet
           connectivity while still maintaining strong

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           Curry, D., "Improving the Security of Your UNIX System",
           SRI International Report ITSTD-721-FR-90-21, April 1990.

           This paper describes measures that you, as a system
           administrator can take to make your UNIX system(s) more
           secure.  Oriented primarily at SunOS 4.x, most of the
           information covered applies equally well to any Berkeley
           UNIX system with or without NFS and/or Yellow Pages (NIS).
           Some of the information can also be applied to System V,
           although this is not a primary focus of the paper.  A very
           useful reference, this is also available on the Internet in
           various locations, including the directory

           Fites, M., Kratz, P. and A. Brebner, "Control and
           Security of Computer Information Systems", Computer Science
           Press, 1989.

           This book serves as a good guide to the issues encountered
           in forming computer security policies and procedures.  The
           book is designed as a textbook for an introductory course
           in information systems security.

           The book is divided into five sections: Risk Management (I),
           Safeguards: security and control measures, organizational
           and administrative (II), Safeguards: Security and Control
           Measures, Technical (III), Legal Environment and
           Professionalism (IV), and CICA Computer Control Guidelines

           The book is particularly notable for its straight-forward
           approach to security, emphasizing that common sense is the
           first consideration in designing a security program.  The
           authors note that there is a tendency to look to more
           technical solutions to security problems while overlooking
           organizational controls which are often cheaper and much
           more effective.  298 pages, including references and index.

           Garfinkel, S, and E. Spafford, "Practical Unix Security",
           O'Reilly & Associates, ISBN 0-937175-72-2, May 1991.

           Approx 450 pages, $29.95.  Orders: 1-800-338-6887
           (US & Canada), 1-707-829-0515 (Europe), email:

           This is one of the most useful books available on Unix

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           security.  The first part of the book covers standard Unix
           and Unix security basics, with particular emphasis on
           passwords.  The second section covers enforcing security on
           the system.  Of particular interest to the Internet user are
           the sections on network security, which address many
           of the common security problems that afflict Internet Unix
           users.  Four chapters deal with handling security incidents,
           and the book concludes with discussions of encryption,
           physical security, and useful checklists and lists of
           resources.  The book lives up to its name; it is filled with
           specific references to possible security holes, files to
           check, and things to do to improve security.  This
           book is an excellent complement to this handbook.

           Greenia, M., "Computer Security Information Sourcebook",
           Lexikon Services, Sacramento, CA, 1989.

           A manager's guide to computer security.  Contains a
           sourcebook of key reference materials including
           access control and computer crimes bibliographies.

           Hoffman, L., "Rogue Programs: Viruses, Worms, and
           Trojan Horses", Van Nostrand Reinhold, NY, 1990.
           (384 pages, includes bibliographical references and index.)

           Johnson, D., and J. Podesta, "Formulating A Company Policy
           on Access to and Use and Disclosure of Electronic Mail on
           Company Computer Systems".

           A white paper prepared for the EMA, written by two experts
           in privacy law.  Gives background on the issues, and presents
           some policy options.

           Available from: The Electronic Mail Association (EMA)
           1555 Wilson Blvd, Suite 555, Arlington, VA, 22209.
           (703) 522-7111.

           Kent, Stephen, "E-Mail Privacy for the Internet: New Software
           and Strict Registration Procedures will be Implemented this
           Year", Business Communications Review, Vol. 20, No. 1,
           Pg. 55, 1 January 1990.

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           Lu, W., and M. Sundareshan, "Secure Communication in
           Internet Environments: A Hierachical Key Management Scheme
           for End-to-End Encryption", IEEE Transactions on
           Communications, Vol. 37, No. 10, Pg. 1014, 1 October 1989.

           Lu, W., and M. Sundareshan, "A Model for Multilevel Security
           in Computer Networks", IEEE Transactions on Software
           Engineering, Vol. 16, No. 6, Page 647, 1 June 1990.

           National Security Agency, "Information Systems Security
           Products and Services Catalog", NSA, Quarterly Publication.

           NSA's catalogue contains chapter on: Endorsed Cryptographic
           Products List; NSA Endorsed Data Encryption Standard (DES)
           Products List; Protected Services List; Evaluated Products
           List; Preferred Products List; and Endorsed Tools List.

