Internet Engineering Task Force Dominique Brezinski INTERNET-DRAFT [...] Valid for six months Tom Killalea neart.org July 2000 Guidelines for Evidence Collection and Archiving Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright Notice Copyright (C) The Internet Society (2000). All Rights Reserved. Abstract The purpose of this document is to provide System Administrators with guidelines on the collection and archiving of evidence. Table of Contents 1 Introduction 1.1 Conventions Used in this Document 2 Guiding Principles during Evidence Collection 2.1 Order of Volatility Brezinski & Killalea [Page 1] Internet Draft Evidence Collection and Archiving 9 July 2000 2.2 Things to avoid 3 The Collection Procedure 3.1 Transparency 3.2 Collection Steps 4 The Archiving Procedure 4.1 Chain of Custody 4.2 The Archive 5 Tools you'll need 6 Security Considerations 7 Author's Address 8 Full Copyright Statement 1 Introduction The purpose of this document is to provide System Administrators with guidelines on the collection and archiving of evidence. It's not our intention to insist that all System Administrators rigidly follow these guidelines every time they have a security incident. Rather, we want to provide guidance on what they should do if they elect to collect and protect information relating to an intrusion. Such collection represents a considerable effort on the part of the System Administrator. Great progress has been made in recent years to speed up the re-installation of the Operating System and to facilitate the reversion of a system to a 'known' state, thus making the 'easy option' even more attractive. Meanwhile little has been done to provide easy ways of archiving evidence (the difficult option). Further, increasing disk and memory capacities and the more widespread use of stealth and cover-your-tracks tactics by attackers have exacerbated the problem. If evidence collection is done correctly, it is much more useful in apprehending the attacker, and stands a much greater chance of being admissible in the event of a prosecution. You should use these guidelines as a basis for formulating your site's evidence collection procedures, and should incorporate your site's procedures into your Incident Handling documentation. The guidelines in this document may not be appropriate under all jurisdictions. Once you've formulated your site's evidence collection procedures, you should have law enforcement for your Brezinski & Killalea [Page 2] Internet Draft Evidence Collection and Archiving 9 July 2000 jurisdiction confirm that they're adequate. 1.1 Conventions Used in this Document The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" in this document are to be interpreted as described in "Key words for use in RFCs to Indicate Requirement Levels" [RFC2119]. 2 Guiding Principles during Evidence Collection - Adhere to your site's Security Policy and engage the appropriate Incident Handling and Law Enforcement personnel. - Capture as accurate a picture of the system as possible. - Keep detailed notes. These should include dates and times. If possible generate an automatic transcript. (e.g., The 'script' program can be used, however the output file it generates should not be to media that is part of the evidence). - Be prepared to testify (perhaps years later) outlining all actions you took and at what times. Detailed notes will be vital. - Minimise changes to the data as you are collecting it. This is not limited to content changes; you should avoid updating file or directory access times. - Remove external avenues for change. - When confronted with a choice between collection and analysis you should do collection first and analysis later. - Though it hardly needs stating, your procedures should be implementable. If possible procedures should be automated for reasons of speed and accuracy. Be methodical. - Speed will often be critical so your team should break up and collect evidence from multiple systems (including network devices) in parallel. However on a single given system collection should be done step by step, strictly according to your collection procedure. - Proceed from the volatile to the less volatile (see the Order of Volatility below). Brezinski & Killalea [Page 3] Internet Draft Evidence Collection and Archiving 9 July 2000 - You should make a bit-level copy of the system's media. If you wish to do forensics analysis you should make a bit-level copy of your evidence copy for that purpose, as your analysis will almost certainly alter file access times. Avoid doing forensics on the evidence copy. 2.1 Order of Volatility When collecting evidence you should proceed from the volatile to the less volatile. Here is an example order of volatility for a typical system. - Registers, cache - routing table, arp cache, process table, kernel statistics - Memory - temporary file systems - Disk - physical configuration, network topology 2.2 Things to avoid It's all too easy to destroy evidence, however inadvertently. - Don't shutdown until you've completed evidence collection. Much evidence may be lost and the attacker may have altered the startup/shutdown scripts/services to destroy evidence. - Don't trust the programs on the system. Run your evidence gathering programs from your Forensics CD (see below) or similar read-only media. - Don't run programs that modify the access time of all files on the system (e.g., 'tar' or 'xcopy'). 