wdiff draft-ietf-ipsec-isakmp-02.txt draft-ietf-ipsec-isakmp-03.txt

IPSEC Working Group Douglas Maughan, Barbara Patrick, Mark Schertler
INTERNET-DRAFT National Security Agency
draft-ietf-ipsec-isakmp-02.txt,
draft-ietf-ipsec-isakmp-03.txt, .ps October 31, November 21, 1995

Internet Security Association and Key Management Protocol (ISAKMP)

Abstract

This memo describes a protocol utilizing security concepts
necessary for establishing Security Associations (SA) and crypto-
graphic keys in an Internet environment. A Security Association
protocol that negotiates, establishes, modifies and deletes
Security Associations and their attributes is required for an
evolving Internet, where there will be numerous security mecha-
nisms and several options for each security mechanism. The key
management protocol must be robust in order to handle public key
generation for the Internet community at large and private key
requirements for those private networks with that requirement.
The Internet Security Association and Key Management Protocol
(ISAKMP) defines the procedures for authenticating a communicat-
ing peer, creation and management of Security Associations, key
generation techniques, and threat mitigation (e.g. denial of
service and replay attacks). All of these are necessary to es-
tablish and maintain secure communications (via IP Security Ser-
vice or any other security protocol) in an Internet environment.

Status of this memo

This document is being submitted to the IETF Internet Protocol Security
(IPSEC) Working Group for consideration as a method for the establish-
ment and management of security associations and their appropriate secu-
rity attributes. Additionally, this document proposes a method for key
management to support IPSP and IPv6. Publication of this document does
not imply acceptance of the concepts discussed by the IPSEC Working Group.
Comments are solicited and should be addressed to the authors and/or the
working group mailing list at ipsec@ans.net.

This document is an Internet Draft. 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 not appropriate to use Internet Drafts as reference
material or to cite them other than as ``working draft'' or ``work in
progress.''

To learn the current status of any Internet-Draft, please check the ``1id-
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Distribution of this document is unlimited.

Contents

1 Introduction 4 5
1.1 Authentication . . . . . . . . . . . . . . . . . . . . . . . . . 4 6
1.1.1Certificate Authorities . . . . . . . . . . . . . . . . . . . 6
1.1.2Entity Naming . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1.3ISAKMP Requirements . . . . . . . . . . . . . . . . . . . . . 7
1.2 Security Associations and Management . . . . . . . . . . . . . . 5 8
1.2.1Security Associations and Registration . . . . . . . . . . . . 8
1.2.2ISAKMP Requirements . . . . . . . . . . . . . . . . . . . . . 8
1.3 Public Key Cryptography . . . . . . . . . . . . . . . . . . . . . 5 9
1.3.1Key Exchange Properties . . . . . . . . . . . . . . . . . . . 9
1.3.2ISAKMP Requirements . . . . . . . . . . . . . . . . . . . . . 11
1.4 Back Traffic ISAKMP Protection / Perfect Forward Secrecy . . . . . . . . 6

1.5 Anti-Clogging . . . . . . . . . . . . . . . . 11
1.4.1Anti-Clogging (Denial of Service) . . . . . . . . . . . . 6

1.5.1Anti-Clogging Token Creation . . 11
1.4.2Connection Hijacking . . . . . . . . . . . . . . . 7

1.6 . . . . . . 11
1.4.3Man-in-the-Middle Attacks . . . . . . . . . . . . . . . . . . 11
1.5 Multicast Communications . . . . . . . . . . . . . . . . . . . . 7 12

2 Description of the Protocol 8 12
2.1 ISAKMP Header Format . . . . . . . . . . . . . . . . . . . . . . 8 13
2.1.1General Message Processing . . . . . . . . . . . . . . . . . . 10 15
2.2 ISAKMP Packet Exchanges . . . . . . . . . . . . . . . . . . . . . 17
2.2.1Base Exchange . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2.2Identity Protection Exchange . . . . . . . . . . . . . . . . . 17
2.2.3Authentication Only Exchange . . . . . . . . . . . . . . . . . 18
2.3 ISAKMP Details . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2.1Security 19
2.3.1Security Association Attributes . . . . . . . . . . . . . . . 11

2.2.2Transport 19
2.3.2Transport Protocol . . . . . . . . . . . . . . . . . . . . . . 13

2.2.3RESERVED 21
2.3.3RESERVED Fields . . . . . . . . . . . . . . . . . . . . . . . 14

2.3 21
2.3.4Anti-Clogging Token (``Cookie'') Creation . . . . . . . . . . 21
2.3.5SA Flags Field . . . . . . . . . . . . . . . . . . . . . . . . 22
3 Security Association Establishment 22
3.1 Security Association Initialization . . . . . . . . . . . . . . . 14

2.3.1Security Association 22
3.1.1SA Initialization Procedures . . . . . . . . . . . . . 14

2.3.2Key and . . . . 24
3.2 Authentication Phase and Key Exchange . . . . . . . . . . . . . . . . . 25
3.2.1Authentication Payload Format . . . . . . . . . . . . . . . . 26
3.2.2Key Exchange Payload Format . . . . . . . . . . . . . . . . . 28
3.2.3Authentication and Key Exchange Procedures . . . . . . . . . . 16

2.3.3Security 29
3.3 Security Association Negotiation Phase . . . . . . . . . . . . 22

2.3.4Packet Exchanges . . . . 30
3.3.1SA Negotiation Procedures . . . . . . . . . . . . . . . . . . 31
3.4 SA Negotiation Conclusion . . . . . . 25

2.4 . . . . . . . . . . . . . . 34
3.4.1SA Negotiation Conclusion Procedures . . . . . . . . . . . . . 34

4 Security Association Modification 36
4.1 Modification Procedures . . . . . . . . . . . . . . . . 26

2.5 . . . . . 36
5 Security Association Deletion 36
5.1 Deletion Procedures . . . . . . . . . . . . . . . . . . . . 27

2.6 . . . 37

6 Notification Message 39
6.1 Notification Procedures . . . . . . . . . . . . . . . . . . . . . . 28

3 40

7 Conclusions 29 41

A Key Exchange Examples 30 ISAKMP Scenarios 43
A.1 Photuris KE Initial ISAKMP Daemon Scenerio . . . . . . . . . . . . . . . . . 43
A.2 Virtual Private Network Scenario . . . . . . . . . . . . 30

A.2 FORTEZZA Key Exchange Algorithm (KEA) . . . . 44
B Security Association Attributes 47

C Security Association Examples 51
C.1 ISAKMP SA Definition . . . . . . . . . . . . . . 30

B Security Association Attributes 32 . . . . . . . . 51
C.1.1ISAKMP SA Examples . . . . . . . . . . . . . . . . . . . . . . 52
C.2 ESP SA and AH SA Definitions . . . . . . . . . . . . . . . . . . 53
C.2.1ESP and AH SA Examples . . . . . . . . . . . . . . . . . . . . 54
C.2.2Fortezza SA Examples . . . . . . . . . . . . . . . . . . . . . 55

1 Introduction

This document describes an Internet Security Association and Key Manage-
ment Protocol (ISAKMP). ISAKMP combines the security concepts of authenti-
cation, authen-
tication, key management, and security associations to establish the desired re-
quired security for government, commercial, and private communications on
the In-
ternet. Internet. ISAKMP does extends the assertion in [DOW92] that authentica-
tion and key exchanges must be combined for better security to include se-
curity association exchanges. The security required for communications
depends on the individual network configurations and environments. Orga-
nizations are setting up Virtual Private Networks (VPN) that will require
one set of security functions for communications within the VPN and possi-
bly many different security functions for communications outside the VPN
to support geographically separate organizational components, customers,
suppliers, sub-contractors (with their own VPNs), government, and others.
Departments within large organizations may require a number of security
associations to separate and protect data (e.g. personnel data, company
proprietary data, medical) on internal networks and other security associ-
ations to communicate inter-department. Nomadic users wanting to ``phone
home'' represent another set of security requirements. These requirements
must be tempered with bandwidth challenges. Smaller groups of people may
meet their security requirements by setting up ``Webs of Trust''. ISAKMP
exchanges provide these assorted networking communities the ability to
present peers with the security functionality it supports in an authen-
ticated and protected manner for agreement upon a common interoperable se-
curity association.

Security associations must support different encryption algorithms, au-
thentication mechanisms, and key establishment algorithms for other secu-
rity protocols, as well as IP Security. Security associations must also
support host-oriented certificates for lower layer protocols and user-
oriented certificates for higher level protocols. Algorithm and mecha-
nism independence is required in applications such as e-mail, remote lo-
gin, and file transfer, as well as in session oriented protocols, routing
protocols, and link layer protocols. ISAKMP provides a common security
association and key establishment protocol for this wide range of security
protocols, applications, security requirements, and network environments.

ISAKMP is not bind itself bound to any specific cryptographic algo-
rithm, algorithm, key generation gener-
ation technique, or security mechanism. This flexibility is beneficial because
for a number of reasons. First, it supports the dynamic communications
environment described above. Second, the independence from specific secu-
rity mechanisms and algorithms provides a forward migration path to better
mechanisms and algorithms. When improved security mechanisms are devel-
oped or new attacks against current encryption algorithms, authentica-
tion mechanisms and key exchanges are constantly being developed that make
today's security certainties obsolete. discovered, ISAKMP will allow the
updating of the algorithms and mechanisms without having to develop a com-
pletely new KMP or patch the current one.

ISAKMP has basic requirements for its authentication and key exchanges
components. These requirements guard against denial of service, replay, replay /
reflection, man-in-the-middle, and connection hijacking attacks. This is
important because these are the types of attacks that are targeted against proto-
cols. Independence from specific security mechanisms that will eventually
be replaced by better ones
protocols. Complete Security Association (SA) support, which provides
mechanism and algorithm independence, and protection from protocol threats
are the strengths of ISAKMP.

1.1 Authentication

A very important step in establishing secure network communications is authentica-
tion au-
thentication of the entity at the other end of the communication. There are many Many
authentication mechanisms for this purpose. An example are available. Authentication mechanisms fall
into two catagories of strength - weak authen-
tication is the use and strong. Passwords are an exam-
ple of passwords. a mechanism that provides weak authentication. Reasons for this
include the fact that most users pick easy to guess passwords and when
used over an unprotected network are easily read by network sniffers.
Digital signatures signatures, such as the Digi-
tal Digital Signature Standard (DSS) and the
Rivest-Shamir-Adleman (RSA) signature signature, are public key based strong authentication mechanisms that require authen-
tication mechanisms. When using digital signatures each entity requires a trusted
third party to sign
public and properly distribute certificates. Kerberos is a private key. Certificates are an
example essential part of an authentication system that relies on a trusted third party
during the authentication. ISAKMP allows a party initiating communica-
tions to indicate which digital
signature authentication mechanism it is using and support
the message exchanges required by that mechanism. Certificates bind a specific enti-
ties identity (host, (be it host, network, user, or application) to its public keys,
keys and possibly other security-related information such as privileges,
clearances, compartments and other security-
related information. compartments. Authentication based on digital signatures
requires a trusted third party or certificate authority to create, sign
and properly distribute certificates. For more detailed information on
digital signatures, such as DSS and RSA, and certificates see [Schn94].

1.1.1 Certificate Authorities

Certificates are an essential part of strong authen-
tication mechanisms. There must be require an infrastructure available for generation, verification, man-
agement and distribution. The Internet Policy Registration Authority
(IPRA) [RFC-1422] has been established to verify,
manage direct this infrastructure for
the IETF. The IPRA certifies Policy Certification Authorities (PCA). PCAs
control Certificate Authorities (CA) which certify users and distribute certificates. Currently, subordinate
entities. Current certificate related work includes the Domain Name System Sys-
tem (DNS) Security Extensions [EK94] are being developed which will provide signed
host entity keys
in the DNS. The Public Key Infrastucture (PKIX) working group is speci-
fying an Internet profile for X.509 certificates. There is also work going go-
ing on in industry to develop X.500 Directory Services which would provide
X.509 certificates to users. The U.S. Post Office is developing a (CA)
hierarchy. The NIST Public Key Infrastructure Working Group has also been
doing work in this area. The DOD Multi Level Information System Security
Initiative (MISSI) program has begun deploying a certificate infrastruc-
ture for the U.S. Government. Alternatively, if no infrastructure exists,
the PGP Web of Trust could certificates can be used to provide user authentication authentica-
tion and privacy in a community of users who know and trust each other.