           The catalogue is available from the Superintendent of
           Documents, U.S. Government Printing Office, Washington,
           D.C.  One may place telephone orders by calling:
           (202) 783-3238.

           United States Congress, Office of Technology Assessment,
           "Defending Secrets, Sharing Data: New Locks and Keys for
           Electronic Information", OTA-CIT-310, October 1987.

           This report, prepared for congressional committee considering
           Federal policy on the protection of electronic information, is
           interesting because of the issues it raises regarding the
           impact of technology used to protect information.  It also
           serves as a reasonable introduction to the various encryption
           and information protection mechanisms.  185 pages.  Available
           from the U.S. Government Printing Office.

           Palmer, I., and G. Potter, "Computer Security Risk
           Management", Van Nostrand Reinhold, NY, 1989.

           Pfleeger, C., "Security in Computing", Prentice-Hall,
           Englewood Cliffs, NJ, 1989.

           A general textbook in computer security, this book provides an
           excellent and very readable introduction to classic computer

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           security problems and solutions, with a particular emphasis on
           encryption.  The encryption coverage serves as a good
           introduction to the subject.  Other topics covered include
           building secure programs and systems, security of database,
           personal computer security, network and communications
           security, physical security, risk analysis and security
           planning, and legal and ethical issues.  538 pages including
           index and bibliography.

           Shirey, R., "Defense Data Network Security Architecture",
           Computer Communication Review, Vol. 20, No. 2, Page 66,
           1 April 1990.

           Spafford, E., Heaphy, K., and D. Ferbrache, "Computer
           Viruses: Dealing with Electronic Vandalism and Programmed
           Threats", ADAPSO, 1989. (109 pages.)

           This is a good general reference on computer viruses and
           related concerns.  In addition to describing viruses in
           some detail, it also covers more general security issues,
           legal recourse in case of security problems, and includes
           lists of laws, journals focused on computers security,
           and other security-related resources.

           Available from: ADAPSO, 1300 N. 17th St, Suite 300,
           Arlington VA 22209.  (703) 522-5055.

           Stoll, C., "Stalking the Wily Hacker", Communications
           of the ACM, Vol. 31, No. 5, Pgs. 484-497, ACM,
           New York, NY, May 1988.

           This article describes some of the technical means used
           to trace the intruder that was later chronicled in
           "Cuckoo's Egg" (see below).

           Stoll, C., "The Cuckoo's Egg", ISBN 00385-24946-2,
           Doubleday, 1989.

           Clifford Stoll, an astronomer turned UNIX System
           Administrator, recounts an exciting, true story of how he
           tracked a computer intruder through the maze of American
           military and research networks.  This book is easy to
           understand and can serve as an interesting introduction to
           the world of networking.  Jon Postel says in a book review,

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           "[this book] ... is absolutely essential reading for anyone
           that uses or operates any computer connected to the Internet
           or any other computer network."

           Vallabhaneni, S., "Auditing Computer Security: A Manual with
           Case Studies", Wiley, New York, NY, 1989.

8.3  Ethics

           Computer Professionals for Social Responsibility, "CPSR
           Statement on the Computer Virus", CPSR, Communications of the
           ACM, Vol. 32, No. 6, Pg. 699, June 1989.

           This memo is a statement on the Internet Computer Virus
           by the Computer Professionals for Social Responsibility

           Denning, Peter J., Editor, "Computers Under Attack:
           Intruders, Worms, and Viruses",  ACM Press, 1990.

           A collection of 40 pieces divided into six sections: the
           emergence of worldwide computer networks, electronic breakins,
           worms, viruses, counterculture (articles examining the world
           of the "hacker"), and finally a section discussing social,
           legal, and ethical considerations.

           A thoughtful collection that addresses the phenomenon of
           attacks on computers.  This includes a number of previously
           published articles and some new ones.  The previously
           published ones are well chosen, and include some references
           that might be otherwise hard to obtain.  This book is a key
           reference to computer security threats that have generated
           much of the concern over computer security in recent years.

           Ermann, D., Williams, M., and C. Gutierrez, Editors,
           "Computers, Ethics, and Society", Oxford University Press,
           NY, 1990.  (376 pages, includes bibliographical references).

