Network Working Group R. Thayer
Request for Comments: 2411 Sable Technology Corporation
Category: Informational N. Doraswamy
Bay Networks
R. Glenn
NIST
November 1998

IP Security
Document Roadmap

Status of this Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (1998). All Rights Reserved.

Abstract

The IPsec protocol suite is used to provide privacy and
authentication services at the IP layer. Several documents are used
to describe this protocol suite. The interrelationship and
organization of the various documents covering the IPsec protocol are
discussed here. An eXPlanation of what to find in which document,
and what to include in new Encryption Algorithm and Authentication
Algorithm documents are described.

Table of Contents

1. IntrodUCtion ................................................2
2. Interrelationship of IPsec Documents ........................2
3. Keying Material .............................................4
4. Recommended Content of Algorithm Documents ..................5
4.1 Encryption and Authentication Algorithms ...................5
4.2 Encryption Algorithms ......................................6
4.3 Authentication Algorithms ..................................7
5. Security Considerations .....................................8
6. Acknowledgments .............................................8
7. References ..................................................9
8. Authors' Addresses .........................................10
9. Full Copyright Statement ...................................11

1. Introduction

This document is intended to provide guidelines for the development
of collateral specifications describing the use of new encryption and
authentication algorithms with the ESP protocol, described in [ESP]
and new authentication algorithms used with the AH protocol,
described in [AH]. ESP and AH are part of the IP Security
architecture described in [Arch]. There is a requirement for a
well-known procedure that can be used to add new encryption
algorithms or authentication algorithms to ESP and AH, not only while
the initial document set is undergoing development but after the base
documents have achieved RFCstatus. Following the guidelines
discussed below simplifies adding new algorithms and reduces that
amount of redundant documentation.

The goal in writing a new Encryption Algorithm or Authentication
Algorithm document is to concentrate on the application of the
specific algorithm within ESP and AH. General ESP and AH concepts,
definitions, and issues are covered in the ESP and AH documents. The
algorithms themselves are not described in these documents. This
gives us the capability to add new algorithms and also specify how
any given algorithm might interact with other algorithms. The intent
is to achieve the goal of avoiding duplication of information and
excessive numbers of documents, the so-called "draft explosion"
effect.

2. Interrelationship of IPsec Documents

The documents describing the set of IPsec protocols are divided into
seven groups. This is illustrated in Figure 1. There is a main
Architecture document which broadly covers the general concepts,
security requirements, definitions, and mechanisms defining IPsec
technology.

There is an ESP Protocol document and an AH Protocol document which
covers the packet format and general issues regarding the respective
protocols. These protocol documents also contain default values if
appropriate, such as the default padding contents, and mandatory to
implement algorithms. These documents dictate some of the values in
the Domain Of Interpretation document [DOI]. Note the DOI document
is itself part of the IANA Assigned Numbers mechanism and so the
values described in the DOI are well-known. See [DOI] for more
information on the mechanism.

The "Encryption Algorithm" document set, shown on the left, is the
set of documents describing how various encryption algorithms are
used for ESP. These documents are intended to fit in this roadmap,
and should avoid overlap with the ESP protocol document and with the

Authentication Algorithm documents. Examples of this document are
the [DES-Detroit] and [CBC] documents. When these or other
encryption algorithms are used for ESP, the DOI document has to
indicate certain values, such as an encryption algorithm identifier,
so these documents provide input to the DOI.

The "Authentication Algorithm" document set, shown on the right, is
the set of documents describing how various authentication algorithms
are used for both ESP and AH. These documents are intended to fit in
this roadmap, and should avoid overlap with the AH protocol document
and with the Encryption Algorithm documents. Examples of this
document are the [HMAC-MD5], and [HMAC-SHA-1] documents. When these
or other algorithms are used for either ESP or AH, the DOI document
has to indicate certain values, such as algorithm type, so these
documents provide input to the DOI.

The "Key Management Documents", shown at the bottom, are the
documents describing the IETF standards-track key management schemes.
These documents provide certain values for the DOI also. Note that
issues of key management should be indicated here and not in, for
example, the ESP and AH protocol documents. Currently this box
represents [ISAKMP], [Oakley], and [Resolution].

The DOI document, shown in the middle, contains values needed for the
other documents to relate to each other. This includes for example
encryption algorithms, authentication algorithms, and operational
parameters such as key lifetimes.

+--------------+
Architecture
+--------------+
v v
+<-<-<-<-+ +->->->->+
v v
+----------+ +----------+
ESP AH
Protocol Protocol
+----------+ +----------+
v v v v
v +->->->->->->->->+ v v
v v v v v
v v v v v
v +------------+ +----------------+ v
v +------------+ +----------------+ v
v Encryption Authentication v
v +- Algorithm +- Algorithm v
v +------------+ +----------------+ v
v v v v
v v +-----+ v v
+>->->->-+->->->-> DOI <-<-<-<-+-<-<-<-<-+
+-----+
^
^
+------------+
KEY
MANAGEMENT
+------------+

Figure 1. IPsec Document Roadmap.