1.1.2 Entity Naming

An entity's name is its identity and is bound to its public keys in cer-
tificates. The CA MUST define the naming semantics for the certificates
it issues. See the UNINETT PCA Policy Statements [Berg] for an example
of how a CA defines its naming policy. When the certificate is verified,
the name is verified and that name will have meaning within the realm of
that CA. An example is the DNS security extensions which make DNS servers
CAs for the zones and nodes they serve. Resource records are provided for
public keys and signatures on those keys. The names associatied with the
keys are IP addresses and domain names which have meaning to entities ac-
cessing the DNS for this information. A Web of Trust is another example.
When webs of trust are set up, names are bound with the public keys. In
PGP the name is usaully the entities e-mail address which has meaning to
those, and only those, who understand e-mail (Do MCI and AOL e-mail ad-
dresses tell the casual e-mailer anything about identity?). Another web
could use an entirely different naming scheme.

1.1.3 ISAKMP Requirements

Strong authentication MUST be provided on ISAKMP exchanges. Without being
able to authenticate the entity at the other end, the Security Association
(SA) and session key established are suspect. Without authentication you
are unable to trust an entity's identification, this makes access control
questionable. Encryption (e.g. ESP) and integrity (e.g. AH) will pro-
tect subsequent communications from passive eavesdroppers, but the SA and
key may be established with an adversary who performed an active man-in-
the-middle attack and is now stealing all your personnal data.

A digital signature algorithm MUST be used within ISAKMP's authentication
component. However, ISAKMP does not specify mandate a specific certificate authority or type (e.g.
X.509 certificates), but mechanism. ISAKMP
allows an entity initiating communications to indicate which signature al-
gorithms it must allow supports. After selection of a common algorithm, the protocol
provides the messages required to support the actual authentication ex-
change. As an example, if the DSA is selected as the signature algorithm,
then the protocol provides a facility for identification of different cer-
tificate authorities, certificate authorities and types (e.g. X.509v1 certificates, PKCS
#7), and facilitate the exchange of the cho-
sen certificate type. This protocol supports the use certificates identified.

ISAKMP utilizes digital signatures, based on public cryptography, for au-
thentication. There are other strong authentication systems available,
which could be specified as additional optional authentication mechanisms
for ISAKMP. Some of these authentication systems rely on a variety of dig-
ital signatures trusted third
party called a key distribution center (KDC) to provide distribute secret session
keys. An example is Kerberos, where the strong authentication function. The DSS trusted third party is the Ker-
beros server, which holds secret keys for all clients and RSA servers within
it's network domain. A clients proof it holds it's secret key provides
its authenticaton to a server.

The ISAKMP specification does not specify the protocol for communicating
with the trusted third parties (TTP) or certificate directory services.
These protocols are examples of digital signatures which provide strong authenti-
cation. There defined by the TTP and directory service themselves
and are many others, as well. Details outside the scope of DSS, RSA, and other
signature algorithms may be found in [Schn94]. this specification.

1.2 Security Associations and Management

A Security Association (SA) is a relationship between two or more enti-
ties. The relationship entities
that describes how the entities will utilize security services to communicate communi-
cate securely. This relationship is represented by a set of information
that can be considered a contract between the entities. The information
must be agreed upon and shared between all the entities. Sometimes the
information alone is referred to as an SA, but this is just a physical instantiation in-
stantiation of the existing relationship. The existence of
the relationship, this relation-
ship, represented by the information, is what allows provides the en-
tities agreed upon se-
curity information needed by entities to communicate securely. securely interoperate. All entities enti-
ties must adhere to the SA for secure communications to be possible. The Security Parameter Index (SPI)
is When
accessing SA attributes, entities use a pointer or identifier an entity uses refered to name
as the SA. Security Parameter Index (SPI).

1.2.1 Security Associations and Registration

The types of information needed to represent SA attributes required and recommended for the IP Security (AH, ESP)
are defined in [RFC-1825]. The attributes specified for an IP Security SA
include, but are not limited to, authentication mechanisms, mechanism, cryptographic algorithms,
algorithm, algorithm mode, key length, and Initialization Vector (IV), integrity mechanisms, hash
algorithms, etc. . ISAKMP allows communicating entities to negotiate the
information needed to create an SA. It includes the ability to establish,
modify (IV).
Other protocols that provide algorithm and delete an mechanism independent security
MUST define their SA and negotiate the attributes requirements. The separation of ISAKMP
from a specific SA attributes. definition is important to ensure ISAKMP can establish
SAs for all possible security protocols and applications.

NOTE: See Appendix B for example lists a discussion of SA attributes.

1.3 Public Key Cryptography attributes that should be con-
sidered when defining a security protocol or application.

In an order to facilitate easy identification of specific attributes (e.g.
a specific encryption algorithm) among different network entites the at-
tributes must be assigned identifiers and these identifiers must be reg-
istered by a central authority. The Internet environment with large numbers Assigned Numbers Authority
(IANA) provides this function for the Internet.

1.2.2 ISAKMP Requirements

Security Association (SA) establishment MUST be part of users, there are many
ways those users can interconnect. There are also many the key management
techniques manage-
ment protocol defined for IP based networks. The SA concept is required
to support security protocols in a diverse and algorithms available dynamic networking envi-
ronment. Just as authentication and key exchange must be linked to pro-
vide assurance that the users of key is established with the network. All
users will not choose authenticated party
[DOW92], SA establishment must be linked with the same combination of capabilities. Therefore,
users need authentication and the
key exchange protocol.

ISAKMP provides the protocol exchanges to establish a way security association
between entities. First, an initial protocol exchange allows a basic set
of security attributes to determine be agreed upon. This basic set provides protec-
tion for subsequent ISAKMP exchanges. It also indicates the capabilities authentica-
tion method and key exchange that will be performed as part of the entities with which
they want to communicate. ISAKMP is intended to provide that service.

Because
protocol. If a basic set of security attributes is already in place on
the large number communicating entities the initial ISAKMP exchange may be skipped and
the key and authentication exchanges issued directly. After the basic set
of different ways Internet users can connect, security attributes has been agreed upon, initial identity authenti-
cated, and required keys generated, another security attribute exchange
takes place to establish the use complete SA which will be used for subsequent
communications by the entity that invoked ISAKMP. The basic set of public SA at-
tributes that MUST be implemented to provide ISAKMP interoperability are
defined in Appendix C. *These atributes will be moved to a separate docu-
ment to maintain separation of protocol and attributes.*

1.3 Public Key Cryptography

Public key cryptography is the most flexible flexible, scalable, and efficient way
for users to obtain the shared secrets and session keys they need.

There needed to support
the large number of ways Internet users will interoperate. Many key gen-
eration algorithms, that have different properties, are available to users
(see [DOW92] and [ANSI94]). Properties of key exchange protocols include
the key establishment method, authentication, symmetry, perfect forward
secrecy, and back traffic protection.

1.3.1 Key Exchange Properties

Key Establishment (Key Generation / Key Transport) The two common methods for
of using public key cryptography to place keys. In
the first method, user A generates a random key. The random for key establishment are key transport
and key generation. An example of key transport is then
encrypted, using the use of the RSA al-
gorithm to encrypt a public randomly generated session key algorithm (e.g. RSA), (for encrypting subse-
quent communications) with user B's pub-
lic the recipient's public key. The encrypted random ran-
dom key is then sent to user B. In the second
method, users A and B use a recipient, who decrypts it using his private
key. At this point both sides have the same session key, however it was
created based on input from only one side of the communications. The ben-
efit of the key transport method is that it has less computational over-
head then the following method. The Diffie-Hellman (D-H) algorithm illus-
trates key generation using public key cryptography. The D-H algorithm (e.g. Diffie-Hellman) to
exchange is
begun by two users exchanging public information. Then, they each use Each user then mathe-
matically combines the other's public in-
formation information along with their own secret keys se-
cret information to compute the same a shared secret value. This secret value which
they use can
be used as the a session key or the as a key encryption key for encrypting the a ran-
domly generated session key.

If public This method generates a session key cryptography based on
public and secret information held by both users. The benefit of the D-H
algorithm is that the key used in this way for exchanging or agree-
ing upon encrypting messages is based on infor-
mation held by both users. Assuming checks for weak values neither party
can force the session key to a new predetermined value. Detailed descrip-
tions of these algorithms can be found in [Schn94]. There are a number
of variations on these two key each time they communicate, then both back traffic pro-
tection generation schemes and perfect forward secrecy will these variations do
not necessarily interoperate.

Key Exchange Authentication Key exchanges may be provided. Each authenticated during the
protocol or after protocol completion. Authentication of the key exchange
during the protocol is inde-
pendent and provide when each party provides proof it has the
secret session key before the compromise end of one the protocol. Proof can be provided
by encrypting known data in the secret session key will not automatically compromise
any other keys. The second method described above during the protocol ex-
change. Authentication after the protocol must occur in subsequent commu-
nications. Authentication during the protocol is preferred as so subsequent
communications are not initiated if the secret session key
used for encrypting messages is based on information held by both not estab-
lished with the desired party.

Key Exchange Symmetry A key exchange provides symmetry if either party can
initiate the exchange and B.

1.4 exchanged messages can cross in transit with-
out effecting the key that is generated. This is desirable so that com-
putation of the keys does not require either party to know who initiated
the exchange. While key exchange symmetry is desirable, symmetry in the
entire KMP may provide a vulnerablity to reflection attacks. The entire
ISAKMP SA establishment is asymetrical.

Back Traffic Protection / Perfect Forward Secrecy

The concept Perfect forward secrecy
is provided by a key exchange protocol if disclosure of back long-term cryp-
tographic keying material (e.g. public signature keys) does not compro-
mise previously generated keys. Back traffic protection is concerned with provided by
the cryptographic
protection independent generation of previous traffic, even when cryptographic each key such that subsequent keys used to en-
crypt future traffic are compromised. The use of public key cryptography
for not
dependent on any previous key. There is a subtle difference. Past ses-
sion keys will NOT be obtainable is the establishment of cryptographic long-term key is compromised in
perfect forward secrecy; Past session keys provides will NOT be obtainable if the
current session key is compromised in back traffic protec-
tion. protecion.

The difficulty of numerical factoring of large numbers has proven that
cryptographic keys can protect information for a considerable length of
time. However, this is based on the assumption that keys used for pro-
tection protec-
tion of communications are destroyed after use and not kept for any
reason. This concept of back traffic protection is provided rea-
son.

1.3.2 ISAKMP Requirements

An authenticate key exchange MUST be supported by the inde-
pendent generation of each ISAKMP. Users SHOULD
choose additional key such that subsequent keys are not dependent establishment algorithms based on any previous key.

The concept of their require-
ments. ISAKMP does not specify a specific key exchange. Requirements
that should be evaluated when choosing a key establishment algorithm in-
clude establishment method (generation vs. transport), perfect forward secrecy is aimed at guaranteeing future
secrecy, back traffic protection, computational overhead, key escrow, and
key strength. Based on user requirements, ISAKMP allows an entity initi-
ating communications are cryptographically protected, even in the event of com-
promise of current cryptographic keys. This concept to indicate which key exchanges it supports. After
selection of perfect forward
secrecy is provided by a key exchange, the independent generation of each protocol provides the messages required
to support the actual key such that
subsequent keys are not dependent on any previous key.

1.5 establishment.

1.4 ISAKMP Protection

1.4.1 Anti-Clogging (Denial of Service)

Of the numerous security services available, protection against denial
of service always seems to be one of the most difficult to address. Phil
Karn in his Internet-Draft [Karn95] has introduced a mechanism to provide
a measure of denial of service protection through the use of a ``cookie''
exchange. This anti-clogging token (ACT) is aimed at protecting the com-
puting resources from attack without spending excessive CPU resources to
determine its authenticity. As described in [Karn95], an exchange prior
to CPU-intensive public key operations can thwart some denial of service
attempts (e.g. simple flooding with bogus IP source addresses). As noted
by Karn, absolute protection against denial of service is impossible, but
this anti-clogging token provides a technique for making it easier to han-
dle.

1.5.1 Anti-Clogging Token Creation

Phil Karn's Internet Draft [Karn95] states that cookie generation is im-
plementation dependent, but must satisfy some basic requirements:

1. The cookie must depend on

1.4.2 Connection Hijacking

ISAKMP prevents connection hijacking by linking the specific parties. authentication, key
exchange and security association exchanges. This prevents linking prevent an attacker at-
tacker from obtaining a cookie using a real IP address and
UDP port, allowing the authentication to complete and then using it jumping in
and impersonating one entity to swamp the victim with Diffie-
Hellman requests from randomly chosen IP addresses or ports.