           Forester, T., and P. Morrison, "Computer Ethics: Tales and
           Ethical Dilemmas in Computing", MIT Press, Cambridge, MA,
           1990.  (192 pages including index.)

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           From the preface: "The aim of this book is two-fold: (1) to
           describe some of the problems created by society by computers,
           and (2) to show how these problems present ethical dilemmas
           for computers professionals and computer users.

           The problems created by computers arise, in turn, from two
           main sources: from hardware and software malfunctions and
           from misuse by human beings.  We argue that computer systems
           by their very nature are insecure, unreliable, and
           unpredictable -- and that society has yet to come to terms
           with the consequences.  We also seek to show how society
           has become newly vulnerable to human misuse of computers in
           the form of computer crime, software theft, hacking, the
           creation of viruses, invasions of privacy, and so on."

           The eight chapters include "Computer Crime", "Software
           Theft", "Hacking and Viruses", "Unreliable Computers",
           "The Invasion of Privacy", "AI and Expert Systems",
           and "Computerizing the Workplace."  Includes extensive
           notes on sources and an index.

           Gould, C., Editor, "The Information Web: Ethical and Social
           Implications of Computer Networking", Westview Press,
           Boulder, CO, 1989.

           Internet Activities Board, "Ethics and the Internet",
           RFC 1087, IAB, January 1989.  Also appears in the
           Communications of the ACM, Vol. 32, No. 6, Pg. 710,
           June 1989.

           This memo is a statement of policy by the Internet
           Activities Board (IAB) concerning the proper use of
           the resources of the Internet.  Available on-line on
           host, directory rfc, filename rfc1087.txt.
           Also available on host, directory RFC,
           filename RFC1087.TXT-1.

           Martin, M., and R. Schinzinger, "Ethics in Engineering",
           McGraw Hill, 2nd Edition, 1989.

           Massachusetts Institute of Technology, "Teaching Students
           About Responsible Use of Computers", MIT, 1985-1986.  Also
           reprinted in the Communications of the ACM, Vol. 32, No. 6,
           Pg. 704, Athena Project, MIT, June 1989.

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           This memo is a statement of policy by the Massachusetts
           Institute of Technology (MIT) on the responsible use
           of computers.

           National Institute of Standards and Technology, "Computer
           Viruses and Related Threats: A Management Guide", NIST
           Special Publication 500-166, August 1989.

           National Science Foundation, "NSF Poses Code of Networking
           Ethics", Communications of the ACM, Vol. 32, No. 6, Pg. 688,
           June 1989.  Also appears in the minutes of the regular
           meeting of the Division Advisory Panel for Networking and
           Communications Research and Infrastructure, Dave Farber,
           Chair, November 29-30, 1988.

           This memo is a statement of policy by the National Science
           Foundation (NSF) concerning the ethical use of the Internet.

           Parker, D., Swope, S., and B. Baker, "Ethical Conflicts:
           Information and Computer Science, Technology and Business",
           QED Information Sciences, Inc., Wellesley, MA. (245 pages).

   Additional publications on Ethics:

   The University of New Mexico (UNM)

      The UNM has a collection of ethics documents.  Included are
      legislation from several states and policies from many

         Access is via FTP, IP address  Look in the
         directory /ethics.

8.4  The Internet Worm

           Brock, J., "November 1988 Internet Computer Virus and the
           Vulnerability of National Telecommunications Networks to
           Computer Viruses", GAO/T-IMTEC-89-10, Washington, DC,
           20 July 1989.

           Testimonial statement of Jack L. Brock, Director, U. S.
           Government Information before the Subcommittee on
           Telecommunications and Finance, Committee on Energy and

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           Commerce, House of Representatives.

           Eichin, M., and J. Rochlis, "With Microscope and Tweezers:
           An Analysis of the Internet Virus of November 1988",
           Massachusetts Institute of Technology, February 1989.

           Provides a detailed dissection of the worm program.  The
           paper discusses the major points of the worm program then
           reviews strategies, chronology, lessons and open issues,
           Acknowledgments; also included are a detailed appendix
           on the worm program subroutine by subroutine, an
           appendix on the cast of characters, and a reference section.

           Eisenberg, T., D. Gries, J. Hartmanis, D. Holcomb,
           M. Lynn, and T. Santoro, "The Computer Worm", Cornell
           University, 6 February 1989.

