wdiff draft-ietf-ipsec-isakmp-03.txt draft-ietf-ipsec-isakmp-04.txt

IPSEC Working Group Douglas Maughan, Mark Schertler
INTERNET-DRAFT National Security Agency
draft-ietf-ipsec-isakmp-03.txt,
draft-ietf-ipsec-isakmp-04.txt, .ps November February 21, 1995 1996

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
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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 5
1.1 Authentication . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1.1Certificate Authorities . . . . . . . . . . . . . . . . . . . 6
1.1.2Entity Naming . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1.3ISAKMP Requirements . . . . . . . . . . . . . . . . . . . . . 7
1.2 Security Associations and Management . . . . . . . . . . . . . . 8
1.2.1Security Associations and Registration . . . . . . . . . . . . 8
1.2.2ISAKMP Requirements . . . . . . . . . . . . . . . . . . . . . 8 9
1.3 Public Key Cryptography . . . . . . . . . . . . . . . . . . . . . 9
1.3.1Key Exchange Properties . . . . . . . . . . . . . . . . . . . 9
1.3.2ISAKMP Requirements . . . . . . . . . . . . . . . . . . . . . 11
1.4 ISAKMP Protection . . . . . . . . . . . . . . . . . . . . . . . . 11
1.4.1Anti-Clogging (Denial of Service) . . . . . . . . . . . . . . 11
1.4.2Connection Hijacking . . . . . . . . . . . . . . . . . . . . . 11
1.4.3Man-in-the-Middle Attacks . . . . . . . . . . . . . . . . . . 11 12
1.5 Multicast Communications . . . . . . . . . . . . . . . . . . . . 12

2 Description of the Protocol 12 13
2.1 ISAKMP Header Format Architecture . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.1General Message Processing
2.2 ISAKMP Packet Exchanges . . . . . . . . . . . . . . . . . . 15
2.2 ISAKMP Packet Exchanges . . . 14
2.2.1Base Exchange . . . . . . . . . . . . . . . . . . 17
2.2.1Base . . . . . . 14
2.2.2Identity Protection Exchange . . . . . . . . . . . . . . . . . 14
2.2.3Authentication Only Exchange . . . . . . . 17
2.2.2Identity Protection Exchange . . . . . . . . . . 15
2.3 ISAKMP Details . . . . . . . 17
2.2.3Authentication Only Exchange . . . . . . . . . . . . . . . . . 18
2.3 . 16
2.3.1Basic ISAKMP Details Concepts . . . . . . . . . . . . . . . . . . . . 16
2.3.2ISAKMP Header Format . . . . . 19
2.3.1Security Association Attributes . . . . . . . . . . . . . . . 19
2.3.2Transport Protocol . 17
2.3.3SPI Usage . . . . . . . . . . . . . . . . . . . . . 21
2.3.3RESERVED Fields . . . . . 20
2.3.4General Message Processing . . . . . . . . . . . . . . . . . . 21
2.3.4Anti-Clogging Token (``Cookie'') Creation
2.3.5Transport Protocol . . . . . . . . . . 21
2.3.5SA Flags Field . . . . . . . . . . . . 23
2.3.6RESERVED Fields . . . . . . . . . . . . 22 . . . . . . . . . . . 23
2.3.7Anti-Clogging Token (``Cookie'') Creation . . . . . . . . . . 23
3 Security Association Establishment 22 25
3.1 Security Association Initialization . . . . . . . . . . . . . . . 22 25
3.1.1SA Initialization Procedures . . . . . . . . . . . . . . . . . 24 26
3.2 Authentication and Key Exchange . . . . . . . . . . . . . . . . . 25 28
3.2.1Authentication Payload Format . . . . . . . . . . . . . . . . 26 28
3.2.2Key Exchange Payload Format . . . . . . . . . . . . . . . . . 28 29
3.2.3Authentication and Key Exchange Procedures . . . . . . . . . . 29 30
3.3 Security Association Negotiation . . . . . . . . . . . . . . . . 30 32
3.3.1SA Negotiation Procedures . . . . . . . . . . . . . . . . . . 31
3.4 SA Negotiation Conclusion 32

4 Security Association Modification 38
4.1 Modification Procedures . . . . . . . . . . . . . . . . . . . . 34
3.4.1SA Negotiation Conclusion . 38
5 Security Association Deletion 38
5.1 Deletion Procedures . . . . . . . . . . . . . 34

4 Security Association Modification 36
4.1 Modification Procedures . . . . . . . . . . 39

6 Notification Message 41
6.1 Notify Message Types . . . . . . . . . . . 36
5 Security Association Deletion 36
5.1 Deletion Procedures . . . . . . . . . . . 42
6.2 Notification Procedures . . . . . . . . . . . . 37

6 Notification Message 39
6.1 Notification Procedures . . . . . . . . . 42

7 Conclusions 44

A IP Security DOI 45
A.1 IP Security Proposal Formats . . . . . . . . . . . . 40

7 Conclusions 41

A ISAKMP Scenarios 43
A.1 Initial ISAKMP Daemon Scenerio . . . . . . 45
A.2 ESP SA and AH SA Proposals . . . . . . . . . . . 43
A.2 Virtual Private Network Scenario . . . . . . . . 48
A.3 Oakley Proposal . . . . . . . . 44
B Security Association Attributes 47

C Security Association Examples 51
C.1 ISAKMP SA Definition . . . . . . . . . . . . . . . . . 51
A.4 Attribute Class Assigned Numbers . . . . . 51
C.1.1ISAKMP SA Examples . . . . . . . . . . . 53
A.5 Attribute Value Assigned Numbers . . . . . . . . . . . 52
C.2 ESP SA and AH SA Definitions . . . . . 54
A.5.1Sensitivity Level Assigned Numbers . . . . . . . . . . . . . 53
C.2.1ESP and AH SA Examples . 54
A.5.2Key Exchange Identifiers (KEI) Assigned Numbers . . . . . . . 54
A.5.3Encryption Transform Assigned Numbers . . . . . . . . . . . . 54
C.2.2Fortezza SA Examples
B ISAKMP Scenarios 55
B.1 Oakley Scenario . . . . . . . . . . . . . . . . . . . . . . . . . 55
B.2 Virtual Private Network Scenario . . . . . . . . . . . . . . . . 57

C Security Association Attributes 60
1 Introduction

This document describes an Internet Security Association and Key Manage-
ment Protocol (ISAKMP). ISAKMP combines the security concepts of authen-
tication, key management, and security associations to establish the re-
quired security for government, commercial, and private communications on
the Internet. ISAKMP 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 bound to any specific cryptographic algorithm, key gener-
ation technique, or security mechanism. This flexibility is beneficial
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 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 /
reflection, man-in-the-middle, and connection hijacking attacks. This is
important because these are the types of attacks that are targeted against
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 au-
thentication of the entity at the other end of the communication. Many
authentication mechanisms are available. Authentication mechanisms fall
into two catagories of strength - weak and strong. Passwords are an exam-
ple of 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, such as the Digital Signature Standard (DSS) and the
Rivest-Shamir-Adleman (RSA) signature, are public key based strong authen-
tication mechanisms. When using digital signatures each entity requires a
public and a private key. Certificates are an essential part of a digital
signature authentication mechanism. Certificates bind a specific enti-
ties identity (be it host, network, user, or application) to its public
keys and possibly other security-related information such as privileges,
clearances, and 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]. [Schneier].