2. It must not be possible for anyone other than the issuing
entity to generate cookies that will be accepted by that
entity. This implies that during the issuing entity must use local
secret information in key and security as-
sociation exchanges.

1.4.3 Man-in-the-Middle Attacks

Man-in-the-Middle attacks include interception, insertion, deletion, and
modification of messages, reflecting messages back at the generation sender, re-
playing old messages and subsequent
verification redirecting messages. ISAKMP features prevent
these types of a cookie. It must not be possible to deduce
this secret information attacks from any particular cookie.

3. being successful. The cookie generation function must be fast to thwart attacks
intended to sabotage CPU resources.

Karn's suggested method for creating linking of the cookie ISAKMP
exchanges prevents the insertion of messages in the protocol exchange.
The ISAKMP protocol state machine is to perform defined so deleted messages will not
cause a fast hash
(e.g. MD5) over the IP Source and Destination Address, partial SA to be created, the UDP Source and
Destination Ports state machine will clear all state
and return to idle. The state machine also prevents reflection of a locally generated secret random value. ISAKMP
requires that the mes-
sage from causing harm. The requirement for a new cookie be unique with time vari-
ant material for each new SA establishment, establishment prevents attacks that involve
replaying old messages. The ISAKMP strong authentication requirement pre-
vents an SA modify from being established with other then the intended party.
Messages may be redirected to a different destination or modified but this
will be detected and an SA delete to help prevent replay attacks, therefore we suggest adding
the date will not be established. The ISAKMP specifica-
tion defines where abnormal processing has occurred and time to recommends notify-
ing the information hashed.

1.6 appropriate party of this abnormality.

1.5 Multicast Communications

While future Internet communications will increasingly be of a multicast
nature, this document is presenting a security association and key management man-
agement protocol from the unicast point of view. It is expected that multicast mul-
ticast communications will require the same security services as unicast commu-
nications
communications and may introduce the need for additional security services. ser-
vices. The issues of distributing SPIs for multicast traffic are presented pre-
sented in
[Atki95]. [RFC-1825]. Upon agreement and implementation of a security
association protocol for the Internet unicast environment, we fully intend
to examine any additional security requirements for multicast communications. communica-
tions. For an introduction to the issues related to multicast security
consult the Internet Drafts, [Spar94a] and [Spar94b], describing Sparta's
research in this area.

2 Description of the Protocol

The Internet Security Association and Key Management Protocol (ISAKMP) de-
fines procedures and packet formats to establish (including negotiate), establish, negotiate, modify and
delete Security Associations (SA). SAs contain all the infor-
mation required information re-
quired for execution of IP security services, such as the IP Au-
thentication Authentica-
tion Header (AH), the IP Encapsulating Security Payload (ESP), and routing
protocol authentication mechanisms. ISAKMP includes packet for-
mats formats for
exchanging key generation and authentication data. These formats provide
a consistent method of transferring key and authentication data that is
independent of the key generation technique, encryption algorithm or authentication au-
thentication mechanism. These generic packets provide flexibility by
allowing the protocol to be independent of key generation techniques and
authentication mechanisms used to establish SAs.

The following sections contain the details of ISAKMP. Sections 2.1 through
2.2
2.3 cover details that are pertinent to the entire protocol. Sections 2.3 3
through 2.6 6 define the establishment, modification, and deletion services,
defined as exchanges, offered by the protocol. The appendices provide
examples of SAs and key exchanges.

2.1 ISAKMP Header Format

ISAKMP has a fixed header format. format (shown in Figure 1) followed by a vari-
able length payload, optional digital signature, and optional padding. A
fixed header simplifies parsing, pro-
viding providing the benefit of protocol parsing
software that is less complex and easier to implement parsing soft-
ware. implement. The fixed header
contains the information required by the protocol to maintain state, process pro-
cess payloads and prevent attacks (e.g. denial of service and replay).
Based on the message type type, each header is followed by a payload specific
to the message type. The payload for each message is
define defined in sections 2.3
3 through 2.6.

0 6. Following the payload portion of the ISAKMP packet is a dig-
ital signature. This field is dependent on the negotiation of Security
Association attributes and may not be present.

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Message Type ! Exchange Exch ! Vers ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! SPI Security Parameter Index (SPI) !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Initiator-Cookie !
~ Initiator-Cookie ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Responder-Cookie !
~ Responder-Cookie ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Payload ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Digital Signature ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Padding ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: ISAKMP Header Format

o Message Type (1 octet) - Indicates the type of message. A suffix of
REQ denotes a Request message of type request and an RESP suffix denotes a
Response message of type response. type. The format and processing for each message is
defined in sections 2.3 3 through 2.6. 6.

__ISAKMP_Message__Message_Type_
RESERVED 0
ISA_INIT_REQ 1
ISA_INIT_RESP 2
ISA_KE_REQ 3
ISA_KE_RESP 4
ISA_AUTH_REQ 5
ISA_AUTH_RESP 6
ISA_AUTH&KE_REQ 7
ISA_AUTH&KE_RESP 8
ISA_NEG_REQ 9
ISA_NEG_RESP 10
ISA_MODIFY_REQ 11
ISA_MODIFY_RESP 12
ISA_NOTIFY 13
ISA_DELETE 14
ISA_COMMIT 15
IANA Use 16-127
Future Use 128-255

o Exchange (1 octet) (4 bits) - indicates the type of exchange, see Sections
2.3.4 and 2.3.4 section 2.2
for a description of the Message Types exchanged in each of these
Exchange Types.

___ISAKMP_Exchange___Exchange_Type__
RESERVED 0
Base 1
Identity Protection 2
Authentication Only 3
Future Use 4 - 15

o Version (4 bits) - indicates the version of the ISAKMP protocol in
use.

o Length (2 octets) - Length of total message (header + payload) in
octets.

o SPI (4 octets) - Security Parameter Index. The receiving entity's
SPI is always in this field, except for the ISA_INIT packets. The
ISA_INIT packets contain the SPI the issuer initiator expects to receive in
all
subsequest subsequent packets.

o Initiator Cookie (16 octets) - Cookie of entity that initiated SA
establishment, SA modify or SA delete.

o Responder Cookie (16 octets) - Cookie of entity that is responding to
an SA establishment, SA modify or SA delete request request.

o Payload (variable) - The format of the payload is based on the
message type and type. These are defined in sections 2.3 3 through 2.6. 6.

o Signature - The digital signature of the initiator of the ISAKMP
message. This field will not be included on all packets and will be
determined by the negotiated SA attributes.

o Padding - This is an optional field that may be added depending on
the type of encryption algorithm. If the encryption mechanism is
based on block encryption, then this field may be necessary to ensure
the packet is a specific size.

2.1.1 General Message Processing

Every ISAKMP message has basic processing applied to insure protocol re-
liability
liability, and to minimize threats, such as denial of service and replay at-
tacks.
attacks.

When issuing transmitting an ISAKMP packet: packet, the transmitting entity (initiator or
responder) does the following:

1. Sets a timer and initializes a retry counter counter.

2. If the timer expires expires, the message ISAKMP packet is resent and the retry
counter is decremented.

3. If the retry counter reaches zero (0), the event event, RETRY LIMIT
REACHED, is logged in the appropriate system audit file.

4. Clears The ISAKMP protocol machine clears all state states and return returns to IDLE.

When an ISAKMP packet is received: received, the receiving entity (initiator or re-
sponder) does the following:

1. Verify Verifies the Initiator and Responder ``cookies''. If the cookie
validation fails, the message is discarded and the following actions
are taken:

(a) The event, INVALID COOKIE, is logged in the appropriate ``cookie''. system
audit file.

(b) No response is sent to the initiating entity. This will cause
the transmission timer of the initiating entity to expire and
force retransmission of the message.

2. Check exchange type and message fields the Message Type field to confirm they it is valid. If the Message
Type field validation fails, the message is discarded and the
following actions are valid
types. taken:

(a) The event, INVALID MESSAGE TYPE, is logged in the appropriate
system audit file.

(b) No response is sent to the initiating entity. This will cause
the transmission timer of the initiating entity to expire and
force retransmission of the message.

3. Check SPI the Exchange field to ensure confirm it is valid for the exchange being preformed.

4. Message Type
requested. If any of these fields fails its check, the Exchange field validation fails, the message is discarded.

Log Event
discarded and the following actions are taken:

(a) The event, INVALID EXCHANGE TYPE, is logged in the appropriate
system audit file.

(b) No response is sent to the message orginator.

5. initiating entity. This will cause
the transmission timer of the initiating entity to expire and
force retransmission of the message.

4. Check SPI to ensure it is valid for the Message Type and Exchange
being performed. If all fields pass the checks, SPI validation fails, the message payload is processed.

Individual message processing (described in sections 2.3 through 2.6)
may result in
discarded and the message being invalidated, in which case:

Log Event following actions are taken:

(a) The event, INVALID SPI, is logged in the appropriate system audit
file.

(b) No response is sent to the initiating entity. This will cause
the transmission timer of the initiating entity to expire and
force retransmission of the message.

5. The message orginator.

A payload is processed. Individual message processing is
described in sections 3 through 6. Depending on the Message Type, a
valid message results in a response being sent to the message
orginator. transmitting
entity (message originator). The procedures for sending these
responses are also outline in sections 3 through 6.

2.2 ISAKMP Details Packet Exchanges

The Exchange field in the ISAKMP header currently has three values de-
fined: the base exchange, the identity protection exchange, and the au-
thentication only exchange. These exchanges define the flow of the ISAKMP
packets during SA establishment. The diagrams in 2.2.1, 2.2.2, and 2.2.3
show the packet exchange ordering for each exchange type and provide basic
notes describing what has happened after each packet exchange.

2.2.1 Base Exchange

Sections 3.1 through 3.3 describe the three basic phases: SA Initial-
ization, Key Exchange and Authentication, and SA Negotiation, that com-
prise the base exchange. The base exchange contains the minimum number of
packet exchanges in order to reduce latency associated with SA establish-
ment.

Base Exchange
____Initiator____Direction_____Responder____ Note
ISA_INIT_REQ =>
<= ISA_INIT_RESP
Basic SA selected
ISA_AUTH&KE_REQ =>
<= ISA_AUTH&KE_RESP
Identity Verified
Key Generated
Encryption Begun
ISA_NEG_REQ =>
<= ISA_NEG_RESP SA Completed
(optional) ISA_COMMIT =>

2.2.2 Identity Protection Exchange

The identity protection exchange starts and ends the same as the base ex-
change, but separates the key exchange payload and the authentication pay-
loads into separate packets. In this exchange, the key exchange is trans-
mitted first followed by the strong authentication exchange. The benefit
of this exchange is the ability to communicate with a person without dis-
closing either party's identity to passive attackers on the network.

The ISA_KE_REQ and ISA_KE_RESP packets used for the key exchange portion of
this exchange contain an ISAKMP header followed by the key exchange pay-
load. The ISA_AUTH_REQ and ISA_AUTH_RESP packet used for the authentication
portion of this exchange contain an ISAKMP header followed by the authen-
tication payload.

Identity Protection Exchange
__Initiator___Direction___Responder___ Note
ISA_INIT_REQ =>
<= ISA_INIT_RESP
Basic SA selected
ISA_KE_REQ =>
<= ISA_KE_RESP
Key Generated
Encryption Begun
ISA_AUTH_REQ =>
<= ISA_AUTH_RESP
Identity Verified
ISA_NEG_REQ =>
<= ISA_NEG_RESP SA Completed
(optional) ISA_COMMIT =>

2.2.3 Authentication Only Exchange

The authentication only exchange starts and ends the same as the base ex-
change. In this exchange, the authentication information is the only in-
formation transmitted. The benefit of this exchange is the ability to
perform only an authentication exchange without the computational expense
of computing keys. Using this exchange, none of the transmitted informa-
tion will be encrypted.

The ISA_AUTH_REQ and ISA_AUTH_RESP packet used for the authentication only
exchange contain an ISAKMP header followed by the authentication payload.

Identity Protection Exchange
__Initiator___Direction___Responder___ Note
ISA_INIT_REQ =>
<= ISA_INIT_RESP
Basic SA selected
ISA_AUTH_REQ =>
<= ISA_AUTH_RESP
Identity Verified
ISA_NEG_REQ =>
<= ISA_NEG_RESP SA Completed
(optional) ISA_COMMIT =>

2.3 ISAKMP Details

2.3.1 Security Association Attributes

A Security Association (SA) is a relationship between two enities entities that
describes how they will utilize security services. This relationship is
represented by a collection of security related information. The SA At-
tributes are the individual elements that comprise all security relevant
information necessary to form the SA.