3. Keying Material

Describing the encryption and authentication algorithms in different
documents raises the issue of how the key management protocols knows
the required keying material length for the desired algorithms when
used together with ESP. It also raises the issue of how to divide
the keying material. This is known as the "slicing and dicing"
information.

Each Encryption Algorithm and Authentication Algorithm document
should specify their respective key attributes (e.g. how to pad,
location of parity bits, key order for multi-keyed algorithms, and
length). The key management protocols should use the length of the
keys specified in the respective Algorithm documents to generate the
keying material of required length.

The key management protocol generates keying material with enough
strength and size to generate keys for individual algorithms. The
IPsec Architecture document specifies how keys are extracted from a
single block of keying material when multiple keys are required (e.g.
ESP with authentication). The Encryption Algorithm and

Authentication Algorithm documents are responsible for specifying the
key sizes and strengths for each algorithm. However, whether the
entire keying material is passed down to the kernel to perform
slicing and dicing or if the keys are sliced and diced by key
management protocol is an implementation issue. The AH protocol
document has no such requirement.

4. Recommended Content of Algorithm Documents

The document describing how a specific encryption or authentication
algorithm is used should contain information appropriate to that
encryption or authentication algorithm. This section enumerates what
information should be provided. It is the intention of the document
roadmap that:

. General protocol information goes in the respective ESP or AH
protocol documents.
. Key management information goes in the key management documents.
. Assigned values and constants of negotiable items go in the DOI
document.

Encryption and authentication algorithms require some set of optional
parameters or have optional modes of operation (e.g. IVs,
authentication data lengths, and key lengths). To help eliminate
some complexity involved with key management having to negotiate
large numbers of algorithm-specific parameters, encryption and
authentication algorithm documents will select fixed values for these
parameters when it is deemed technically reasonable and feasible.

Note, the following information is intended as a general guideline
only.

4.1 Encryption and Authentication Algorithms

This section describes the information that should be included in
both Encryption Algorithm and Authentication Algorithm documents.

Keying Material

. Size of keys, including minimum, maximum, recommended and/or
required sizes. Note: the security considerations section should
address any weakness in specific sizes.

. Recommended or required pseudo-random number generator techniques
and attributes to provide sufficiently strong keys. [RANDOM]
provides recommendations on generating strong randomness for use
with security.
. Format of keying material.
. Known weak keys or references to documentation on known weak keys.
. Recommended or required processing of input keying material such
as parity generation or checking.
. Requirements and/or recommendations on how often the keying
material should be refreshed.

Performance Considerations
. Any available estimates on performance of this algorithm.
. Any available comparison data (e.g., compared against DES or
MD5).
. Input size or other considerations that could improve or degrade
performance.

ESP Environmental Considerations
. Any known issues regarding interactions between this algorithm and
other ASPects of ESP, such as use of certain authentication
schemes. Note: As new encryption and authentication algorithms
are applied to ESP, the later documents will be required to
address interactions with previously specified algorithms.

Payload Content and Format Description
. Specification of size, placement, and content of algorithm-
specific fields not defined in the ESP or AH protocol documents
(e.g., IV).

Security Considerations
. Discuss any known attacks.
. Discuss any known common implementation pitfalls, such as use of
weak random number generators.
. Discuss any relevant validation procedures, such as test vectors.
[RFC-2202] is an example document containing test vectors for
a set of authentication algorithms.

4.2 Encryption Algorithms

This section describes the information that should be included in the
Encryption Algorithm documents.

Encryption Algorithm Description
. General information how this encryption algorithm is to be used in
ESP.
. Description of background material and formal algorithm
description.

. Features of this encryption algorithm to be used by ESP, including
encryption and/or authentication.
. Mention of any availability issues such as Intellectual Property
considerations.
. References, in IETF style, to background material such as FIPS
documents.

Algorithm Modes of Operation
. Description of how the algorithm is operated, whether it is block
mode or streaming mode or other.
. Requirements for input or output block format.
. Padding requirements of this algorithm. Note: there is a default
for padding, specified in the base ESP document, so this is only
needed if the default cannot be used.
. Any algorithm-specific operating parameters, such as number of
rounds.
. Identify optional parameters and optional methods of operation and
pick reasonable fixed values and methods with explicit technical
explanations.
. Identify those optional parameters in which values and methods
should remain optional with explicit technical explanations on why
fixed values and methods should not be used.
. Defaults and mandatory ranges on algorithm-specific optional
parameters that could not be fixed.

4.3 Authentication Algorithms

This section describes the information that should be included in the
Authentication Algorithm documents. In most cases, an authentication
algorithm will operate the same whether it is used for ESP or AH.
This should be represented in a single Authentication Algorithm
document.