1.1.1 Certificate Authorities

Certificates require an infrastructure for generation, verification, man-
agement and distribution. The Internet Policy Registration Authority
(IPRA) [RFC-1422] has been established to direct this infrastructure for
the IETF. The IPRA certifies Policy Certification Authorities (PCA). PCAs
control Certificate Authorities (CA) which certify users and subordinate subordi-
nate entities. Current certificate related work includes the Domain Name Sys-
tem
System (DNS) Security Extensions [EK94] [DNSSEC] which will provide signed entity en-
tity keys in the DNS. The Public Key Infrastucture (PKIX) working group
is speci-
fying specifying an Internet profile for X.509 certificates. There is also
work go-
ing going 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 in-
frastructure for the U.S. Government. Alternatively, if no infrastructure
exists, the PGP Web of Trust certificates can be used to provide user authentica-
tion au-
thentication 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] [Berge] 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?). e-mail. Another web of trust 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 mandate a specific mechanism. signature algo-
rithm or certificate authority (CA). ISAKMP allows an entity initiating
communications to indicate which signature al-
gorithms CAs it supports. After selection of a common algorithm,
CA, 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 au-
thentication exchange. The protocol provides a facility for identification identifica-
tion of different cer-
tificate certificate authorities, certificate types (e.g. X.509v1 certificates, X.509,
PKCS
#7), #7, PGP, DNS SIG and KEY records), and the exchange of the certificates certifi-
cates 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 trusted third
party called a key distribution center (KDC) to distribute secret session
keys. An example is Kerberos, where the trusted third party is the Ker-
beros server, which holds secret keys for all clients and 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 defined by the TTP and directory service themselves
and are outside the scope of this specification.

1.2 Security Associations and Management

A Security Association (SA) is a relationship between two or more entities
that describes how the entities will utilize security services to 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 in-
stantiation of the existing relationship. The existence of this relation-
ship, represented by the information, is what provides the agreed upon se-
curity information needed by entities to securely interoperate. All enti-
ties must adhere to the SA for secure communications to be possible. When
accessing SA attributes, entities use a pointer or identifier refered to
as the Security Parameter Index (SPI). See [RFC-1825] for details on IP
Security SAs and SPIs definitions.

1.2.1 Security Associations and Registration

The 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 mechanism, cryptographic
algorithm, algorithm mode, key length, and Initialization Vector (IV).
Other protocols that provide algorithm and mechanism independent security
MUST define their SA attributes requirements. The separation of ISAKMP
from a specific SA definition is important to ensure ISAKMP can establish
SAs for all possible security protocols and applications.

NOTE: See Appendix B C for a discussion of SA attributes that should be con-
sidered when defining a security protocol or application.

In 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 Assigned Numbers Authority
(IANA) provides this function for the Internet.

1.2.2 ISAKMP Requirements

Security Association (SA) establishment MUST be part of the key manage-
ment protocol defined for IP based networks. The SA concept is required
to support security protocols in a diverse and dynamic networking envi-
ronment. Just as authentication and key exchange must be linked to pro-
vide assurance that the key is established with the authenticated party
[DOW92], SA establishment must be linked with the authentication and the
key exchange protocol.

ISAKMP provides the protocol exchanges to establish a security association
between entities. First, an initial protocol exchange allows a basic set
of security attributes to be agreed upon. This basic set provides protec-
tion for subsequent ISAKMP exchanges. It also indicates the authentica-
tion method and key exchange that will be performed as part of the ISAKMP
protocol. If a basic set of security attributes is already in place on
the communicating entities the initial ISAKMP exchange may be skipped and
the key and authentication exchanges issued directly. After the basic set
of security attributes has been agreed upon, initial identity authenti-
cated, and required keys generated, another security attribute exchange
takes place to establish the complete SA which will be used for subsequent
communications by the entity that invoked ISAKMP. The basic set of SA at-
tributes that MUST be implemented to provide ISAKMP interoperability are
defined in Appendix C. A. *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, scalable, and efficient way
for users to obtain the shared secrets and session keys 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]). [ANSI]). 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
of using public key cryptography for key establishment are key transport
and key generation. An example of key transport is the use of the RSA al-
gorithm to encrypt a randomly generated session key (for encrypting subse-
quent communications) with the recipient's public key. The encrypted ran-
dom key is then sent to the 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 il-
lustrates key generation using public key cryptography. The D-H algorithm
is begun by two users exchanging public information. Each user then mathe-
matically math-
ematically combines the other's public information along with their own se-
cret
secret information to compute a shared secret value. This secret value
can be used as a session key or as a key encryption key for encrypting
a ran-
domly randomly generated session key. This method generates a session key
based on public and secret information held by both users. The benefit
of the D-H algorithm is that the key used for encrypting messages is based
on infor-
mation information held by both users. Assuming checks for weak values neither nei-
ther party can force the session key to a predetermined value. Detailed descrip-
tions
descriptions of these algorithms can be found in [Schn94]. [Schneier]. There are a
number of variations on these two key generation schemes and these variations varia-
tions do not necessarily interoperate.

Key Exchange Authentication Key exchanges may be authenticated during the
protocol or after protocol completion. Authentication of the key exchange
during the protocol is provide provided when each party provides proof it has the
secret session key before the end of the protocol. Proof can be provided
by encrypting known data in the secret session key during the protocol ex-
change. Authentication after the protocol must occur in subsequent commu-
nications. Authentication during the protocol is preferred so subsequent
communications are not initiated if the secret session key is not estab-
lished with the desired party.

Key Exchange Symmetry A key exchange provides symmetry if either party can
initiate the exchange and 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 Perfect forward secrecy
is provided by a key exchange protocol if disclosure of long-term cryp-
tographic keying material (e.g. public signature keys) does not compro-
mise previously generated keys. Back traffic protection is provided by
the independent generation of each key such that subsequent keys are not
dependent on any previous key. There is a subtle difference. Past ses-
sion keys will NOT be obtainable is if the long-term key is compromised in
perfect forward secrecy; Past session keys will NOT be obtainable if the
current session key is compromised in back traffic 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 protec-
tion of communications are destroyed after use and not kept for any rea-
son.

1.3.2 ISAKMP Requirements

An authenticate key exchange MUST be supported by ISAKMP. Users SHOULD
choose additional key establishment algorithms based on 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, back traffic protection, computational overhead, key escrow, and
key strength. Based on user requirements, ISAKMP allows an entity initi-
ating communications to indicate which key exchanges it supports. After
selection of a key exchange, the protocol provides the messages required
to support the actual key 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] [Karn] 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], [Karn], an exchange prior to
CPU-intensive public key operations can thwart some denial of service
attempts at-
tempts (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.