           A Cornell University Report presented to the Provost of the
           University on 6 February 1989 on the Internet Worm.

           U.S. General Accounting Office, "Computer Security - Virus
           Highlights Need for Improved Internet Management", United
           States General Accounting Office, Washington, DC, 1989.

           This 36 page report (GAO/IMTEC-89-57), by the U.S.
           Government Accounting Office, describes the Internet worm
           and its effects.  It gives a good overview of the various
           U.S. agencies involved in the Internet today and their
           concerns vis-a-vis computer security and networking.

           Available on-line on host, directory
           pub, filename GAO_RPT; and on, directory nsfnet,
           filename GAO_RPT.TXT.

           The Helminthiasis of the Internet, RFC 1135,
           USC/Information Sciences Institute, Marina del Rey,
           CA, December 1989.

           This report looks back at the helminthiasis (infestation
           with, or disease caused by parasitic worms) of the
           Internet that was unleashed the evening of 2 November 1988.
           This document provides a glimpse at the infection,its
           festering, and cure.  The impact of the worm on the Internet
           community, ethics statements, the role of the news media,

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           crime in the computer world, and future prevention is
           discussed.  A documentation review presents four publications
           that describe in detail this particular parasitic computer
           program.  Reference and bibliography sections are also
           included.  Available on-line on host
           directory rfc, filename rfc1135.txt.  Also available on
           host, directory RFC, filename RFC1135.TXT-1.

           Seeley, D., "A Tour of the Worm", Proceedings of 1989
           Winter USENIX Conference, Usenix Association, San Diego, CA,
           February 1989.

           Details are presented as a "walk thru" of this particular
           worm program.  The paper opened with an abstract,
           introduction, detailed chronology of events upon the
           discovery of the worm, an overview, the internals of the
           worm, personal opinions, and conclusion.

           Spafford, E., "The Internet Worm Program: An
           Analysis", Computer Communication Review, Vol. 19,
           No. 1, ACM SIGCOM, January 1989.  Also issued as Purdue
           CS Technical Report CSD-TR-823, 28 November 1988.

           Describes the infection of the Internet as a worm
           program that exploited flaws in utility programs in
           UNIX based systems.  The report gives a detailed
           description of the components of the worm program:
           data and functions.  Spafford focuses his study on two
           completely independent reverse-compilations of the
           worm and a version disassembled to VAX assembly language.

           Spafford, G., "An Analysis of the Internet Worm",
           Proceedings of the European Software Engineering
           Conference 1989, Warwick England, September 1989.
           Proceedings published by Springer-Verlag as: Lecture
           Notes in Computer Science #387.  Also issued
           as Purdue Technical Report #CSD-TR-933.

8.5  National Computer Security Center (NCSC)

   All NCSC publications, approved for public release, are available
   from the NCSC Superintendent of Documents.

           NCSC = National Computer Security Center

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           9800 Savage Road
           Ft Meade, MD 20755-6000

           CSC = Computer Security Center:
           an older name for the NCSC

           NTISS = National Telecommunications and
           Information Systems Security
           NTISS Committee, National Security Agency
           Ft Meade, MD 20755-6000

           Department of Defense, "Password Management Guideline",
           CSC-STD-002-85, 12 April 1985, 31 pages.

           The security provided by a password system depends on
           the passwords being kept secret at all times.  Thus, a
           password is vulnerable to compromise whenever it is used,
           stored, or even known.  In a password-based authentication
           mechanism implemented on an ADP system, passwords are
           vulnerable to compromise due to five essential aspects
           of the password system: 1) a password must be initially
           assigned to a user when enrolled on the ADP system;
           2) a user's password must be changed periodically;
           3) the ADP system must maintain a 'password
           database'; 4) users must remember their passwords; and
           5) users must enter their passwords into the ADP system at
           authentication time.  This guideline prescribes steps to be
           taken to minimize the vulnerability of passwords in each of
           these circumstances.

           NCSC, "A Guide to Understanding AUDIT in Trusted Systems",
           NCSC-TG-001, Version-2, 1 June 1988, 25 pages.