The following syntax encodes defines the security attributes to be exchanged by
ISAKMP. This syntax is used in the ISA_INIT_REQ, ISA_INIT_RESP, ISA_NEG_REQ,
ISA_NEG_RESP, ISA_MOD_REQ, and ISA_MOD_RESP messages. The syntax groups se-
curity attributes needed to perform a security function into either an SA
set or SA list format. The set format must MUST be supported by ISAKMP implementa-
tions. imple-
mentations. The list format is an optional format.

Security Associations Sets The set format groups all necessary attributes
together. Each set has a unique identifier (Set Number), supported security secu-
rity service (Supports), such as IP AH, IP ESP, OSPF authentication, and
a list of Attribute Classes and Attribute Types. The Attribute Class is
the broad category of Attribute Type, such as encryption algorithms. Attribute At-
tribute Type is a specific attribute identifier. DES is an example of an
attribute type for the encryption algorithm attribute class. A set has
only one instance of an Attribute Class and one type for that class. This
syntax maintains flexibility by allowing many different (and some still
undefined) types of SA attributes to be exchanged.

The figure below

Figure 2 depicts the syntax for exchanging security attributes us-
ing using
the set format. It shows a single set from which multiple sets would be
grouped for a specific message type.

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Set Number ! Supports ! Number Num of Attr !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Attribute Class ! Attribute Type !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ..... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Attribute Class ! Attribute Type !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: Generic Set Exchange Format

o Set number (1 octet) - Unique identifier for each proposed set

o Supports (1 octet) (2 octets) - Security service proposed set supports.
Examples are IP AH, IP ESP, and OSPF authentication

o Number of Attributes (2 octets) (1 octet) - Number of attributes attribute classes
contained in the proposed set

o Attribute Class (2 octets) - examples are Encryption Algorithms, Key
Exchange Algorithms Algorithms, Authentication Mechanisms

o Attribute Type (2 octets) - examples of attribute type types for the
encryption algorithms attribute class are DES, Triple DES, and IDEA.

The size of a set formatted exchange is 4 octets + (Number of Attrs Attribute
Classes * 4 octets). Computing the size of a particular set allows determining the
determination of the beginning of the next set without completely parsing
the current set,
should set. This is necessary when it is determined that the current
set is not be an acceptable SA set. This will improve the performance of SA
Attribute determination.

Security Association Lists The SA list format presents several attribute
types for an attribute class. Each type within the class is then ordered
to indicate its prece-
dence. precedence. Specifically, the first attribute type is the
highest priority type, followed by other choices. Each subsequent choice are
is listed in descending priority order. An attribute type must be chosen from
for each at-
tribute attribute class to establish a complete SA.

The figure below

Figure 3 shows the sytax syntax for the optional list exchange format.
Note that multiple attribute types appear within an attribute class. The
number num-
ber of types is determined from by the Count field. The number of Attribute
Types within an Attribute Class will depend on what is supported by the
local machine.

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Attribute Class ! Count !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Attribute Type ! Attribute Type !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Attribute Type ! Attribute Type !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: Generic List Exchange Format

o Attribute Class (2 octets) - Examples are Encryption Algorithms, Key
Exchange Algorithms

o Count - Number of proposed types Attribute Types for a class the given Attribute
Class

o Attribute Type (2 octets) - Presented in descending priority order

Appendix B presents an outline containing a more comprehensive set listing of SA
attributes. These sets This listing of attributes are initial definitions and are pre-
sented
presented to stimulate thought and discussion on SAs. The final set of SA
attributes should for
a protocol SHOULD be defined in a separate RFC that protocol so additions or modifica-
tions to the attributes do not require a modification to the Internet Key
Management Protocol (IKMP) RFC and vice versa. An SA container object and
SA attribute definitions should become part of the Management Information
Base (MIB), see [RFC-1213], in a separate protected section called the Se-
curity MIB. IKMP should emulate For example, Appendix C
describes the SNMP concept of separate RFCs sample security associations for the
protocol ISAKMP and the information managed. SA attribute identifiers MAY be de-
fined using the syntax in [RFC-1155] IPSP ESP and [RFC-1212].

2.2.2 AH.

2.3.2 Transport Protocol

The User Datagram Protocol (UDP) is the transport protocol for ISAKMP. UDP
checksumming discards UDP packets with an incorrect or zero (0) checksum.
ISAKMP is unaware of the discard, but will resend the packet when its re-
send timer expires.

2.2.3

2.3.3 RESERVED Fields

The existence of RESERVED fields are strictly used to preserve byte
alignement. All RESERVED fields in the ISAKMP protocol MUST be set to
zero (0) when a packet is issued. The receiver SHOULD check the RESERVED
fields for zero (0) and discard the packet if other values are found.

2.3

2.3.4 Anti-Clogging Token (``Cookie'') Creation

Phil Karn's Internet Draft [Karn95] states that cookie generation is im-
plementation dependent, but must satisfy some basic requirements:

1. The cookie must depend on the specific parties. This prevents
an attacker from obtaining a cookie using a real IP address and
UDP port, and then using it to swamp the victim with Diffie-
Hellman requests from randomly chosen IP addresses or ports.

2. It must not be possible for anyone other than the issuing
entity to generate cookies that will be accepted by that
entity. This implies that the issuing entity must use local
secret information in the generation and subsequent
verification of a cookie. It must not be possible to deduce
this secret information from any particular cookie.

3. The cookie generation function must be fast to thwart attacks
intended to sabotage CPU resources.

Karn's suggested method for creating the cookie is to perform a fast hash
(e.g. MD5) over the IP Source and Destination Address, the UDP Source and
Destination Ports and a locally generated secret random value. ISAKMP
requires that the cookie be unique for each SA establishment, SA modify
and SA delete to help prevent replay attacks, therefore the date and time
MUST be added to the information hashed.

2.3.5 SA Flags Field

The SA Flags field may be set by the entity that initiated the negotia-
tion to indicate that the ISA_COMMIT packet will follow the completion of
the protocol exchange. The SA Flags field exists only in the ISA_INIT and
ISA_NEG packets. If the initiating entity sets the flag, the responding
entity cannot reset it. If the initiating entity does not set the flag,
the responding entity may set it, thereby, forcing the initiating entity
to issue an ISA_COMMIT packet. If neither entity sets the flag, then the
ISA_COMMIT packet will not be issued. To set the flag the Least Signifi-
cant Bit (LSB) in the SA Flags field is set to one (1) . All other bits
in the SA Flags field are zero (0).

3 Security Association Establishment

Security Association (SA) Establishment is the process of agreeing upon
and exchanging all the security information that is required in an SA. The
following sections,
2.3.1 3.1 to 2.3.3, 3.3, describe the three basic phases, -- phases that com-
prise SA Establishment: SA Initialization,
key Key and Authentication information infor-
mation exchange, and SA Negotiation --, that
comprise SA Establishment.

2.3.1 Negotiation.

3.1 Security Association Initialization

The initialization exchange of SA establishment is composed of the
ISA_INIT_REQ and ISA_INIT_RESP packets. packets shown in figure 4. The ISA_INIT packets pack-
ets exchange ``cookies'', and options for a key generation technique, an
encryption algorithm and an authentication mechanism. The ``cookies''
are used to prevent replay and denial of service attacks. Authentication
and encryp-
tion encryption for the ISAKMP exchanges is are provided by the authentication
mechanism and encryption algorithm selected. The key generation technique
selected creates keys for use by the authentication mechanism and encryption al-
gorithm. encryp-
tion algorithm. The keys may also be used either as any of the following: ac-
tual session keys, to create the session keys, or to protect the exchange
of the actual session keys for the SA. If the key, encryption algorithm,
and authentication mechanism are only used to protect ISAKMP exchanges exchanges,
then new options can be picked dur-
ing during the negotiation phase (described in
Section 2.3.3) 3.3) for use in protect-
ing protecting the actual data communications. If encryption en-
cryption is not required for the
SA SA, the encryption algorithm options need are
not be exchanged.

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ISAKMP Header ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! SA Syntax Type! SA Flags ! Num of Sets # Sets/Lists ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SA Attribute Set Set/List #1 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SA Attribute Set Set/List #2 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SA Attribute Set Set/List #N ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: ISA_INIT_REQ and ISA_INIT_RESP Packet Format

o SAKMP ISAKMP Header - Described in Section 2.1

o SA Syntax Type (1 octet) - Presentation format of SAs

_SA_Syntax__SA_Syntax_Type_
RESERVED 0
Set 1
List 2

o SA Flags (1 octet) - Flags specific to an SA service. The SA Flags
field is zero (0) See section
2.3.5 for the ISA_INIT messages. details.

o Number of Sets (1 octet) - Number of SA Attribute Sets being proposed
o SA Attributes (variable) - A list of SA Attributes. The SA Attribute
specifications are discussed in Section 2.2.1. 2.3.1.

3.1.1 SA Initialization Procedures

When issuing an ISA_INIT_REQ message: message, the initiating entity does the fol-
lowing:

1. Create initiator cookie. See Section 1.5.1 2.3.4 for details.

2. Generate a unique pseudo-random SPI SPI. See Section 2.1 for future communications with
the initiating host. details.

3. Construct an ISA_INIT_REQ packet. If the initiator will send an
ISA_COMMIT message upon completion of the SA establishment, then the
SA Flags field MUST be set (see section 2.3.5 and 3.4).

4. Send Transmit the packet to the destination host as described in Section
2.1.1.

When an ISA_INIT_REQ message is received: received, the receiving entity does the
following:

1. Check the ISAKMP header as described in Section 2.1.1.

2. Unpack the ISA_INIT_REQ payload and determine the highest priority
attribute set (or attribute list) supported. If the proposed
attribute set (or list) is rejected, then the protocol machine must
clear all state and return to IDLE.

3. Create responder cookie. See Section 2.3.4 for details.

4. Create Generate a unique pseudo-random SPI SPI. See Section 2.1 for future communications with the
responding host. details.

5. Construct an ISA_INIT_RESP packet. If the responder wants to request
that an ISA_COMMIT message be sent upon completion of the SA
establishment, then the SA Flags field MUST be set (see section 2.3.5
and 3.4).

6. Send Transmit the packet to the initiating host as described in Section
2.1.1.

When an ISA_INIT_RESP message is received: received, the receiving entity (original
initiator) does the following:

1. Check the ISAKMP header as described in Section 2.1.1.

2. Unpack the ISA_INIT_RESP payload.

3. Determine if the attribute set (or list) selected by the responder is
valid. If the attribute set (or list) is invalid or the responder
rejected all proposed attribute sets:

Log Event sets (or lists), the receiving entity
does the following:

(a) The event, INVALID ATTRIBUTES, is logged in the appropriate
system audit file.

(b) Clear all state and return to IDLE.

4. Any further communication
must start the SA initialization procedures from the beginning.

If the attribute set (or list) is valid, the receiving entity does
the following:

(a) Configure protocol machine based on attribute set selected.

(b) Transition to Key and Authentication Phase.

2.3.2 Key and Key Exchange (see Section 3.2).

3.2 Authentication Phase

The and Key Exchange

During the authentication and key exchange phase exchange phase, information required to
confirm the identities of the parties wishing to establish the SA and
establish es-
tablish a session key for use during the SA establishment. Based establishment is exchanged.
Depending on
user preferences the key exchange algorithm, the original key may be used during dur-
ing data communications or a new one may be created/exchanged created and exchanged during
the negotiation phase, described phase (described in section 2.3.3, for use 3.3). This original or new
key would be used in protecting the actual data communications.

The packets that carry the authentication and key exchange payloads have
the format shown in Figure 5. When the ISA_AUTH&KE_REQ and ISA_AUTH&KE_RESP
packets are used, the Authentication Payload SHOULD be processed first to
strongly authenticate the packet issuer, followed by the processing of
the Key Exchange Payload. The authentication and key exchange payloads
(shown in Figures 6 and 7) are general formats which support many types
of authentication and key exchange and authentication. mechanisms. The detailed specification
of these fields are will be specified in companion RFCs. These companion RFCs
will define the standard authentication and key exchange mechanisms that
need to be implemented and to assure compliance with this specification.