1.4.2 Connection Hijacking

ISAKMP prevents connection hijacking by linking the authentication, key
exchange and security association exchanges. This linking prevent prevents an at-
tacker
attacker from allowing the authentication to complete and then jumping
in and impersonating one entity to the other during the key and security as-
sociation
association 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 sender, re-
playing old messages and redirecting messages. ISAKMP features prevent
these types of attacks from being successful. The linking of the ISAKMP
exchanges prevents the insertion of messages in the protocol exchange.
The ISAKMP protocol state machine is defined so deleted messages will not
cause a partial SA to be created, the state machine will clear all state
and return to idle. The state machine also prevents reflection of a mes-
sage from causing harm. The requirement for a new cookie with time vari-
ant material for each new SA establishment prevents attacks that involve
replaying old messages. The ISAKMP strong authentication requirement pre-
vents an SA 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 will not be established. The ISAKMP specifica-
tion defines where abnormal processing has occurred and recommends notify-
ing the 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 man-
agement protocol from the unicast point of view. It is expected that mul-
ticast communications will require the same security services as unicast
communications and may introduce the need for additional security ser-
vices. The issues of distributing SPIs for multicast traffic are pre-
sented in [RFC-1825]. Multicast security issues are also discussed in
[BC]. Upon agreement and implementation of a security association protocol pro-
tocol for the Internet unicast environment, we fully intend to examine any
additional security requirements for multicast communica-
tions. communications. For an introduction in-
troduction to the issues related to multicast security consult the Internet Inter-
net 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, negotiate, modify and
delete Security Associations (SA). SAs contain all the information re-
quired for execution of IP security services, such as the IP Authentica-
tion Header (AH), the IP Encapsulating Security Payload (ESP), and routing
protocol authentication mechanisms. ISAKMP includes packet 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 au-
thentication mechanism.

2.1 ISAKMP Architecture

The following figure is a high level view of the placement of ISAKMP in a
network architecture.

+-------------+ +--------------+
! Negotiation ! Situation ! Application !
! Server !<---- ! Process !
+-------------+ ! +--------------+
! ISAKMP ! ! ! Appl Protocol!
+-------------+ ! SPI +--------------+
! v !
+---------------------------------------------+
! Sockets !
+---------------------------------------------+
! Transport Protocol (TCP / UDP) !
+---------------------------------------------+
! IP !
+---------------------------------------------+
! Link Layer Protocol !
+---------------------------------------------+

Figure 1: ISAKMP Relationships

The negotiation server is an application process which interfaces with the
different policy databases (security, network access, cryptographic, au-
thentication, etc.) that a system may require. It calls upon ISAKMP to
deliver the data required to establish an SA and key and authenticate the
exchange. The negotiation server can be invoked manually by a user or au-
tomatically by an up-call from a security protocol when it requires an SA.

The situation contains the identification and credential information re-
quired by the negotiation server to make policy decisions. The negotia-
tion server returns a SPI when an SA is established.

2.2 ISAKMP 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 ba-
sic notes describing what has happened after each packet exchange. These
exchanges are a high level summary of the packet flow, they do not show
processing or error handling. Detailed connection establishment process-
ing is defined in sections 3 through 6.

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

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

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.

Authentication Only 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

2.3 ISAKMP Details

The following sections contain the details of ISAKMP. Sections 2.1 2.3.1
through
2.3 2.3.7 cover details that are pertinent to the entire protocol.
Sections 3 through 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

2.3.1 Basic ISAKMP Concepts

Domain of Interpretation The Domain of Interpretation (DOI) identifier is
used to interpret the payloads of ISAKMP payloads. The concept of a DOI
is based on previous work by the IETF CIPSO Working Group, but extended
beyond security label interpretation to include naming and interpretation
of security services. The DOI defines:

o The set of information that will be used to determine the required
security services (this information is called a situation).

o The set of security policies that must be supported.

o Syntax rules for the specification of proposed security services. A
set of security services is called a protection suite.

o A common scheme for identifying cryptographic mechansisms, including
encryption algorithms, key exchange algorithms, and certificate
authorities.

o A naming scheme for the cryptographic algorithms supported within the
domain, and for common Key Exchange Identifiers.

Specifications of the rules for individual DOIs will be presented in sep-
arate documents. The rules for the Internet Security DOI is contained in
Appendix A.

A system may support multiple Domains of Interpretation. All systems MUST
support the Internet Security DOI.

Situation A situation contains all of the security-relevant information
that a system considers necessary to decide the security services required
to protect the session being negotiated. For example, in the Internet
Security DOI (see Appendix A), the situation consists of only the address
of the peer being contacted. In other DOIs, the situation may include
security classifications, modes of operation (normal vs. emergency), etc.

Protection Suite A protection suite is a list of the security services
that must be applied at various security protocols. For example, a pro-
tection suite may consist of DES encryption in IP ESP, and keyed MD5 in
IP AH. All of the protections in a suite must be treated as a single unit.
This is because security services in different security protocols can have
subtle interactions, and the effects of a suite must be analyzed and veri-
fied as a whole.

Proposal A proposal is a list, in decreasing order of preference, of the
protection suites that a system considers acceptable to protect traffic
under a given situation.

2.3.2 ISAKMP Header Format

ISAKMP has a fixed header format (shown in Figure 1) 2) followed by a vari-
able length payload, optional digital signature, and optional padding. A
fixed header simplifies parsing, providing the benefit of protocol parsing
software that is less complex and easier to implement. The fixed header
contains the information required by the protocol to maintain state, pro-
cess payloads and prevent attacks (e.g. denial of service and replay).
Based on the message type, each header is followed by a payload specific
to the message type. The payload for each message is defined in sections
3 through 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 ! Exch ! Vers ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Security Parameter Index (SPI) !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Initiator-Cookie ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Responder-Cookie ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Message Type !
~ Payload ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Exch !
~ Digital Signature ~ Vers ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Security Parameter Index (SPI) !
~ Padding ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Auxillary (SPI) !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: 2: ISAKMP Header Format

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

__ISAKMP_Message__Message_Type_

__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
ISA_NEW_GROUP_REQ 15
ISA_NEW_GROUP_RESP 16
IANA Use 16-127 17-127
Future Use 128-255

o Exchange (4 bits) - indicates the type of exchange, see 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 use
of the SPI field is described in Section 2.3.3

o Auxillary SPI (4 octets) - The use of the initiator expects to receive Auxiliary SPI field is
described in
all subsequent packets. 2.3.3

o Initiator Cookie (16 (8 octets) - Cookie of entity that initiated SA
establishment, SA modify or SA delete.

o Responder Cookie (16 (8 octets) - Cookie of entity that is responding to
an SA establishment, SA modify or SA delete request.

o Payload (variable) -

2.3.3 SPI Usage

While bootstrapping secure channels between systems, ISAKMP cannot assume
the existence of security services, and must provide some protections for
itself. Therefore, ISAKMP distinguishes two different types of SPIs. The format
first type of SPI, called a negotiation SPI, refers to a ``local'' secu-
rity association, implemented by the payload ISAKMP service itself. The second
type is based on called a protection SPI, and is used to refer to the
message type. These are defined in sections 3 through 6.

o Signature - The digital signature SA being de-
veloped on behalf of the initiator other security protocols. Negotiation SPIs are mean-
ingless outside of the ISAKMP
message. This field negotiation server, while protection SPIs will not be included on all packets
used by protocols such as AH and will ESP.

Although SPIs are classified two different ways, all SPIs must be
determined by selected
from the negotiated same SPI-space, so that the ISAKMP service can uniquely identify
an SA attributes.

o Padding - This based on a SPI.