           Audit trails are used to detect and deter penetration of
           a computer system and to reveal usage that identifies
           misuse.  At the discretion of the auditor, audit trails
           may be limited to specific events or may encompass all of
           the activities on a system.  Although not required by
           the criteria, it should be possible for the target of the
           audit mechanism to be either a subject or an object.  That
           is to say, the audit mechanism should be capable of
           monitoring every time John accessed the system as well as
           every time the nuclear reactor file was accessed; and
           likewise every time John accessed the nuclear reactor

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           NCSC, "A Guide to Understanding DISCRETIONARY ACCESS CONTROL
           in Trusted Systems", NCSC-TG-003, Version-1, 30 September
           1987, 29 pages.

           Discretionary control is the most common type of access
           control mechanism implemented in computer systems today.
           The basis of this kind of security is that an individual
           user, or program operating on the user's behalf, is
           allowed to specify explicitly the types of access other
           users (or programs executing on their behalf) may have to
           information under the user's control.  [...]  Discretionary
           controls are not a replacement for mandatory controls.  In
           any environment in which information is protected,
           discretionary security provides for a finer granularity of
           control within the overall constraints of the mandatory

           NCSC, "A Guide to Understanding CONFIGURATION MANAGEMENT
           in Trusted Systems", NCSC-TG-006, Version-1, 28 March 1988,
           31 pages.

           Configuration management consists of four separate tasks:
           identification, control, status accounting, and auditing.
           For every change that is made to an automated data
           processing (ADP) system, the design and requirements of the
           changed version of the system should be identified.  The
           control task of configuration management is performed
           by subjecting every change to documentation, hardware, and
           software/firmware to review and approval by an authorized
           authority.  Configuration status accounting is responsible
           for recording and reporting on the configuration of the
           product throughout the change.  Finally, though the process
           of a configuration audit, the completed change can be
           verified to be functionally correct, and for trusted
           systems, consistent with the security policy of the system.

           NTISS, "Advisory Memorandum on Office Automation Security
           Guideline", NTISSAM CONPUSEC/1-87, 16 January 1987,
           58 pages.

           This document provides guidance to users, managers, security
           officers, and procurement officers of Office Automation
           Systems.  Areas addressed include: physical security,
           personnel security, procedural security, hardware/software
           security, emanations security (TEMPEST), and communications

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           security for stand-alone OA Systems, OA Systems
           used as terminals connected to mainframe computer systems,
           and OA Systems used as hosts in a Local Area Network (LAN).
           Differentiation is made between those Office Automation
           Systems equipped with removable storage media only (e.g.,
           floppy disks, cassette tapes, removable hard disks) and
           those Office Automation Systems equipped with fixed media
           (e.g., Winchester disks).

Additional NCSC Publications:

           National Computer Security Center, "Glossary of Computer
           Security Terms", NCSC-TG-004, NCSC, 21 October 1988.

           National Computer Security Center, "Trusted
           Computer System Evaluation Criteria", DoD 5200.28-STD,
           CSC-STD-001-83, NCSC, December 1985.

           National Computer Security Center, "Guidance for
           Applying the Department of Defense Trusted Computer System
           Evaluation Criteria in Specific Environments",
           CSC-STD-003-85, NCSC, 25 June 1985.

           National Computer Security Center, "Technical Rationale
           Behind CSC-STD-003-85: Computer Security Requirements",
           CSC-STD-004-85, NCSC, 25 June 85.

           National Computer Security Center, "Magnetic Remanence
           Security Guideline", CSC-STD-005-85, NCSC, 15 November 1985.

           This guideline is tagged as a "For Official Use Only"
           exemption under Section 6, Public Law 86-36 (50 U.S. Code
           402).  Distribution authorized of U.S. Government agencies
           and their contractors to protect unclassified technical,
           operational, or administrative data relating to operations
           of the National Security Agency.

           National Computer Security Center, "Guidelines for Formal
           Verification Systems", Shipping list no.: 89-660-P, The
           Center, Fort George G. Meade, MD, 1 April 1990.

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           National Computer Security Center, "Glossary of Computer
           Security Terms", Shipping list no.: 89-254-P, The Center,
           Fort George G. Meade, MD, 21 October 1988.

           National Computer Security Center, "Trusted UNIX Working
           Group (TRUSIX) rationale for selecting access control
           list features for the UNIX system", Shipping list no.:
           90-076-P, The Center, Fort George G. Meade, MD, 1990.