The packets that carry the authentication and key exchange payloads have
the format shown below. When the ISA_AUTH&KE_REQ and ISA_AUTH&KE_RESP pack-
ets are used the authentication payload SHOULD be processed first to
strongly authenticate the packet issuer, before the key generation pro-
cessing is executed. In the ISA_AUTH_REQ and ISA_AUTH_RESP packets the key
exchange payload is not present. In the ISA_KE_REQ and ISA_KE_RESP packets
the authentication payload is not present.

Figure 5: ISA_AUTH&KE_REQ and ISA_AUTH&KE_RESP Packet Format

Strong

3.2.1 Authentication Details Payload Format

This section specifies the encoding of the authentication payload for the
ISA_AUTH_REQ, ISA_AUTH_RESP, ISA_AUTH&KE_REQ, and ISA_AUTH&KE_RESP messages.
As described in section 2.2.3, when the ISA_AUTH_REQ and ISA_AUTH_RESP pack-
ets are transmitted alone, the key exchange payload is not present. The
format of these messages is shown in Figure 6.

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Authentication Authority ! Reserved !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Authentication Type ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
! Authentication Data !
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 6: Authentication Payload Format

o Authentication Authority (2 octets) - Indentifies This field identifies the party
that generated the certificates used for authentication. Authorities
must be assigned an identifier by the Internet Assigned Numbers
Authority (IANA). Before being assigned an identifier, an authority
must publish an RFC defining the authority's domain. [RFC-1422]
describes the Internet Policy Registration Authority (IPRA) and the
procedures for achieving this registration.

If PGP certificates, based on the ``web of trust'', are carried in
the authentication payload the Authentication Authority value is one
(1).

Examples

Example certificate authorities that would have to register for an
identifier are:

-- RSA Commercial Certificate Authority
(https://www_csc.rsa.com/netsite)
(http://www_csc.rsa.com/netsite)

-- Stable Large E-mail Database (SLED) (http://www.four11.com)

-- U.S. Postal Service.

o Authentication Type (2 octets) - Indicates This field indicates the
authentication payload format. This field is used by authentication
authorities that support more than one certificate type. The
authentication types supported by an authentication authority must be
defined in the RFC required for authentication authority
registration. Examples are:

-- RSA certificates

-- PGP certificates

-- DSS certificates

-- DNS Signed Keys

-- Kerberos Tokens

-- X.509 certificates

o Length (2 octets) - Length of the Authentication Data field in
octets.

o Authentication Data (variable) - Actual authentication data. Type The
type of certificate is indicated by the Authentication type Type field.

3.2.2 Key Exchange Details Payload Format

A variety of key exchanges can be supported in the key exchange phase.
Some examples of key exchanges which may be used in this protocol are
Diffie-Hellman, the enhanced Diffie-Hellman key exchange described in
X9.42 [ANSI94], the key exchange on the FORTEZZA card, and the RSA-based
key exchange used by PGP. This protocol will also support the government key exchanges
that include key escrow requirement, or data recovery techniques, but does not mandate its
their use.

The encoding of the key exchange payload is dependent on the specific key
exchange and therefore and, therefore, is not specified in this Internet draft. Each
key exchange must define the following information: (a) System parame-
ters, (b) Key establishment algorithm, and (c) Key derivation procedure
(dependent on key exchange type).

There can be both public and private key generation techniques. Both
types must register with IANA to obtain a Key Exchange Identifier (KEI).
Before pub-
lic published public key exchanges can obtain a KEI, an RFC defining
the key exchange pay-
load payload format and key generation procedures MUST be submitted. sub-
mitted. Private key exchanges are not REQUIRED to provide SHOULD be documented in an RFC when registering regis-
tering for a KEI.

Example

As described in section 2.2.2, when the ISA_KE_REQ and ISA_KE_RESP packets
are transmitted alone, the authentication payload is not present. Once
the key exchange is completed, then the authentication payload encodings are shown is sent
separately using the format described in Appendix A. section 3.2.1

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! KEI ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
! Key Exchange Payload !
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 7: Key Exchange Payload Format

o KEI (2 octets) - Key Exchange Identifier

o Length (2 octets) - Length of payload in octets

o Key Exchange Payload (variable) - Data (i.e. public values) required
to create session key.

ISA_AUTH&KE

3.2.3 Authentication and Key Exchange Procedures

When issuing an ISA_AUTH&KE_REQ packet: packet, the initiating entity will do the
following:

1. Create the ISAKMP Header.

2. Create the authentication payload.

3. Create the key exchange payload based on KEI.

4. Construct an ISA_AUTH&KE_REQ packet.

5. Generate an authentication signature using the authentication
attributes and options selected in the initialization phase.

2. Create key exchange payload based on KEI.

3. Construct an ISA_AUTH&KE_REQ packet.

4. Send

6. Transmit the packet to the responding host as described in Section
2.1.1.

When an ISA_AUTH&KE_REQ packet is received: received, the receiving entity will do
the following:

1. Check the ISAKMP header as described in Section 2.1.1.

2. Unpack ISA_AUTH&KE_REQ packet.

3. Verify Initiator's the initiator's signature.

If verification fails
Log Event The ISA_AUTH&KE_REQ packet is
processed and the calculated signature is compared to the signature
contained in the appropriate system file.

Terminate with error.

ELSE

Discard ISA_AUTH&KE_REQ packet.

Log Event If these signatures are not
identical, the message is discarded and the following actions are
taken:

(a) The event, INVALID SIGNATURE, is logged in the appropriate system
audit file.

RETURN

(b) No response is sent to WAIT for the initiating entity. This will cause
the transmission timer of the initiating entity to expire and
force retransmission of the message.

3. Unpack the ISA_AUTH&KE_REQ state. packet.

4. Create the ISAKMP Header.

5. Create the authentication payload.

6. Create the key exchange payload based on KEI.

7. Construct an ISA_AUTH&KE_RESP packet.

8. Generate an authentication signature, to authenticate responder to
initiator, using the authentication attributes and options selected.

5. Create key exchange payload for initiator based on KEI.

6. Construct an ISA_AUTH&KE_RESP packet.

7. Send

9. Transmit the packet to the initiating host as described in Section
2.1.1.

10. Begin key calculation in the background. background, if necessary.

When an ISA_AUTH&KE_RESP message is received: received, the receiving entity (origi-
nal initiator) will do the following:

1. Check the ISAKMP header as described in Section 2.1.1.

2. Verify Responder's the initiator's signature.

If verification fails, either:

Log Event The ISA_AUTH&KE_RESP packet is
processed and the calculated signature is compared to the signature
contained in the appropriate system file.

Terminate with error.

ELSE

Discard ISA_AUTH&KE_RESP packet.

Log Event If these signatures are not
identical, the message is discarded and the following actions are
taken:

(a) The event, INVALID SIGNATURE, is logged in the appropriate system
audit file.

RETURN

(b) No response is sent to WAIT for ISA_AUTH&KE_RESP state. the initiating entity. This will cause
the transmission timer of the initiating entity to expire and
force retransmission of the message.

3. Calculate key. key, if necessary.

4. Transition to Security Association Negotiation Phase.

2.3.3 Negotiation.

3.3 Security Association Negotiation Phase

The SA Negotiation phase allows the initiating entity to present SA at-
tributes,
tributes that it wishes to use for secure communications, communications to a responding respond-
ing entity. These SA attributes may included include additional options for the at-
tributes
attributes agreed upon during the initialization phase, as well as selection
of the additional ad-
ditional attributes required for an SA. The REQUIRED and REC-
OMMENDED As an example, the SA parameters parame-
ters for the IP AH and IP ESP security mechanisms are cited in the Security Secu-
rity Architecture for the Internet Protocol [Atki95].

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ISAKMP Header ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! SA Syntax Type! Num of Sets ! SA Flags ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SA Attribute Set #1 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SA Attribute Set #2 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SA Attribute Set #N ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ [RFC-1825]. The format for
the ISA_NEG_REQ and ISA_NEG_RESP Packet Format

o SA Msg Type (1 octet) - Defined packets is the same as the ISA_INIT_REQ and
ISA_INIT_RESP shown in Section 2.3.1.

o Num of Sets (1 octet) - Number of Attribute Sets being proposed

o SA Flags (1 octet) - Flags specific to an SA service. See Section
2.3.3 for flag settings Figure 4. All fields shown in Figure 4 exist for
the ISA_NEG messages.

o SA Attributes (variable) - A list of SA attributes. SA Attribute
specifications are discussed in section 2.2.1. ISA_NEG_REQ and ISA_NEG_RESP packets.

3.3.1 SA Negotiation Procedures

When issuing an ISA_NEG_REQ packet: packet, the initiating entity does the follow-
ing:

1. Determine SA attributes to be negotiated. This may include changing
or confirming the
some attributes from the original SA initialization phase. initialization.

2. Encrypt and/or sign ISA_NEG_REQ payload only (not header).

3. Construct an ISA_NEG_REQ packet. If the initiator will send an
ISA_COMMIT message upon completion of the SA establishment, then the
SA Flags field MUST be set (see section 2.3.5 and 3.4).

3. Depending on the SA Attributes established in the SA initialization
phase, apply the agreed upon security services.

(a) If the SA requires authentication, the ISA_NEG_REQ packet is pro-
cessed (or signed) and the signature placed as noted in Figure 1.

(b) If the SA requires encryption and the encryption algorithm is a
block encryption algorithm, then padding up to the block size
MUST be placed as noted in Figure 1.

4. Send Transmit the packet to the responding host as described in Section
2.1.1.

When an ISA_NEG_REQ packet is received: received, the receiving entity does the fol-
lowing:

1. Check the ISAKMP header as described in Section 2.1.1.

2. Decrypt Depending on the SA Attributes, apply the agreed upon security
services.

(a) If the SA requires encryption, decrypt the ISA_NEG_REQ payload and verify signature.
Signature. If the decryption fails, the message is discarded and
the following actions are taken:

i. The event, DECRYPTION FAILED, is logged in the appropriate
system audit file.

ii. No response is sent to the initiating entity. This will
cause the transmission timer of the initiating entity to
expire and force retransmission of the message.

(b) If the SA requires authentication, the ISA_NEG_REQ packet is
processed and the calculated signature is compared to the
signature contained in the ISA_NEG_REQ packet. If these signatures
are not identical, the message is discarded and the following
actions are taken:

i. The event, INVALID SIGNATURE, is logged in the appropriate
system audit file.

ii. No response is sent to the initiating entity. This will
cause the transmission timer of the initiating entity to
expire and force retransmission of the message.

3. Unpack the ISA_NEG_REQ packet payload and determine the highest
priority SA attributes supported. If none of the SA attribute
options are supported, the ISA_NEG_RESP packet will have the value zero
(0) in the Number of Sets field and an SA will not be established.

4. If the SA negotiation is requesting a key change or new
authentication mechanism, then, then generate the appropriate information
and include it as an attribute/option attribute in the ISA_NEG_RESP payload.

5. Encrypt and/or sign ISA_NEG_RESP payload only (not header).

6. Construct an ISA_NEG_RESP packet. If the responder wants to request
that an ISA_COMMIT message be sent upon completion of the SA
establishment, then the SA Flags field MUST be set (see section 2.3.5
and 3.4).

6. Depending on the SA Attributes, apply the agreed upon security
services.

(a) If the SA requires authentication, the ISA_NEG_RESP packet is
processed and the signature placed as noted in Figure 1.

(b) If the SA requires encryption and the encryption algorithm is a
block encryption algorithm, then padding up to the block size
MUST be placed as noted in Figure 1.

7. Send Transmit the packet to the initiating host as described in Section
2.1.1.

8. If required, begin calculation of the new session key in the
background.

9. Transition to SA Negotation Conclusion. Conclusion (see Section 3.4).

When an ISA_NEG_RESP message is received: received, the receiving entity (original
initiator) does the following:

1. Check the ISAKMP header as described in Section 2.1.1.

2. Decrypt Depending on the SA Attributes, apply the agreed upon security
services.

(a) If the SA requires encryption, decrypt the ISA_NEG_RESP payload and verify signature.
Signature. If the decryption fails, the message is discarded and
the following actions are taken:

i. The event, DECRYPTION FAILED, is logged in the appropriate
system audit file.

ii. No response is sent to the initiating entity. This will
cause the transmission timer of the initiating entity to
expire and force retransmission of the message.