In general, the SPI field in the ISAKMP header contains the receiving en-
tity's negotiation SPI. The only exception to this is an optional the ISA_INIT_REQUEST
message, because the receiver has not yet established a reciving SPI for
the session. In the ISA_INIT_REQUEST message, the the SPI field contains
the SPI that may the sender will be added depending using for the session.

The Auxiliary SPI field is necessary because ISAKMP needs both a handle on
the type internal ``negotiation SA'', in order to protect or unprotect messages
from ISAKMP peers, as well as a handle for the protection SA that is being
developed.

The following table describes the contents of encryption algorithm. If the encryption mechanism two SPI fields for each
of the message types:

__ISAKMP_Message_______SPI_____Auxiliary_SPI__
ISA_INIT_REQ REQ NEG SPI 0
ISA_INIT_RESP REQ NEG SPI REC NEG SPI
ISA_KE_REQ REC NEG SPI REQ SPI
ISA_KE_RESP REQ NEG SPI REC SPI
ISA_AUTH_REQ REC NEG SPI REQ NEG SPI
ISA_AUTH_RESP REQ NEG SPI REC NEG SPI
ISA_AUTH&KE_REQ REC NEG SPI REQ NEG SPI
ISA_AUTH&KE_RESP REQ NEG SPI REC NEG SPI
ISA_NEG_REQ REC NEG SPI REQ PROT SPI
ISA_NEG_RESP REC NEG SPI REC PROT SPI
ISA_MODIFY_REQ REC NEG SPI REC SPI
ISA_MODIFY_RESP REQ NEG SPI REQ SPI
ISA_NOTIFY REC NEG SPI REC SPI
ISA_DELETE REQ NEG SPI REQ SPI
ISA_NEW_GROUP_REQ REC NEG SPI 0
ISA_NEW_GROUP_RESPREQ NEG SPI 0

Notes:

REQ NEG SPI = Requestor's negotiation SPI
REC NEG SPI = Receiver's negotiation SPI
REQ PROT SPI = Requestor's protection SPI
REC PROT SPI = Receiver's protection SPI
REQ SPI = Requestor's SPI (either negotiation or protection)
REC SPI = Receiver's SPI (either negotiation or protection)

For KE messages: if the messages are establishing keys for a negotiation
session, the SPI is
based on block encryption, then this field may be necessary to ensure a negotiation SPI. Otherwise, the packet Auxiliary SPI is a specific size.

2.1.1
protection SPI.

For MODIFY, NOTIFY, and DELETE messages: the Auxiliary SPI can refer to
either type of SPI.

2.3.4 General Message Processing

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

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

1. Sets a timer and initializes a retry counter.

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

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

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

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

1. 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 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 the Message Type field to confirm it is valid. If the Message
Type field validation fails, the message is discarded and the
following actions are 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 the Exchange field to confirm it is valid for the Message Type
requested. If the Exchange field validation fails, the message is
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 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 the SPI validation fails, the message is
discarded and the 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 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 transmitting
entity (message originator). The procedures for sending these
responses are also outline in sections 3 through 6.

2.2 ISAKMP Packet Exchanges

2.2.1 Base Exchange

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

2.2.3 Authentication Only Exchange

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 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 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 be supported by

2.3.5 Transport Protocol

ISAKMP 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 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. 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.

Figure 2 depicts the syntax for exchanging security attributes 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 ! 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 (2 octets) - Security service proposed set supports.
Examples are IP AH, IP ESP, and OSPF authentication

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

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

o Attribute Type (2 octets) - examples of attribute 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 Attribute
Classes * 4 octets). Computing the size of a particular set allows the
determination of the beginning of the next set without completely parsing
the current set. This is necessary when it is determined that the current
set is not 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 precedence. Specifically, the first attribute type is the
highest priority type, followed by other choices. Each subsequent choice
is listed in descending priority order. An attribute type must be chosen
for each attribute class to establish a complete SA.

Figure 3 shows the syntax for the optional list exchange format. The num-
ber of types is determined 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 Attribute Types for the given Attribute
Class

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

Appendix B presents an outline containing a comprehensive listing of SA
attributes. This listing of attributes are initial definitions and are
presented to stimulate thought and discussion on SAs. The final SA for
a protocol SHOULD can be defined in that implemented over any transport 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. For example, Appendix C
describes the sample security associations for ISAKMP and IPSP ESP and AH.

2.3.2 Transport Protocol IP itself. The
User Datagram Protocol (UDP) is the transport protocol minimum requirement for ISAKMP. UDP
checksumming discards UDP packets with an incorrect or zero (0) checksum. interoperability.
The ISAKMP well-known port is unaware of the discard, but will resend the packet when its re-
send timer expires.

2.3.3 TBD.

2.3.6 RESERVED Fields

The existence of RESERVED fields are strictly used to preserve byte
alignement. align-
ment. 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.

2.3.4

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

Phil Karn's Internet Draft [Karn95] [Karn] states that cookie generation is im-
plementation imple-
mentation 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, 3.1 to 3.3, describe the three basic phases that com-
prise SA Establishment: SA Initialization, Key and Authentication infor-
mation exchange, and SA Negotiation.

3.1 Security Association Initialization

The initialization exchange of SA establishment is composed of the
ISA_INIT_REQ and ISA_INIT_RESP packets shown in figure 4. 3. The ISA_INIT 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 encryption for the ISAKMP exchanges are provided by the authentication
mechanism and encryption algorithm selected. The key generation technique
selected creates keys for use by the authentication mechanism and encryp-
tion algorithm. The keys may also be used 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,
then new options can be picked during the negotiation phase (described in
Section 3.3) for use in protecting the actual data communications. If en-
cryption is not required for the SA, the encryption algorithm options are
not 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 ! # Sets/Lists ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SA Attribute Set/List #1 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SA Attribute Set/List #2 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SA Attribute Set/List #N ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: ISA_INIT_REQ and ISA_INIT_RESP Packet Format

o ISAKMP Header - Described in Section 2.1 2.3.2

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

_SA_Syntax__SA_Syntax_Type_
RESERVED 0
Set 1
List 2 Identifies the next payload in an ISAKMP
message if more then one is carried in a message.

o SA Flags Payload Length (1 octet) - Flags specific to Specifies the payload length in 4-octet
units.

o Situation - Variable length field containing the situation for an SA service. See
(described in section
2.3.5 for details. 2.3.1).

o Number of Sets (1 octet) Proposal - Number Variable length field containing a list of SA Attribute Sets being proposed
o
protection suites for an SA Attributes (variable) - A list (described in section 2.3.1).

The format and content of SA Attributes. both the situation and proposal is DOI-specific.
The SA Attribute
specifications are discussed format of the Internet Security situation and proposal is described in Section 2.3.1.
Appendix A.

3.1.1 SA Initialization Procedures

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

1. Create initiator cookie. See Section 2.3.4 2.3.7 for details.

2. Generate a unique pseudo-random negotiation SPI. See Section 2.1 2.3.2
for details.

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

4. Generate a proposal for protecting a session under that situation.

5. Construct an ISA_INIT_REQ packet.

6. Transmit the packet to the destination host as described in Section
2.1.1.
2.3.4.

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

1. Check the ISAKMP header as described in Section 2.1.1. 2.3.4.

2. Unpack the ISA_INIT_REQ payload payload.

3. Determine if the given situation can be protected. If not, the pro-
tocol machine must send a rejection notification and determine return to IDLE.