           National Computer Security Center, "Trusted Network
           Interpretation", NCSC-TG-005, NCSC, 31 July 1987.

           Tinto, M., "Computer Viruses: Prevention, Detection, and
           Treatment", National Computer Security Center C1
           Technical Report C1-001-89, June 1989.

           National Computer Security Conference, "12th National
           Computer Security Conference: Baltimore Convention Center,
           Baltimore, MD, 10-13 October, 1989: Information Systems
           Security, Solutions for Today - Concepts for Tomorrow",
           National Institute of Standards and National Computer
           Security Center, 1989.

8.6  Security Checklists

           Aucoin, R., "Computer Viruses: Checklist for Recovery",
           Computers in  Libraries, Vol. 9, No. 2, Pg. 4,
           1 February 1989.

           Wood, C., Banks, W., Guarro, S., Garcia, A., Hampel, V.,
           and H. Sartorio, "Computer Security:  A Comprehensive Controls
           Checklist", John Wiley and Sons, Interscience Publication,

8.7  Additional Publications

   Defense Data Network's Network Information Center (DDN NIC)

      The DDN NIC maintains DDN Security bulletins and DDN Management

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      bulletins online on the machine: NIC.DDN.MIL.  They are available
      via anonymous FTP.  The DDN Security bulletins are in the
      directory: SCC, and the DDN Management bulletins are in the
      directory: DDN-NEWS.

      For additional information, you may send a message to:
      NIC@NIC.DDN.MIL, or call the DDN NIC at: 1-800-235-3155.

           Defense Data Network, "BSD 4.2 and 4.3 Software Problem
           Resolution", DDN MGT Bulletin #43, DDN Network Information
           Center, 3 November 1988.

           A Defense Data Network Management Bulletin announcement
           on the 4.2bsd and 4.3bsd software fixes to the Internet

           DCA DDN Defense Communications System, "DDN Security
           Bulletin 03", DDN Security Coordination Center,
           17 October 1989.

   IEEE Proceedings

           "Proceedings of the IEEE Symposium on Security
           and Privacy", published annually.

      IEEE Proceedings are available from:

              Computer Society of the IEEE
              P.O. Box 80452
              Worldway Postal Center
              Los Angeles, CA  90080

   Other Publications:

      Computer Law and Tax Report
      Computers and Security
      Security Management Magazine
      Journal of Information Systems Management
      Data Processing & Communications Security
      SIG Security, Audit & Control Review

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9.  Acknowledgments

   Thanks to the SSPHWG's illustrious "Outline Squad", who assembled at
   USC/Information Sciences Institute on 12-June-90: Ray Bates (ISI),
   Frank Byrum (DEC), Michael A. Contino (PSU), Dave Dalva (Trusted
   Information Systems, Inc.), Jim Duncan (Penn State Math Department),
   Bruce Hamilton (Xerox), Sean Kirkpatrick (Unisys), Tom Longstaff
   (CIAC/LLNL), Fred Ostapik (SRI/NIC), Keith Pilotti (SAIC), and Bjorn
   Satdeva (/sys/admin, inc.).

   Many thanks to Rich Pethia and the Computer Emergency Response Team
   (CERT); much of the work by Paul Holbrook was done while he was
   working for CERT.  Rich also provided a very thorough review of this
   document.  Thanks also to Jon Postel and USC/Information Sciences
   Institute for contributing facilities and moral support to this

   Last, but NOT least, we would like to thank members of the SSPHWG and
   Friends for their additional contributions: Vint Cerf (CNRI),
   Dave Grisham (UNM), Nancy Lee Kirkpatrick (Typist Extraordinaire),
   Chris McDonald (WSMR), H. Craig McKee (Mitre), Gene Spafford (Purdue),
   and Aileen Yuan (Mitre).

10.  Security Considerations

   If security considerations had not been so widely ignored in the
   Internet, this memo would not have been possible.

11.  Authors' Addresses

   J. Paul Holbrook
   CICNet, Inc.
   2901 Hubbard
   Ann Arbor, MI 48105

   Phone: (313) 998-7680

   Joyce K. Reynolds
   University of Southern California
   Information Sciences Institute
   4676 Admiralty Way
   Marina del Rey, CA 90292

   Phone: (213) 822-1511

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