(b) If the SA requires authentication, the ISA_NEG_RESP packet is
processed and the calculated signature is compared to the
signature contained in the ISA_NEG_RESP packet. If these
signatures are not identical, the message is discarded and the
following actions are taken:

i. The event, INVALID SIGNATURE, is logged in the appropriate
system audit file.

ii. No response is sent to the initiating entity. This will
cause the transmission timer of the initiating entity to
expire and force retransmission of the message.

3. Unpack the ISA_NEG_RESP payload and verify the SA attributes selected
by responder are valid. If response is the attribute sets (or lists) are invalid
or the responder rejected all proposed SA
Attributes:

Log Event attribute sets (or lists), the
receiving entity does the following:

(a) The event, INVALID ATTRIBUTES, is logged in the appropriate
system audit file.

(b) Clear all state and return to an IDLE.

If the attribute set (or list) is valid, the receiving entity does
the following:

(a) Configure the protocol machine based on the attribute set (or
list) selected.

4. If required, begin calculation of the new session key in the
background.

5. Transition to SA Negotiation Conclusion. Conclusion (see Section 3.4).

3.4 SA Negotiation Conclusion

SA Commit Message

The SA Commit negotiation concludes with the transmittal of the optional
SA_COMMIT packet. This is determined by the setting of the SA Flags
field. The SA_COMMIT message allows the initiating entity to inform the
responding party that it has completed the processing required to set-up
the SA and therefore, secure communications may begin.

The Least Significant Bit (LSB) in the SA Flags field is set to one (1)
in the ISA_NEG packet if an ISA_COMMIT packet is issued and zero (0) if the
ISA_COMMIT packet is not issued. All other bits in the SA Flags field are
zero (0).

The SA Flags field may be set by the entity that initiated the negotia-
tion to indicate that the ISA_COMMIT packet will follow the negotiation
exchange. If the initiating entity sets the flag the responding entity
can not reset it. If ini-
tiating the initiating entity SA establishment does not set the flag have the re-
sponding entity ability to queue incoming
data it may set it, thereby forcing receive prior to its completion of SA establishment process-
ing, then it requires the initiating responding entity to issue wait for an ISA_COMMIT packet. If neither entity sets the flag then the ISA_COMMIT
packet will not be issued.

The ISA_COMMIT packet is the ISAKMP header with no payload. SA_COMMIT mes-
sage before sending data. The SPI is set to transmittal of the Responder SPI.

Transmiting ISA_COMMIT packet is optional op-
tional and determined by the policy of the parties establishing the SA.
All implementations MUST be able to gen-
erate, generate, transmit, and receive this
message.

SA_Negotiation

The ISA_COMMIT packet is the ISAKMP header, described in section 2.1, with
no payload.

3.4.1 SA Negotiation Conclusion Procedures

When issuing an ISA_COMMIT packet, the initiating entity does the follow-
ing:

1. Both initiator and responder place Construct an ISA_COMMIT packet (ISAKMP Header).

2. Depending on the SA Attributes established in appropriate database for the SA initialization
phase, apply the agreed upon security service it supports.

2. Based on services.

(a) If the SA Flags field, requires authentication, the initiator constructs an ISA_COMMIT
packet. packet is pro-
cessed (or signed) and the signature placed as noted in Figure 1.

(b) If the SA requires encryption and the encryption algorithm is a
block encryption algorithm, then padding up to the block size
MUST be placed as noted in Figure 1.

3. Initiator sends Transmit the packet to the responding host as described in Section
2.1.1.

4. Clear all state and return to IDLE.

When responder received an ISA_COMMIT packet it checks is received, the receiving entity does the fol-
lowing:

1. Check the ISAKMP header as described in Section section 2.1.1.

5. Clear all state and return to IDLE.

2.3.4 Packet Exchanges

The ``Exchange'' field in

2. Depending on the ISAKMP header currently has two values de-
fined, SA Attributes, apply the base exchange (BASE) and agreed upon security
services.

(a) If the anonomous exchange (ANON). These
exchanges define SA requires encryption, decrypt the flow of ISA_COMMIT Signature.
If the ISAKMP packets during SA establishment. decryption fails, the message is discarded and the
following actions are taken:

i. The diagrams event, DECRYPTION FAILED, is logged in 2.3.4 and 2.3.4 shows the appropriate
system audit file.

ii. Because the ISA_COMMIT packet exchange ordering for
each exchange type and provides basic notes describing what has happened
after each packet exchange.

Base Exchange

The previous sections, 2.3.1 to 2.3.3, described is a unidirectional message a
retransmission will not be performed. Because the three basic phases,
-- SA Initialization, key and authentication information exchange, and
SA negotiation --, is
established, we recommend that comprise communications can proceed,
however, the BASE exchange. The base exchange
contains local security policy will dictate the minimum number of
procedures for continuing. We recommend that an ISA_NOTIFY
packet exchanges in order to reduce latency
associated with SA establishment.

Base Exchange
___Initiator___________Responder_____ Note
ISA_INIT_REQ =>
<= ISA_INIT_RESP
Basic SA selected
ISA_AUTH&KE_REQ =>
<= ISA_AUTH&KE_RESP
Identity Verified
Key Generated
Encryption Begun
ISA_NEG_REQ =>
<= ISA_NEG_RESP SA Completed
(optional) an Error Message Type (see Section 6) be sent to
the originator of the ISA_COMMIT =>

Identity Protection packet.

(b) If the SA Establishment Variation

The identity protect exchange starts and ends requires authentication, the same as ISA_COMMIT packet is
processed and the base ex-
change, but separates calculated signature is compared to the key exchange payload and
signature contained in the authentication pay-
loads into separate packets. In this exchange ISA_COMMIT packet. If these signatures
are not identical, the key exchange message is trans-
mited first followed by discarded and the strong authentication exchange. following
actions are taken:

i. The benefit
of this exchange event, INVALID SIGNATURE, is logged in the ability to communicate with appropriate
system audit file.

ii. Because the ISA_COMMIT packet is a person without dis-
closing either party's identity to passive attackers on unidirectional message a
retransmission will not be performed. Because the network.

The ISA_KE_REQ and ISA_KE_RESP packets used for SA is
established, we recommend that communications can proceed,
however, the key exchange in this
variation contain an ISAKMP header followed by local security policy will dictate the key exchange payload.

The ISA_AUTH_REQ and ISA_AUTH_RESP packet used
procedures for the authentication ex-
change in this variation contain continuing. We recommend that an ISAKMP header followed by ISA_NOTIFY
packet with an Error Message Type (see Section 6) be sent to
the originator of the authen-
tication payload.

Identity Protection Exchange
__Initiator________Responder___ Note
ISA_INIT_REQ =>
<= ISA_INIT_RESP
Basic SA selected
ISA_KE_REQ =>
<= ISA_KE_RESP
Key Generated
Encryption Begun
ISA_AUTH_REQ =>
<= ISA_AUTH_RESP
Identity Verified
ISA_NEG_REQ =>
<= ISA_NEG_RESP SA Completed
(optional) ISA_COMMIT =>

2.4 packet.

3. Clear all state and return to IDLE.

4 Security Association Modification

Security Association modification provides the ability to update security
association attributes and parameters within an existing SA without having
to establish a new SA. The use of this exchange can provide performance
benefits without sacrificing the security of the existing communication.
The most common use of this exchange will be to re-
key re-key an existing SA.

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ISAKMP Header ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! SA Syntax Type! Num of Sets ! SA Flags ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SA Attribute Set #1 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SA Attribute Set #2 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SA Attribute Set #N ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

ISA_MODIFY_REQ and ISA_MODIFY_RESP Packet Format

o SA Syntax Type (1 octet) - Defined in Section 2.3.1.

o Num of Sets (1 octet) - Number of Attribute Sets being modified.

o SA Flags (1 octet) - Flags specific to an SA service. Currently
The format for the
SA Flags field ISA_MODIFY packet is set to zero (0) the same as the ISA_INIT_REQ and
ISA_INIT_RESP shown in Figure 4. All fields shown in Figure 4 exist for
the ISA_MODIFY packets.

o SA Attributes (variable) - A list of SA attributes. SA Attributes
field contains only those attributes being updated. SA Attribute
specifications are discussed in section 2.2.1.

4.1 Modification Procedures

The procedure for exchanging information to modify an SA are similiar to
the SA negotiation exchange. The details of SA modification will be de-
scribed in this section as they are solidified during prototype develop-
ment.

2.5

5 Security Association Deletion

During communications it is possible that hosts may be compromised or that
information may be intercepted during transmission. Determining whether
this has occurred is not an easy task and is outside the scope of this
Internet-Draft. However, if it is discovered that transmissions are being
compromised, then it is necessary to delete the current SA and establish a
new SA.

The ISA_DELETE packet provide (shown in Figure 8) provides a controlled method of
informing a peer entity that the initiating entity has deleted an SA(s).
The ISA_DELETE packet provides allows for the deletion of any number of SAs. SAs with
a single message. The receiving en-
tity entity SHOULD clean up its local SA
database. The receiving entity may be us-
ing using the SA for secure communications communi-
cations with more than one party and would not want to actually delete the
SA from it's database, however, its database in this case. However, upon re-
ceipt receipt of an ISA_DELETE
packet the SAs listed in the SPIs field of the packet can not cannot be used with
the initiating entity. The SA Establishment procedure must be repeated invoked to resume
re-establish secure communications.

Figure 8: SA Delete Payload Format

o SPI Count - Number of security associations to be deleted

o Length - length of payload in octets

o SPIs - Initiator's Security Parameter Index(s) to be deleted

5.1 Deletion Procedures

When issuing an ISA_DELETE message: packet, the issuing entity (initiator or re-
sponder) does the following:

1. Create initiator cookie. See Section 1.5.1 2.3.4 for details.

2. Determine SPI of receiving entity.

3. Construct the ISA_DELETE packet.

4. Send Depending on the SA Attributes, apply the agreed upon security
services.

(a) If the SA requires authentication, the ISA_DELETE packet is
processed and the signature placed as noted in Figure 1.

(b) If the SA requires encryption, the ISA_DELETE payload and
Signature are encrypted.

5. Transmit the packet to the destination host as described in Section
2.1.1.

6. Update the local SA database to reflect the SPI deletions.

Upon receipt of an ISA_DELETE message: packet, the receiving entity (initiator or
responder) does the following:

1. Check the ISAKMP header as described in Section 2.1.1.

2. Depending on the SA Attributes, apply the agreed upon security
services in the following order.

(a) If the SA requires encryption, decrypt the ISA_DELETE payload and
Signature. If the decryption fails, the message is discarded and
the following actions are taken:

i. The event is logged in the appropriate system audit file.

ii. Because the ISA_DELETE packet is a unidirectional message a
retransmission will not be performed. The local security
policy will dictate the procedures for continuing. However,
we recommend that the SPIs in the ISA_DELETE packet be checked
to see if the originator was the communicating party. If so,
then these SAs can be deleted from the local SA database. We
also recommend that an ISA_NOTIFY packet with an Error Message
Type (see Section 6) be sent to the originator of the
ISA_DELETE packet. If the SPIs do not match those of the
originator, then no further action should be taken.

(b) If the SA requires authentication, the ISA_DELETE packet is
processed and the calculated signature is compared to the
signature contained in the ISA_DELETE packet. If these signatures
are not identical, the message is discarded and the following
actions are taken:

i. The event is logged in the appropriate system audit file.

3. Unpack the ISA_DELETE payload.

2.6

4. Update the local SA database to reflect the SPI deletions.

6 Notification Message

The ISAKMP ISA_NOTIFY packet contains information one party wants to send
to another. Notification information can be error messages specifying
why a SA could not be established. It can also be status data that a
process managing an SA database, such would be required on a security gateway, database wishes to communicate with a peer process. pro-
cess. For example, a secure front end or security gateway may use the
ISA_NOTIFY message to synchronize SA communication (see Appendix A.2).
The ISA_NOTIFY packet is uni-
directional. unidirectional.

Figure 9: ISA NOTIFY Payload Format

o Notify Message Type (2 octets)

_Notification__Notify_Message_Type_
Error 1
Status 2

o Length (2 octets) - length of payload in octets

o Notify Payload (variable) - Value dependent on the Notify Message
Type

6.1 Notification Procedures

When issuing an ISA_NOTIFY message, the issuing entity (initiator or re-
sponder) does the following:

1. Create initiator cookie. See Section 2.3.4 for details.

2. Determine SPI of receiving entity.

3. Construct ISA_NOTIFY packet.

4. Depending on the SA Attributes, apply the agreed upon security
services.

(a) If the SA requires authentication, the ISA_NOTIFY packet is
processed and the signature placed as noted in Figure 1.