4. Determine if it can use any of the highest priority
attribute set (or attribute list) supported. proposed protection suites to
protect the session. If none of the proposed
attribute set (or list) is rejected, suites are acceptable,
then the protocol machine must send a rejection notification, clear
all state and return to IDLE.

5. Create responder cookie. See Section 2.3.4 2.3.7 for details.

6. Generate a unique pseudo-random SPI. See Section 2.1 2.3.2 for details.

7. 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 packet containing the SA Flags field MUST be set (see section 2.3.5 situation and 3.4).

6. the
chosen protection suite.

8. Transmit the packet to the initiating host as described in Section
2.1.1.
2.3.4.

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

1. Check the ISAKMP header as described in Section 2.1.1. 2.3.4.

2. Unpack the ISA_INIT_RESP payload.

3. Determine if the attribute set (or list) selected by that the responder situation returned is
valid. the same as the one sent.
If not, the protocol machine must send a rejection notification and
possibly resend the ISA_INIT_REQ message.

4. Determine if the returned protection suite is among the attribute set (or list) of valid
choices. If the entire proposal was rejected, the event
PROPOSAL_REJECTED is invalid or logged to the responder
rejected all proposed attribute sets (or lists), appropriate audit file. If an
invalid protection suite was returned, 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. Any further communication
must start the SA initialization procedures from the beginning.

If the attribute set (or list) is valid, a valid protection suite was selected, the receiving entity does
the following:

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

(b) Transition to Authentication and Key Exchange (see Section 3.2).

3.2 Authentication and Key Exchange

During the authentication and key exchange phase, information required to
confirm the identities of the parties wishing to establish the SA and es-
tablish a session key keys for use during the SA establishment is exchanged.
Depending on the key exchange algorithm, algorithms, the original key may be used dur-
ing
during data communications or a new one may be created and exchanged during dur-
ing the negotiation phase (described in section 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. 4. 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 5 and 7) 6) are general formats which support many types of authentication au-
thentication and key exchange mechanisms. The detailed specification of
these fields will be specified in companion RFCs. These companion RFCs
will define the standard authentication and key exchange mechanisms that
need to be implemented to assure compliance with this specification.

Figure 5: ISA_AUTH&KE_REQ The
format for the Internet Security DOI key exchange and ISA_AUTH&KE_RESP Packet Format authentication pay-
loads is described in A

3.2.1 Authentication 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 5.

o Authentication Authority (2 octets) - 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).

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

-- RSA Commercial Certificate Authority
(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) - 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 PKCS #7 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. The
type of certificate is indicated by the Authentication Type field.

3.2.2 Key Exchange 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 Oak-
ley [Oakley], Diffie-Hellman, the enhanced Diffie-Hellman key exchange described de-
scribed in X9.42 [ANSI94], [ANSI], the key exchange Key Exchange Algorithm (KEA) on the FORTEZZA
card, and the RSA-based key exchange used by PGP. This protocol will also
support key exchanges that include key escrow or data recovery techniques,
but does not mandate their use.

The encoding of the key exchange payload is dependent on the specific key
exchange 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

ISAKMP supports both public and private key generation techniques. Both
types must register with IANA to obtain a Key Exchange Identifier (KEI).

Before published public key exchanges can obtain a KEI, an RFC defining
the key exchange payload format and key generation procedures MUST be sub-
mitted. Private key exchanges SHOULD be documented in an RFC when regis-
tering for a KEI.

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 is sent
separately using the format described in 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.

3.2.3 Authentication and Key Exchange Procedures

When issuing an ISA_AUTH&KE_REQ 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.

6. Transmit the packet to the responding host as described in Section
2.1.1.
2.3.4.

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

1. Check the ISAKMP header as described in Section 2.1.1. 2.3.4.

2. Verify the initiator's signature. The ISA_AUTH&KE_REQ packet is
processed and the calculated signature is compared to the signature
contained in the ISA_AUTH&KE_REQ packet. 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.

(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. Unpack the ISA_AUTH&KE_REQ 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.

9. Transmit the packet to the initiating host as described in Section
2.1.1.
2.3.4.

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

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

1. Check the ISAKMP header as described in Section 2.1.1. 2.3.4.

2. Verify the initiator's signature. The ISA_AUTH&KE_RESP packet is
processed and the calculated signature is compared to the signature
contained in the ISA_AUTH&KE_RESP packet. 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.

(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. Calculate key, if necessary.

4. Transition to Security Association Negotiation.

3.3 Security Association Negotiation

The SA Negotiation phase allows the initiating entity to present SA at-
tributes that it wishes to use for secure communications to a respond-
ing entity. These SA attributes may include additional options for the
attributes agreed upon during the initialization phase, as well as ad-
ditional attributes required for an SA. As an example, the SA parame-
ters for the IP AH and IP ESP security mechanisms are cited in the Secu-
rity Architecture for the Internet Protocol [RFC-1825]. The format for
the ISA_NEG_REQ and ISA_NEG_RESP packets is the same as the ISA_INIT_REQ and
ISA_INIT_RESP shown in Figure 4. 3. All fields shown in Figure 4 3 exist for
the ISA_NEG_REQ and ISA_NEG_RESP packets.

3.3.1 SA Negotiation Procedures

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

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

2. 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. 2.

(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. 2.

4. Transmit the packet to the responding host as described in Section
2.1.1.
2.3.4.

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

1. Check the ISAKMP header as described in Section 2.1.1. 2.3.4.

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

(a) If the SA requires encryption, decrypt the ISA_NEG_REQ payload and
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 generate the appropriate information
and include it as an attribute in the ISA_NEG_RESP payload.

5. 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. 2.

(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. 2.

7. Transmit the packet to the initiating host as described in Section
2.1.1.
2.3.4.

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

9. Transition Return appropriate data (i.e. SA, SPI) to SA Negotation Conclusion (see Section 3.4). negotiation server, clear
all state, and return to IDLE.

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

1. Check the ISAKMP header as described in Section 2.1.1. 2.3.4.

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

(a) If the SA requires encryption, decrypt the ISA_NEG_RESP payload and
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 the attribute sets (or lists) are invalid
or the responder rejected all proposed 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 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 (see Section 3.4).

3.4 SA Negotiation Conclusion

The SA 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. If the entity ini-
tiating the SA establishment does not have the ability to queue incoming Return appropriate data it may receive prior to its completion of SA establishment process-
ing, then it requires the responding entity to wait for an SA_COMMIT mes-
sage before sending data. The transmittal of the ISA_COMMIT packet is op-
tional and determined by the policy of the parties establishing the SA.
All implementations MUST be able to generate, transmit, and receive this
message.

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. Construct an ISA_COMMIT packet (ISAKMP Header).

2. 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_COMMIT 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. Transmit the packet (i.e. SA, SPI) to the responding host as described in Section
2.1.1.

4. Clear negotiation server, clear
all state state, and return to IDLE.

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

1. Check the

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 as described in section 2.1.1.

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

(a) If the SA requires encryption, decrypt the ISA_COMMIT 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.