3 The Collection Procedure Your collection procedures should be as detailed as possible. As is the case with your overall Incident Handling procedures, they should be unambiguous, and should minimise the amount of decision-making needed during the collection process. Brezinski & Killalea [Page 4] Internet Draft Evidence Collection and Archiving 9 July 2000 3.1 Transparency The methods used to collect evidence should be transparent. You should be prepared to disclose precisely the methods you used, and have those methods tested by independent experts. 3.2 Collection Steps - Where is the evidence ? List what systems were involved in the incident and from which evidence will be collected. - Establish what is likely to be relevant and admissable. When in doubt err on the side of collecting too much rather than not enough. - For each system, obtain the relevant order of volatility. - Remove external avenues for change. - Following the order of volatility, collect the evidence with tools as discussed in Section 5. - Question what else may be evidence as you work through the collection steps. - Document each step. Where feasible you should consider cryptographically signing the collected evidence, as this may make it easier to preserve a strong chain of evidence. In doing so you must not alter the evidence. 4 The Archiving Procedure Evidence must be strictly secured. In addition, the Chain of Custody needs to be clearly documented. 4.1 Chain of Custody You should be able to clearly describe how the evidence was found, how it was handled and everything that happened to it. The following need to be documented - Where, when and by whom was the evidence discovered. Brezinski & Killalea [Page 5] Internet Draft Evidence Collection and Archiving 9 July 2000 - Where, when and by whom was the evidence handled or examined. - Who had custody of the evidence, during what period. How was it stored. - When the evidence changed custody, when and how did the transfer occur (include shipping numbers, etc.). 4.2 Where and how to Archive If possible commonly used media (rather than some obscure storage media) should be used for archiving. Access to evidence should be extremely restricted, and should be clearly documented. It should be possible to detect unauthorised access. 5 Tools you'll need You should have the programs you need to do evidence collection and forensics on read-only media (e.g., CD). You should have prepared such a CD for each of the Operating Systems that you manage in advance of having to use it. When your systems are in production you might consider leaving a Forensics CD in the CD drive of each system, especially if your systems rarely need to use the CD drive after the installation process. Your forensics CD should include the following - a program for examining processes (e.g., 'ps'). - programs for examining system state (e.g., 'showrev', 'ifconfig', 'netstat', 'arp'). - a program for doing bit-to-bit copies (e.g., 'dd'). - programs for generating core images and for examining them (e.g, 'gcore', 'gdb'). - scripts to automate evidence collection (e.g., The Coroner's Toolkit [FAR1999]). The programs on the forensics CD should be statically linked, and should not require the use of any libraries other than those on the CD. Brezinski & Killalea [Page 6] Internet Draft Evidence Collection and Archiving 9 July 2000 You should be prepared to testify to the authenticity and reliability of the tools that you use. 6 References [FAR1999] Farmer, D., and W Venema, "Computer Forensics Analysis Class Handouts", http://www.fish.com/forensics/ [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [RFC2196] Fraser, B., "Site Security Handbook", RFC 2196, September 1997. [RFC2350] Brownlee, N., and E. Guttman, "Expectations for Computer Security Incident Response", RFC 2350, June 1998. 7 Acknowledgements We gratefully acknowledge the constructive comments received from Barbara Y. Fraser and Floyd Short. 6 Security Considerations This entire document discusses security issues. 7 Authors' Addresses Dominique Brezinski USA Tom Killalea P.O. Box 81226 Seattle, WA 98108-1226 USA Phone: +1 206 266-2196 E-Mail: tomk@neart.org 8 Full Copyright Statement Copyright (C) The Internet Society (2000). All Rights Reserved. Brezinski & Killalea [Page 7] Internet Draft Evidence Collection and Archiving 9 July 2000 This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implmentation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organisations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. 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