(b) If the SA requires encryption, the ISA_NOTIFY payload and
Signature are encrypted.

5. Transmit the packet to the destination host as described in Section
2.1.1.

Upon receipt of an ISA_NOTIFY message, the receiving entity (initiator or
responder) does the following:

1. Check the ISAKMP header as described in Section 2.1.1.

2. Depending on the SA Attributes, apply the agreed upon security
services in the following order.

(a) If the SA requires encryption, decrypt the ISA_NOTIFY payload and
Signature. If the decryption fails, the message is discarded and
the following actions are taken:

i. The event is logged in the appropriate system audit file.

ii. Because the ISA_NOTIFY packet is a unidirectional message a
retransmission will not be performed. The local security
policy will dictate the procedures for continuing.

(b) If the SA requires authentication, the ISA_NOTIFY packet is
processed and the calculated signature is compared to the
signature contained in the ISA_NOTIFY packet. If these signatures
are not identical, the message is discarded and the following
actions are taken:

i. The event is logged in the appropriate system audit file.

ii. Because the ISA_NOTIFY packet is a unidirectional message a
retransmission will not be performed. The local security
policy will dictate the procedures for continuing.

3. Unpack the ISA_NOTIFY payload.

4. Depending on the Notify Message Type, additional processing may be
necessary.

7 Conclusions

The Internet Security Association and Key Management Protocol (ISAKMP) is
a well designed protocol aimed at the Internet of the future. The massive
growth of the Internet will lead to great diversity in network utiliza-
tion, communications, and security requirements. ISAKMP contains all the
features that will be needed for this dynamic and expanding communications
environment.

ISAKMP's Security Association (SA) feature coupled with authentication
and key establishment provides the security and flexibility that will be
needed to support multiple for future growth and diversity. This security diversity of multi-
ple key ex-
change exchange techniques, encryption algorithms, authentication mechanisms, se-
curity mecha-
nisms, security services, and security attributes. These item may be publicly or
privately defined. attributes will allow users to se-
lect the appropriate security for their network, communications, and secu-
rity needs. The added SA feature allows users to specify and negotiate security
requirements with other users. An additional benefit of supporting multiple multi-
ple techniques in a single protocol is that as new techniques are developed devel-
oped they can easily be added to the pro-
tocol. protocol. This provided provides a path for
the growth of Internet security services. ISAKMP supports both publicly
or privately defined SAs, making it ideal for government, commercial, and
private communications.

ISAKMP provides the ability to establish SAs for multiple security proto-
cols and applications. These protocols and applications may be session-
oriented or sessionless. Having one SA establishment protocol that sup-
ports multiple security protocols eliminates the need for multiple, nearly
identical authentication, key exchange and SA establishment protocols when
more than one security protocol is in use or desired. Just as IP has pro-
vided the common networking layer for the Internet, a common security es-
tablishment protocol is needed if security is to become a reality on the
Internet. ISAKMP provides the common base that allows all other security
protocols to interoperate.

ISAKMP follows good security design principles. It is not coupled to
other insecure transport protocols, therefore it is not vulnerable or
weakened by attacks on other protocols. Also, when more secure transport
protocols are developed, ISAKMP can be easily migrated to them. ISAKMP
also provides protection against protocol related attacks. This protec-
tion provides the assurance that the SAs and keys established are with the
desired party and not with an attacker.

ISAKMP also follows good protocol design principles. Protocol specific
information only is in the protocol header, following the design prin-
ciples of IPv6. The data transported by the protocol is separated into
functional payloads. As the Internet grows and evolves, new payloads to
support new security functionality can be added without modifying the en-
tire protocol.

A Key Exchange ISAKMP Scenarios

Examples

Two key exchanges examples scenerios are are presented to help illustrate the ISAKMP's
ability abil-
ity to support multiple authentication methods and key exchanges.

A.1 Initial ISAKMP Daemon Scenerio

This example steps through two ISAKMP daemons establishing an SA between
themselves. This SA uses DNS Security Extentions [EK94] for authentica-
tion and a Photuris KE

Based on [Karn95] an example of how compliant key exchange. Following the Photuris Key Exchange could be
accomplished in ISAKMP is presented. SA es-
tablishment between the daemons, SAs are established for ESP and AH commu-
nications between user processes.

1. Photuris ``groups'', K-Transform, The initiating daemon sends an ISA_INIT_REQ messages with ISAKMP SA #3,
#2, and S-Transform would be exchanged #1 (in priority order). These SAs are defined in the ISA_INIT packets. C.1.1.

2. The following responding daemon sends an ISA_INIT_RESP message indicating that
ISAKMP SA #2 was selected, which requires DNS Signature and Key
Records and a Photuris fields would be in the ISA_KE packets.

_ISAKMP_Packet__________Value__________
ISA_KE_REQ Initiator-Public-Value
ISA_KE_RESP Responder-Public-Value compliant key exchange [DOW92].

3. The following Photuris fields would be in the ISA_AUTH packets.

_ISAKMP_Packet__________Value___________
ISA_AUTH_REQ Signature [Initiator]
ISA_AUTH_REQ Certificate [Initiator]
ISA_AUTH_RESP Signature [Responder]
ISA_AUTH_RESP Certificate [Resonder] initiating daemon sends an ISA_KE_REQ packet with an index into
well-known table of generator / prime pairs and it's public value.

4. The Upon receipt of ISA_KE_REQ packet the responding daemon computes the
shared secret and session key would be created as described in [Karn95] after each
key exchange payload is received. key.

5. Finally the Transforms, I-Transform The responding daemon sends an ISA_KE_RESP packet with an its public
value and Parameters, R-Transform both the initiator and
Parameters, responders public values signed
using its Private (Signature) Key and Lifetime would be exchanged encrypted in the ISA_NEG packets.

A.2 FORTEZZA Key Exchange Algorithm (KEA)

One of the benefits of ISAKMP is that it is not limited to one session key ex-
change. An example
created.

6. Upon receipt of how ISA_KE_REQ packet the FORTEZZA KEA is accomplished in ISAKMP is
now presented.

1. Options for Encryption algorithm, Authentication Authority initiating daemon computes the
shared secret and session key.

7. The initiating daemon sends an ISA_AUTH_REQ packet with both the
initiator and responders public values signed using its Private
(Signature) Key
Exchange Algorithm would be exchanged and it's DNS name and Public (Verification) Key
signed by it nameserver. All encrypted in the ISA_INIT packets.

2. session key created.

8. The following FORTEZZA fields would be responding daemon sends an ISA_AUTH_RESP packet with it's DNS name
and Public (Verification) signed by it Secure DNS nameserver and
encrypted in the ISA_AUTH&KE packets.

_____Packet_Payload__________________________FORTEZZA_Value_______________________
Authentication Payload Signed Information [Initiator]
Authentication Payload FORTEZZA Certificate [Initiator]
Authentication Payload Signed Information [Responder]
Authentication Payload FORTEZZA Certificate [Resonder]
Key Exchange Payload Message Encryption Key encrypted session key created.

9. The initiating daemon sends an ISA_NEG_REQ packet with ESP SA #2, ESP
SA #1, AH SA #1, and AH SA #2. These SAs are defined in Token Encryption Key
Key Exchange Payload Initiator-Random-Value
Key Exchange Payload Responder-Random-Value

3. C.2.1.

10. The Token Encryption Key is generated.

4. Message Encryption Key is decrypted.

5. Additional Fortezza attributes would responding daemon sends an ISA_NEG_RESP packet indicating that ESP
SA #2, and AH SA #1 was selected.

A.2 Virtual Private Network Scenario

This scenario show how ISAKMP can be exchanged used in a Virtual Public Network
(VPN). The ability to establish SAs for more than just ESP and AH and one
of the ISA_NEG
packets.

Another benefit uses of ISAKMP is that classified key exchanges, such as the
FORTEZZA KEA, can be performed ISA_NOTIFY message are also illustrated.

___________________________Virtual_Public_Network_Scenario_______________________
End System#1 SFE#1 INTERNET SFE#2 End System #2
_______ _______
Establish ES#1 To | | | |
SFE#1 Connection | | | |

SYN | | | |
===> | | | |
| |Establish Connection Between SFEs | |
| | | |
| | SYN | |
| | ===> | |
| | SYN, ACK | |
| | <======= | |
| | ACK | |
| | ===> | |
| | | |
| | Establish SA Between SFEs | |
| | | |
| | ISA_INIT_REQ | |
| | ============> | |
| | ISA_INIT_RESP | |
| | <============ | |
| | ISA_KE&AUTH_REQ | |
| | ==============> | |
| | ISA_KE&AUTH_RESP | |
| | <=============== | |
| | Secure Connection | |Establish SFE#2
| | Between SFEs | |to ES#2 Connection
| | | |
| | | |SYN
| | | |===>
| | | |SYN, ACK
| | | |<=======
| | | |ACK
| | | |===>
| | ISA_NOTIFY(Status == Connected) | |
SYN, ACK | | <==================== | |
<======= | | | |
ACK | | | |
===> | | | |
| | | |
| | Protected Traffic | |
| | ES#1 to ES#2 | |
|_______| <==============> |_______|

The diagram shows an End System (ES) using a public KMP without revealing the
algorithm. This connection oriented proto-
col (we use TCP as an example) establishing a connection with another ES.
Both ES are behind Secure Front Ends (SFE) (e.g. firewalls). The connec-
tion establishment from End System #1 (ES#1) is intercepted by its Secure
Front End (SFE #1). SFE#1 establishes a connection and then a Security
Association (SA), using normal ISAKMP SA establishment procedures, with
SFE #2. Next SFE #2 establishes a connection with ES #2. Upon successful
completion SFE #2 sends an important Department of Defense requirement. SA_NOTIFY with Status equal Connected. SFE #1
completes it's connection with ES #1 and normal end to end communications
takes place secured between SFE #1 and SFE #2. If SFE #2 had been unable
to establish a connection with ES #2 it would have returned an SA_NOTIFY
with Status equal Not Connected with an optional reason code.

B Security Association Attributes

This appendix contains a list of security attributes that should be con-
sidered when defining a Security Association (SA) for a security proto-
col or application. As an example, the security attributes culled from
this list and required for an IP Security (AH, ESP) SA are defined in
[RFC-1825]. The separation of ISAKMP from a specific SA definition is im-
portant to ensure ISAKMP can establish SAs for all possible security func-
tionality. Each security function will be required to maintain a database
of current SAs. This list is based upon an e-mail message [Kent94] to the
IPSEC mail list from Steve Kent and is reproduced here to start a discussion on SA
attributes. Kent.

The authors welcome input on what are meaningful security attributes for
an SA.

The following is a set of possible parameters for each security associ-
ation (SA), e.g., candidate MIB data items where each SA has its own MIB
entry. They may be negotiated or pre-determined, but all are important
for each SA in the most general case.

1. SAID.INBOUND

2. SAID.OUTBOUND

3. ENCAPSULATION

4. INBOUND-CRITERIA

(a) IP-DESTINATION-ADDRESS

(b) IP-SOURCE-ADDRESS

(d) IP-SECURITY-LABEL

(e) TRANSPORT-DESTINATION-PORT

(f) TRANSPORT-SOURCE-PORT

5. PEER-ADDRESS

6. AUTHENTICATION

(a) ENABLED

(b) MECHANISM

o DIGITAL SIGNATURE
i. KEY.INBOUND (Peer's Public Key)

ii. KEY.OUTBOUND (Initator's Private Key)

7. ENCRYPTION

(a) ENABLED

(b) ALGORTIHM

(d) KEY.OUTBOUND

(e) IV.INBOUND

(f) IV.OUTBOUND

8. INTEGRITY

(a) ENABLED

(b) PLAINTEXT

(d) DIRECTION.VALUE

(e) ALGORITHM

(f) KEY.OUTBOUND

(g) KEY.INBOUND

9. COMPRESSION

(a) ENABLED

(b) ALGORITHM

10. REPLAY

(a) ENABLED
(b) SIZE

(d) NUMBER.INBOUND

(e) WINDOW.SIZE

(f) WINDOW

10.

11. FRAGMENTATION

(a) INBOUND

(b) OUTBOUND

11.