(b) If the SA requires authentication, the ISA_COMMIT packet is
processed Interpretation !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Situation ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Proposal ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: ISA_INIT_REQ and the calculated signature is compared to the
signature contained in the ISA_COMMIT packet. If these signatures
are not identical, the message is discarded ISA_INIT_RESP Packet Format

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 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload ! Payload Len ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
! Authentication Payload !
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload ! Payload Len ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
! Key Exchange Payload !
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: ISA_AUTH&KE_REQ and the following
actions are taken:

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

ii. Because the ISA_COMMIT packet is a unidirectional message a
retransmission will not be performed. Because the SA is
established, we recommend that communications can proceed,
however, the local security policy will dictate the
procedures for continuing. We recommend that an ISA_NOTIFY
packet with an Error Message ISA_AUTH&KE_RESP Packet Format
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload ! Payload Len ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Authentication Authority ! Reserved !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Authentication Type (see Section 6) be sent to
the originator ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
! Authentication Data !
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 5: Authentication Payload Format

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload ! Payload Len ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! KEI ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
! Key Exchange Data !
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 6: Key Exchange Payload Format

o KEI (2 octets) - Key Exchange Identifier

o Length (2 octets) - Length of the ISA_COMMIT packet.

3. Clear all state and return payload in octets

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

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 an existing SA.
The format for the ISA_MODIFY packet is 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. 3.

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.

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 (shown in Figure 8) 7) provides a controlled method of
informing a peer entity that the initiating entity has deleted an SA(s).
The ISA_DELETE packet allows for the deletion of any number of SAs with
a single message. The receiving entity SHOULD clean up its local SA
database. The receiving entity may be using the SA for secure communi-
cations with more than one party and would not want to actually delete the
SA from its database in this case. However, upon receipt of an ISA_DELETE
packet the SAs listed in the SPIs field of the packet cannot be used with
the initiating entity. The SA Establishment procedure must be invoked to
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 packet, the issuing entity (initiator or re-
sponder) does the following:

1. Create initiator cookie. See Section 2.3.4 2.3.7 for details.

2. Determine SPI of receiving entity.

3. Construct the ISA_DELETE packet.

4. 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. 2.

(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.
2.3.4.

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

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

Figure 7: SA Delete Payload Format

1. Check the ISAKMP header as described in Section 2.1.1. 2.3.4.

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.

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 wishes to communicate with a peer 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). B.2).
The ISA_NOTIFY packet is unidirectional.

Figure 9: 8: ISA NOTIFY Payload Format

o Notify Message Type (2 octets)

_Notification__Notify_Message_Type_

______Notification_______Notify_Message_Type__
RESERVED 0
Error 1 1-16383
Reserved for Future Use 16384-32767
Status 2 32768-49151
DOI Specific 49152-65536

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

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

6.1 Notify Message Types

Notify Messages - Errors Types
__________Errors___________Value_Payload__
DOI-NOT-SUPPORTED 1
SITUATION-NOT-SUPPORTED 2
INVALID-COOKIE 3
INVALID-VERSION-NO 4
INVALID-MESSAGE-TYPE 5
INVALID-EXCHANGE-TYPE 6
INVALID-SPI 7
ATTRIBUTES-NOT-SUPPORTED 8
NO-PROPOSAL-CHOOSEN 9
BAD-PROPOSAL-SYNTAX 10
ATTRIBUTES-NOT-SUPPORTED 11
INVALID-SIGNATURE 12
DECRYPTION-FAILED 13

Notify Messages - Status Types
__Status____Value____Payload____
CONNECTED 32769

6.2 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 2.3.7 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. 2.

(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.
2.3.4.

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. 2.3.4.

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 mas-
sive growth of the Internet will lead to great diversity in network utiliza-
tion, uti-
lization, communications, security requirements, and security requirements. mechanisms.
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 for future growth and diversity. This security diversity of multi-
ple key exchange techniques, encryption algorithms, authentication mecha-
nisms, security services, and security attributes will allow users to se-
lect the appropriate security for their network, communications, and secu-
rity needs. The SA feature allows users to specify and negotiate security
requirements with other users. An additional benefit of supporting multi-
ple techniques in a single protocol is that as new techniques are devel-
oped they can easily be added to the protocol. This 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 ISAKMP Scenarios

Examples scenerios IP Security DOI

The IP Security DOI Assigned Number for IPv4 is one (1). The situation
for DOI 1 is an IPv4 address. The IP Security DOI Assigned Number for
IPv6 is two (2). The situation for DOI 2 is an IPv6 address.

A.1 IP Security Proposal Formats

This section defines the IP Security syntax for SA proposals and secu-
rity attributes. The SA proposals for a security protocol (i.e. ESP) are
carried in an SA payload. The SA payload is sent in the following mes-
sages: ISA_INIT_REQ, ISA_INIT_RESP, ISA_NEG_REQ, ISA_NEG_RESP, ISA_MOD_REQ,
and
ISA_MOD_RESP. This syntax groups the security attributes needed to perform
a security function together. The proposal and attribute formats are presented de-
fined so additions or modifications to help illustrate the ISAKMP's abil-
ity proposals or attributes do not
require a modification to support multiple authentication methods and key exchanges.

A.1 Initial ISAKMP Daemon Scenerio

This example steps through two ISAKMP daemons establishing the protocol.

Figure 9 shows the SA proposal format which contains the SA attributes.
There can be one or more SA attribute in each SA proposal. There can one
or more SA proposals sent for each security protocol, but only one re-
sponse per security protocol is allowed. A negative response, such as:
IMPROPER SA PROPOSAL FORMAT, is returned in an ISA_NOTIFY message.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Protocol # ! Proposal # ! Proposal Len ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
+ +
. .
. SA between
themselves. This Attributes .
. .
+ +
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 9: SA uses DNS Proposal Format

o Protocol Number (1 octet) - Identifies the security protocol
requiring the SA attributes proposed. Uses the same values as the
IPv4 Protocol field [RFC-1700].

o Proposal Number (1 octet) - Unique proposal identifier for the given
security protocol.

o Proposal Length (1 octet) - Specifies the proposal length in 4-octet
units. Each IP Security Extentions [EK94] proposal is an integer multiple of 4 octets
long.

o SA Attributes - Variable length field containing the attributes for authentica-
tion and a Photuris [Karn95] compliant key exchange. Following
an SA.

Figure 10 shows the SA es-
tablishment between attribute format. The most significant bit of the daemons, SAs
Attribute Class defines a grouping of attributes within a proposal. The
second most significant bit indicates whether the attribute is of type
basic or variable percision integer (VPI). Negative responses, such as:
UNKNOWN SA ATTRIBUTE, are established returned in an ISA_NOTIFY message.

o Attribute Class (2 octets) - Unique identifier for ESP each general class
of attribute type. ENCRYPTION ALGORITHM is an example of an
attribute class. (See A.4 for the assigned attribute class values
for ESP, AH, and AH commu-
nications between user processes.

1. Oakley.)

The initiating daemon sends an ISA_INIT_REQ messages most significant bit (SET) of the Attribute Class is for indicating
a grouping of attributes within a proposal. If the SET bit is one (1)
the following attribute belongs with ISAKMP the current attribute. There can be
two or more attributes in a group. If the SET bit is zero (0) either the
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!S!T! ! TYP=0 VPI Length !
!E!Y! Attribute Class ! TYP=1 SA #3,
#2, and #1 (in priority order). These SAs are defined Attribute Value !
!T!P! ! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. TYP=0 VPI Present .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 10: Attribute Format

attribute is the last in C.1.1.