Authentication Algorithm Description
. General information on how this authentication algorithm is to be
used with ESP and AH.
. Description of background material and formal algorithm
description.
. Features of this authentication algorithm.
. Mention of any availability issues such as Intellectual Property
considerations.
. References, in IETF style, to background material such as
FIPS documents and definitive descriptions of underlying
algorithms.

Algorithm Modes of Operation
. Description of how the algorithm is operated.

. Algorithm-specific operating parameters, such as number of
rounds, and input or output block format.
. Implicit and explicit padding requirements of this algorithm.
Note: There is a default method for padding of the
authentication data field specified in the AH protocol document.
This is only needed if the default cannot be used.
. Identify optional parameters and optional methods of operation and
pick reasonable fixed values and methods with explicit technical
explanations.
. Identify those optional parameters in which values and methods
should remain optional with explicit technical explanations on why
fixed values and methods should not be used.
. Defaults and mandatory ranges on algorithm-specific optional
parameters that could not be fixed.
. Authentication data comparison criteria for this algorithm. Note:
There is a default method for verifying the authentication data
specified in the AH protocol document. This is only needed if the
default cannot be used (e.g. when using a signed hash).

5. Security Considerations

This document provides a roadmap and guidelines for writing
Encryption and Authentication Algorithm documents. The reader should
follow all the security procedures and guidelines described in the
IPsec Architecture, ESP Protocol, AH Protocol, Encryption Algorithm,
and Authentication Algorithm documents. Note that many encryption
algorithms are not considered secure if they are not used with some
sort of authentication mechanism.

6. Acknowledgments

Several Internet drafts were referenced in writing this document.
Depending on where the documents are on (or off) the IETF standards
track these may not be available through the IETF RFCrepositories.
In certain cases the reader may want to know what version of these
documents were referenced. These documents are:

. DES-Detroit: this is the ANX Workshop style of ESP, based on the
Hughes draft as modified by Cheryl Madson and published on the ANX
mailing list.
. DOI: draft-ietf-ipsec-ipsec-doi-02.txt.
. 3DES: this is <the Triple-DES shim document>.
. CAST: this is draft-ietf-ipsec-esp-cast-128-cbc-00.txt, as revised
to relate to this document.
. ESP: draft-ietf-ipsec-esp-04.txt, mailed to the IETF mailing list
in May/June 1997.
. AH: draft-ietf-ipsec-auth-05.txt, mailed to the IETF mailing list
in May/June 1997.

. HUGHES: this is draft-ietf-ipsec-esp-des-md5-03.txt
. ISAKMP: There are three documents describing ISAKMP. These are
draft-ietf-ipsec-isakmp-07.txt, draft-ietf-ipsec-isakmp-oakley-
03.txt, and draft-ietf-ipsec-ipsec-doi-02.txt.

7. References

[CBC] Periera, R., and R. Adams, "The ESP CBC-Mode Cipher
Algorithms", RFC2451, November 1998.

[Arch] Kent, S., and R. Atkinson, "Security Architecture for
the Internet Protocol", RFC2401, November 1998.

[DES-Detroit] Madson, C., and N. Doraswamy, "The ESP DES-CBC Cipher
Algorithm With Explicit IV", RFC2405, November 1998.

[DOI] Piper, D., "The Internet IP Security Domain of
Interpretation for ISAKMP", RFC2407, November 1998.

[AH] Kent, S., and R. Atkinson, "IP Authentication Header",
RFC2402, November 1998.

[ESP] Kent, S., and R. Atkinson, "IP Encapsulating Security
Payload (ESP)", RFC2406, November 1998.

[HMAC] Krawczyk, K., Bellare, M., and R. Canetti, "HMAC:
Keyed-Hashing for Message Authentication", RFC2104,
February 1997.

[HMAC-MD5] Madson, C., and R. Glenn, "The Use of HMAC-MD5 within
ESP and AH", RFC2403, November 1998.

[HMAC-SHA-1] Madson, C., and R. Glenn, "The Use of HMAC-SHA-1 within
ESP and AH", RFC2404, November 1998.

[RANDOM] Eastlake, D., Crocker, S., and J. Schiller, "Randomness
Recommendations for Security", RFC1750, December 1994.

[RFC-2202] Cheng, P., and R. Glenn, "Test Cases for HMAC-MD5 and
HMAC-SHA-1", RFC2202, March 1997.

8. Authors' Addresses

Rodney Thayer
Sable Technology Corporation
246 Walnut Street
Newton, Massachusetts 02160

EMail: mailto:rodney@sabletech.com

Naganand Doraswamy
Bay Networks

EMail: naganand@baynetworks.com

Rob Glenn
NIST

EMail: rob.glenn@nist.gov

9. Full Copyright Statement

Copyright (C) The Internet Society (1998). All Rights Reserved.

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