12. KEY-MANAGEMENT

(a) NEGOTIATED

(b) TECHNIQUE

(d) REKEY

o GRACE

ii.

o NEXT-SA

iii.

o TIME-BASED

i. ENABLE

ii. TRIGGER

iv.

o TRAFFIC-BASED

i. ENABLE

ii. PACKET-COUNT.INBOUND

iii. PACKET-COUNT.OUTBOUND

D.
iv. TRIGGER.INBOUND

v. TRIGGER.OUTBOUND

C Security Association Examples

C.1 ISAKMP SA Definition

The ISAKMP SA contains the SA attributes that are exchanged in the
ISA_INIT messages.

ISAKMP Security Association
_______________________SA_Attributes_______________________Requirement__
Peer ISAKMP Daemon Address REQUIRED
Security Association Lifetime REQUIRED
Certificate Authority REQUIRED
Digital Signature Algorithm REQUIRED
Signature Key(s) REQUIRED
Security Association Lifetime REQUIRED
Key Establishment Algorithm REQUIRED
Cookie Generation Algorithm REQUIRED
Sensitivity Level (e.g. Secret, Unclassified) RECOMMENDED
Encryption Algorithm RECOMMENDED
Encryption Mode RECOMMENDED
Encryption Transform RECOMMENDED
Encryption Key(s) RECOMMENDED
Key Lifetime or Key Rollover RECOMMENDED
Presence / Absence of cryptographic synchronization or IV RECOMMENDED
Size of cryptographic synchronization or IV RECOMMENDED

C.1.1 ISAKMP SA Examples

ISAKMP SA #1
_________________________SA_Class_________________________________SA_Type_________
Peer ISAKMP Daemon Address N/A
Security Association Lifetime 86400 seconds (1day)
Certificate Authority DMS Root CAW
Certificate Type X.509v1m
Digital Signature Algorithm DSA
Signature Key(s) N/A
Security Association Lifetime 86400 seconds (1day)
Key Establishment Algorithm Fortezza KEA
Cookie Generation Algorithm SHA_1
Sensitivity Level (e.g. Secret, Unclassified) Unclassified
Encryption Algorithm Skipjack
Encryption Mode CDC
Encryption Transform NULL
Encryption Key(s) N/A
Key Lifetime or Key Rollover 3600 seconds (1 hour)
Presence / Absence of cryptographic synchronization or IV Present
Size of cryptographic synchronization or IV 64 bits

ISAKMP SA #2
_________________________SA_Class___________________________________SA_Type__________
Peer ISAKMP Daemon Address N/A
Security Association Lifetime 86400 seconds (1day)
Certificate Authority DNSSEC janeway.ncsc.mil
Certificate Type RR
Digital Signature Algorithm RSA
Signature Key(s) N/A
Security Association Lifetime 86400 seconds (1day)
Key Establishment Algorithm X9.42_STS
Cookie Generation Algorithm MD5
Sensitivity Level (e.g. Secret, Unclassified) N/A
Encryption Algorithm DES
Encryption Mode CDC
Encryption Transform RFC-1829
Encryption Key(s) N/A
Key Lifetime or Key Rollover 600 seconds (10 minutes)
Presence / Absence of cryptographic synchronization or IV Present
Size of cryptographic synchronization or IV 64 bits
ISAKMP SA #3
_________________________SA_Class___________________________________SA_Type__________
Peer ISAKMP Daemon Address N/A
Security Association Lifetime 86400 seconds (1day)
Certificate Authority IPRA PCA UNINETT
Certificate Type X.509v1
Digital Signature Algorithm RSA
Signature Key(s) N/A
Security Association Lifetime 86400 seconds (1day)
Key Establishment Algorithm STS
Cookie Generation Algorithm MD5
Sensitivity Level (e.g. Secret, Unclassified) N/A
Encryption Algorithm DES
Encryption Mode CDC
Encryption Transform RFC-1829
Encryption Key(s) N/A
Key Lifetime or Key Rollover 600 seconds (10 minutes)
Presence / Absence of cryptographic synchronization or IV Present
Size of cryptographic synchronization or IV 64 bits

C.2 ESP SA and AH SA Definitions

The following SAs are defined in [RFC-1825] and are presented here for
comparative and completeness purposes.

AH Security Association
__________________SA_Attributes__________________Requirement_
Authentication Algorithm REQUIRED
Authentication Mode REQUIRED
Authentication Key(s) REQUIRED
Key Lifetime or Key Rollover RECOMMENDED
Security Association Lifetime RECOMMENDED
Sensitivity Level (e.g. Secret, Unclassified) RECOMMENDED
ESP Security Association
_______________________SA_Attributes_______________________Requirement__
Encryption Algorithm REQUIRED
Encryption Mode REQUIRED
Encryption Transform REQUIRED
Encryption Key(s) REQUIRED
Presence / Absence of cryptographic synchronization or IV REQUIRED
Size of cryptographic synchronization or IV REQUIRED
Authentication Algorithm RECOMMENDED
Authentication Mode RECOMMENDED
Authentication Key(s) RECOMMENDED
Key Lifetime or Key Rollover RECOMMENDED
Security Association Lifetime RECOMMENDED
Sensitivity Level (e.g. Secret, Unclassified) RECOMMENDED

C.2.1 ESP and AH SA Examples

AH SA #1
____________________SA_Class_____________________________SA_Type__________

Authentication Algorithm MD5
Authentication Mode Keyed
Authentication Key(s) Photuris
Key Lifetime or Key Rollover 600 seconds (10 minutes)
Security Association Lifetime 3600 seconds (1 hour)
Sensitivity Level (e.g. Secret, Unclassified) N/A

AH SA #2
____________________SA_Class_____________________________SA_Type__________
Authentication Algorithm SHA
Authentication Mode NULL
Authentication Key(s) NULL
Key Lifetime or Key Rollover 600 seconds (10 minutes)
Security Association Lifetime 3600 seconds (1 hour)
Sensitivity Level (e.g. Secret, Unclassified) N/A
ESP SA #1
_________________________SA_Class___________________________________SA_Type__________
Encryption Algorithm DES
Encryption Mode CBC
Encryption Transform RFC-1829
Encryption Key(s) Phutoris Generated
Presence / Absence of cryptographic synchronization or IV Present
Size of cryptographic synchronization or IV 64 bits
Authentication Algorithm NULL
Authentication Mode NULL
Authentication Key(s) NULL
Key Lifetime or Key Rollover 600 seconds (10 minutes)
Security Association Lifetime 3600 seconds (1 hour)
Sensitivity Level (e.g. Secret, Unclassified) N/A

ESP SA #2
_________________________SA_Class___________________________________SA_Type__________
Encryption Algorithm DES
Encryption Mode CBC
Encryption Transform RFC-1829
Encryption Key(s) X9.42_DH Generated
Presence / Absence of cryptographic synchronization or IV Present
Size of cryptographic synchronization or IV 64 bits
Authentication Algorithm NULL
Authentication Mode NULL
Authentication Key(s) NULL
Key Lifetime or Key Rollover 600 seconds (10 minutes)
Security Association Lifetime 3600 seconds (1 hour)
Sensitivity Level (e.g. Secret, Unclassified) N/A

C.2.2 Fortezza SA Examples

Fortezza AH SA
____________________SA_Class___________________________SA_Type________
Authentication Algorithm SHA
Authentication Mode NULL
Authentication Key(s) DMS Root CAW
Key Lifetime or Key Rollover 86400 seconds (1day)
Security Association Lifetime 86400 seconds (1day)
Sensitivity Level (e.g. Secret, Unclassified) N/A
Fortezza ESP SA
_________________________SA_Class__________________________________SA_Type_________
Encryption Algorithm Skipjack
Encryption Mode CBC
Encryption Transform NULL
Encryption Key(s) Fortezza KEA Generated
Presence / Absence of cryptographic synchronization or IV Present
Size of cryptographic synchronization or IV 64 bits
Authentication Algorithm DSA
Authentication Mode NULL
Authentication Key(s) DMS Root CAW
Key Lifetime or Key Rollover 3600 seconds (1 hour)
Security Association Lifetime 86400 seconds (1day)
Sensitivity Level (e.g. Secret, Unclassified) Unclassified
Security Considerations

Cryptographic analysis techniques are improving at a steady pace. The
continuing improvement in processing power makes once computational pro-
hibitive cryptographic attacks more realistic. New cryptographic algo-
rithms and public key generation techniques are also being developed at a
steady pace. New security services and mechanisms are being developed at
an accelerated pace. A consistent method of choosing from a variety of
security services and mechanisms and to exchange attributes required by
the mechanisms is important to security in the complex structure of the
Internet. However a system that locks itself into a single cryptographic
algorithm, key exchange technique, or security mechanism will become in-
creasingly vulnerable as time passes.

UDP is an unreliable datagram protocol and therefore its use in ISAKMP in-
troduces a number of security considerations. Since UDP is unreliable,
but a key management protocol must be reliable, the reliability is built
into ISAKMP. While ISAKMP utilizes UDP as its transport mechanism, it
doesn't soley rely on any UDP information (e.g. checksum, length) for its
processing.

Another issue that must be considered in the development of IKMP is the
effect of firewalls on the protocol. Many firewalls filter out all UDP
packets, making reliance on UDP questionable in certian environments.

A number of very important security considerations are presented in
[Atki95].
[RFC-1825]. One bares repeating. Once a private session key is created
it must be safely stored. Failure to properly protect the private key
from access both internal and external to the system completely nullifies
any protect provided by the IP Security services.

Acknowledgements

Marsha Gross, Bill Kutz, Mike Oehler, Mark Schneider, and Pete Sell provided signifi-
cant pro-
vided significant input and review to this document.

Thanks to Carl Muckenhirn of SPARTA, Inc. for his assistance with LaTeX.

References

[ANSI94] ANSI, X9.42: Public Key Cryptography Using Irreversible
Algorithms for the Financial Services
Industry -- Management Establishment of Symmetric Algorithm Keys Using
Diffie-Hellman, Working Draft, September, 1994.

[Atki95] Randell Atkinson, Security Architecture for the Internet
Protocol, October 26, 1995.

[DOW92] W. Diffie, M.Wiener, P. Van Oorschot, Authtication and
Authenticated Key Exchanges, Designs, Codes, and Cryptography, 2,
107-125, Kluwer Academic Publishers, 1992.

[Berg] Berge, N.H., UNINETT PCA Policy Statements, Internet-Draft, working work
in progress, 8 May, November, 1995.

[EK94] Eastlake III, D. and c. C. Kaufman, Domain Name System Protocol Secu-
rity
Security Extensions, Internet-Draft, working work in progress, March, 1994. Oct, 1995.

[Karn95] Karn P. and B. Simpson, The Photuris Key Management Protocol,
Internet-Draft, working work in progress, March, November, 1995.

[Kent94] Steve Kent, IPSEC SMIB, e-mail to ipsec@ans.net, August 10,
1994.

[RFC-1155] Rose M. and K. McCloghrie, Structure and Identification of
Management Information for TCP/IP-based Internets, RFC-1155, May,
1990.

[RFC-1212] McCloghrie K. and M. Rose, Concise MIB Definitions, RFC-1212,
March 26, 1991.

[RFC-1213] McCloghrie K. and M. Rose, Management Information Base for
Network Management of TCP/IP-based Internets: MIB-II, RFC-1213,
March 26, 1991.

[RFC-1422] Steve Kent, Privacy Enhancement for Internet Electronic Mail:
Part II: Certificate-Based Key Management, RFC-1422, February 1993.

[RFC-1825] Randell Atkinson, Security Architecture for the Internet
Protocol, RFC-1825, August, 1995.

[Secu] SECUREWARE INC., Peer Authentication and Key Management Protocol
Specification, Version 2.2, October 27, 1995.

[Schn94] Bruce Schneier, Applied Cryptography - Protocols, Algorithms,
and Source Code in C, John Wiley & Sons, Inc., 1994.

[Spar94a] Harney H., C. Muckenhirn, and T. Rivers, Group Key Management
(GKMP) Architecture, SPARTA, Inc., Internet-Draft, September, 1994.

[Spar94b] Harney H., C. Muckenhirn, and T. Rivers, Group Key Management
(GKMP) Specification, SPARTA, Inc., Internet-Draft, September, 1994.

Addresses of Authors

The three two authors are with:

National Security Agency
ATTN: R2 R23
9800 Savage Road
Ft. Meade, MD. 20755-6000

Douglas Maughan
Phone: 301-688-0847
E-mail:wdmaugh@tycho.ncsc.mil

Barbara Patrick
Phone: 301-688-0298
E-mail:bspatri@orion.ncsc.mil

Mark Schertler
Phone: 301-688-0849
E-mail:mjs@tycho.ncsc.mil