2. The responding daemon sends a set or is an ISA_INIT_RESP message indicating that
ISAKMP individual attribute. Attributes
should be grouped together when a security policy decision must be made
based on how attributes relate to each other, in addition to individual
meaning.

The second most significant bit (TYP) of the Attribute Class is for indi-
cating whether the attribute is a basic type or a variable percision inte-
ger (VPI). If the TYP bit is a zero (0) then the attribute is a VPI type.
If the TYP bit is a one (1) then the attribute is a basic type.

Figure 11 shows the basic SA #2 was selected, which requires DNS Signature and Key
Records attribute format and a Photuris compliant key exchange [DOW92].

3. Figure 12 shows the VPI
SA attribute format.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!S!1! Attribute Class ! SA Attribute Value !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 11: Basic Attribute Format

o Value (2 octets) - The initiating daemon sends an ISA_KE_REQ packet with value of the SA attribute as defined by the
Attribute class. (See A.5 for the assigned attribute values for IP
Security.)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!S!0! Attribute Class ! VPI Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. VPI .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 12: VPI Attribute Format

o VPI Length (2 octets) - Specifies the VPI's length in 4-octet units.
Each VPI is an index into
well-known table integer multiple of generator / prime pairs 4 octets long.

o VPI - Variable Percision Integer. The field is aligned so the most
significant bit is in the first 4-octet word following the VPI
Length.

A.2 ESP SA and it's public value.

4. Upon receipt of ISA_KE_REQ packet AH SA Proposals

The ESP and AH SAs are defined in [RFC-1825]. This section defines the responding daemon computes
format for the
shared secret ESP and session key.

5. AH SA proposals. The responding daemon sends an ISA_KE_RESP packet with attribute class fields are
as they would appear in an its public ESP or AH SA Proposal. The attribute value and both
VPI fields contain examples of the initiator information they would contain.

Note: The Lifetime fields (Key and responders public values signed
using its Private (Signature) SA) can be either basic or VPI at-
tributes. Therefore when parsing the Attribute Class, the TYP bit must
always be checked.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! AH ! Proposal # ! Proposal Len ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!1!1! Authentication Alg ! MD5 !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Authentication Mode ! KEYED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Auth Key and encrypted Exch Id ! Oakley New Group Mode !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!0! Key Lifetime ! 1!
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Time (in seconds) !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!0! SA Lifetime ! 1!
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Time (in seconds) !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!0! IP Source Address(es) ! 1!
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! IPv4 Address !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Sensitivity Level ! SECRET !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 13: AH Proposal Format
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! ESP ! Proposal # ! Proposal Len ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!1!1! Encryption Algorithm ! DES !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Encryption Mode ! CBC !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Encryption Transform ! RFC-1828 !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Enc Key Exch Id ! Oakley EXTERNAL KEY MODE !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!0! Crypotgraphic Synch ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! MPI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Replay Protection ! Present / Absent !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!1!1! Authentication Alg ! MD5 !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Authentication Mode ! KEYED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Auth Key Exch Id ! Oakley PRIVATE GROUP MODE !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Key Lifetime ! Time (in seconds) !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!0! SA Lifetime ! 1!
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Time (in seconds) !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!0! IP Source Address(es) ! 4!
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! IPv6 Address !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Sensitivity Level ! SECRET !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 14: ESP Proposal Format

A.3 Oakley Proposal

The Oakley proposal format contains the SA attributes that are exchanged
in the session ISA_INIT messages in order to establish the required security at-
tributes for the key
created.

6. Upon receipt and authentication exchange. See [Oakley] for fur-
ther details.

Note: The three figures 15, 16, and 17 are all combine to make one pro-
posal. They are shown seperately for reading and formatting ease.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Oakley ! Proposal # ! Proposal Len ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! EHA Format !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Group Format !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 15: Oakley Proposal Format

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Auth / Priv Flag ! PRIV !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Encryption Algorithm ! DES !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Hash Algorithm ! MD5 !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!1!1! Authentication Alg ! RSA !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!1! Authentication Mode ! KEYED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 16: Oakley Proposal - EHA Format
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!1!1! Group Description ! MODP !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!1!0! Field Size ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! MPI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!1!0! Prime ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! MPI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!1!0! Generator1 ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! MPI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!1!0! Generator2 ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! MPI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!1!0! Curve-p1 ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! MPI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!1!0! Curve-p2 ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! MPI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!1!0! Largest Prime Factor ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! MPI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!1!0! Order of ISA_KE_REQ packet Group ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! MPI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!0!0! Strength of Group ! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! MPI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 17: Oakley Proposal - Group Format

A.4 Attribute Class Assigned Numbers

Values for attribute classes are specified in the initiating daemon computes most recent ``Assigned
Numbers'' RFC [RFC-1700]. Presented in the
shared secret following tables are the val-
ues for ESP, AH, and session key.

7. The initiating daemon sends an ISA_AUTH_REQ packet with both Oakley SAs. In the
initiator Attribute Type Column, a ``B''
means basic encoding and responders public values signed using its ``V'' mean Variable Percision Integer.

AH and ESP Attribute Classes
___________________Class_____________________Assigned_Value__Attribute_Type__
RESERVED 0 x
RESERVED 1 x
Authentication Algorithm 2 B
Authentication Mode 3 B
Authentication KEI(s) 4 B
Encryption Algorithm 5 B
Encryption Mode 6 B
Encryption Transform 7 B
Encyption KEI(s) 8 B
Size of cryptographic synchronization or IV 9 B/V
Replay Protection 10 B
Key Lifetime 11 B/V
Rekey Value 12 B/V
SA Lifetime 13 B/V
IP Source Address(es) 14 V
Sensitivity Level 15 B

Oakley Attributes Classes
__________________Class____________________Assigned_Value__Attribute_Type__
Auth / Private
(Signature) Flag 16 B
Hash Algorithm 17 B
Group Description 18 B
Group Type 19 B
Field Element Size 20 V
Print (P) or Irreducible Field Polynomial 21 V
Generator (1 or 2 values) 22 V
Curve Parameters (2 values) 23 V
Largest Prime Factor of the Group Size 24 V
Order of the Group 25 V
Strength of Group 26 V

Attribute class values 27-1024 are reserved for IANA Use. Attribute
class values 1025-15360 are reserved for future use. Attribute class val-
ues 15360-16384 are reserved for private use.

A.5 Attribute Value Assigned Numbers

A.5.1 Sensitivity Level Assigned Numbers

Sensitivity Level
_____Level_____Assigned_Value
Not In Use 0
Unclassified 1
FOUO 2
Undefined 3
Confidential 4
Secret 5
Top Secret 6

Sensitivity values 7-1024 are reserved for IANA Use. Values 1025-15360
are reserved for future use. Values 15360-16384 are reserved for private
use.

A.5.2 Key and it's DNS name and Public (Verification) Exchange Identifiers (KEI) Assigned Numbers

Key
signed by it nameserver. All encrypted in Exchange Identifiers (KEI)
_____Key_Exchange_____Assigned_Value_
Reserved 0
Oakley Main Mode 1
Oakley ISAKMP Mode 2
Oakley Quick Mode 3
Oakley External Mode 4

KEI values 5-1024 are reserved for IANA Use. Values 1025-15360 are re-
served for future use. Values 15360-16384 are reserved for private use.

A.5.3 Encryption Transform Assigned Numbers

Encryption Transforms
_____Transform_____Assigned_Value
Reserved 0
RFC-1829 1
DES-CBC w/Replay 2

Encryption Transform values 3-1024 are reserved for IANA Use. Values
1025-15360 are reserved for future use. Values 15360-16384 are reserved
for private use.

B ISAKMP Scenarios

Examples scenerios are are presented to help illustrate the session ISAKMP's abil-
ity to support multiple authentication methods and key created.

8. The responding daemon sends an exchanges.

B.1 Oakley Scenario

___________|_______________Oakley_Scenario_____________________________Entity
N#1SI#1NTERNETNSE#2ntity #2
_______|| _______||

| | Establish Initial SA Between NSs| |
| | | |
| | ISA_INIT_REQ | |
| | ============> | |
| | ISA_INIT_RESP | |
| | <============ | |
| | | |
| | Oakley Key Exchange Between NSs | |
| | | |
| | ISA_KE_REQ | |
| | ==============> | |
| | ISA_KE_RESP | |
| | <=============== | |
| | | |
| | Oakley Authentication Exchange | |
| | | |
| | ISA_AUTH_REQ | |
| | ==============> | |
| | ISA_AUTH_RESP packet with it's DNS name | |
| | <=============== | |
| | ISA_AUTH_REQ | |
| | ==============> | |
| | ISA_AUTH_RESP | |
| | <=============== | |
| | | |
| | Protected Traffic | |
| | NS#1 to NS#2 | |
|_____|_ |______|

___________|_________Oakley_Scenario_continued______________________EntityN#
1SI#1NTERNETNSE#2ntity #2
_______|| _______||

| | SA Established NS#1 to NS#2 | |
| | | |
| |Establish SA Between Entities | |
| | | |
| | ISA_NEG_REQ | |
| | ============> | |
| | ISA_NEG_RESP | |
| | <============ | |
| | | |
| | Oakley External Key Exchange | |
| | Between Entities | |
| | | |
| | ISA_KE_REQ | |
| | ==============> | |
| | ISA_KE_RESP | |
| | <=============== | |
| | ISA_KE_REQ | |
| | ==============> | |
| | | |
| | | |
| | Protected Traffic | |
| | Entity#1 to Entity#2 | |
|______| <==============> |______|

The diagrams above only shows ISAKMP messages exchanges. Shown are the
exchanges to initiate SAs between entities and Public (Verification) signed by it Secure DNS nameserver negotiation servers and
encrypted in
the session exchanges for the Oakley key created.

9. exchange and authentication. The initiating daemon sends formats
and contents of the messages can be found in [Oakley] and Appendix A. See
Section 2.1 for the relationship of ISAKMP to the protocol stack.

When an ISA_NEG_REQ packet entity, which can be a process, application, security protocol,
etc., wishes to establish communications with ESP a peer entity a call is made
to the negotiation server (NS). NS#1 checks the local security policy to
determine if an SA #2, ESP is required. If an SA #1, AH is required, then NS#1 checks
if it has the appropriate SAs established with the peer NS (NS#2). If a
negotiation SA #1, and AH (NS-to-NS SA) is exists, NS#1 can proceed to the start of
the second diagram. If a negotiation SA #2. These SAs needs to be established, the NSs
exchange ISA_INIT messages to determine the security attributes, key ex-
change, and authentication to be used for the negotiation SA. In our exam-
ple the Oakley key exchange and authentication is choosen. The ISA_KE and
ISA_AUTH messages are exchanged according to the rules defined in C.2.1.

10. the key
exchange. Oakley requires two key exchange messages and four authentica-
tion messages. Once these exchanges are complete a negotiation SA between
NSs is established. In the second diagram the negotiation SA is used to
protect the remaining exchanges shown. The responding daemon sends an ISA_NEG_RESP packet indicating that ESP NSs now exchange ISA_NEG mes-
sages to create a SA #2, and AH for the entity itself. In our example an Oakley Ex-
ternal Key Exchange is now performed to establish a new key for the entity
to entity SA. Once this SA #1 was selected.

A.2 is established, protected communications takes
place.

B.2 Virtual Private Network Scenario

This scenario show shows how ISAKMP can be used in a Virtual Public Network
(VPN). The ability to establish SAs for more than just ESP and AH and one
of the uses of the ISA_NOTIFY message are also illustrated.

___________________________Virtual_Public_Network_Scenario_______________________
End System#1 SFE#1 INTERNET SFE#2 End

__________________|_________Virtual_Public_Network_Scenario____________________
____________EndSSystemF#1EI#1NTERNETSFEE#2nd 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 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 SA_NOTIFY ISA_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 ISA_NOTIFY
with Status equal Not Connected with an optional reason code.

C 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.

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

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

11. FRAGMENTATION

(a) INBOUND

(b) OUTBOUND

12. KEY-MANAGEMENT

(a) NEGOTIATED

(b) TECHNIQUE

(d) REKEY

o GRACE

o NEXT-SA

o TIME-BASED

i. ENABLE

ii. TRIGGER

o TRAFFIC-BASED

i. ENABLE

ii. PACKET-COUNT.INBOUND

iii. PACKET-COUNT.OUTBOUND
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
[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 pro-
vided significant input and review to this document.

Scott Carlson ported the TIS DNSSEC prototype to FreeBSD for use with the
ISAKMP prototype.

Jeff Turner and Steve Smalley have contributed to the prototype develop-
ment and integration with ESP and AH.

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

References

[ANSI94]

[ANSI] ANSI, X9.42: Public Key Cryptography for the Financial Services
Industry -- Establishment of Symmetric Algorithm Keys Using
Diffie-Hellman, Working Draft, October 26, 1995.

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

[BC] Ballarie, A. and J. Crowcroft, Multicast-specific Security Threats
and Countermeasures, Proceedings of 1995 ISOC Symposium on Networks
& Distributed Systems Security, pp. 17-30, Internet Society, San
Diego, CA, February 1995.

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

[DOW92] W. Diffie, M.Wiener, P. Van Oorschot, Authtication Authentication 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, work
in progress, November, 1995.

[EK94]

[DNSSEC] Eastlake III, D. and C. Kaufman, Domain Name System Protocol
Security Extensions, Internet-Draft, work in progress, Oct, 1995.

[Karn95] Feb, 1996.

[Karn] Karn P. and B. Simpson, The Photuris Key Management Protocol,
Internet-Draft, work in progress, November, 1995. February, 1996.

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

[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

[Oakley] H. K. Orman, The Oakley Key Management, RFC-1422, February 1993.

[RFC-1825] Randell Atkinson, Security Architecture for the Internet Determination Protocol, RFC-1825, August, 1995.
Internet-Draft, work in progress, February, 1996.

[RFC-1700] Reynolds, J. and J. Postel, Assigned Numbers, STD 2, RFC-1700,
October, 1994.

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

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

[Schn94]

[Schneier] 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 two authors are with:

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

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

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