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Network Working Group R. Thayer
Internet Draft N. Doraswamy
Category: Informational R. Glenn
Expire in six months July 1997
IP Security
Document Roadmap
<draft-ietf-ipsec-doc-roadmap-00.txt>
Status of This Memo
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
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as ``work in progress.''
To learn the current status of any Internet-Draft, please check the
``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast).
This memo provides information for the Internet community. This memo
does not specify an Internet standard. Distribution of this memo is
unlimited.
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 Cipher and Authenticator documents are
described.
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Contents
Status of This Memo .................................................1
Abstract ............................................................1
Contents ............................................................2
1. Introduction .....................................................3
2. Interrelationship of IPsec Documents .............................3
3. Keying Material ..................................................5
4. Recommended Content of Cipher and Authenticator Documents ........5
4.1 Cipher and Authenticator ........................................5
4.2 Cipher ..........................................................6
4.3 Authenticator ...................................................7
5. Security Considerations ..........................................8
6. Acknowledgments ..................................................8
7. References .......................................................9
8. Author's Addresses ...............................................9
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1. Introduction
This document is intended to provide guidelines for the development
of collateral specifications describing the use of new Cipher and
Authenticator algorithms with the ESP protocol, described in [ESP]
and new Authenticator 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 cipher algorithms or
authenticator algorithms to ESP and AH, not only while the initial
document set is undergoing development but after the base documents
have achieved RFC status. Following the guidelines discussed below
simplifies adding new algorithms and reduces that amount of redundant
documentation.
The goal in writing a new ESP or AH algorithm document is to
concentrate on the application of the specific algorithm. 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 "Cipher" document set, shown on the left, is the set of documents
describing how various ciphers 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 Authenticator documents. Examples
of this document are the [DES-1829], [DES-Detroit], [3DES], or [CAST]
documents. When these or other Ciphers are used for ESP, the DOI
document has to indicate certain values, such as Cipher type, so
these documents provide input to the DOI.
The "Authenticator" document set, shown on the right, is the set of
documents describing how various authenticator algorithms are used
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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 Cipher 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
Cipher algorithms, Authenticator 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 | | | | | | v
v +-| Cipher | +-| Authenticator | v
v +--------+ +---------------+ v
v v v v
v v +-----+ v v
+>->->->-+->->->->| DOI |<-<-<-<-+-<-<-<-<-+
+-----+
^
^
+------------+
| KEY |
| MANAGEMENT |
+------------+
Figure 1. IPsec Document Roadmap.
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3. Keying Material
Describing the cipher and authenticator algorithms in different docu-
ments 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" informa-
tion.
Each cipher and authenticator document should specify their respec-
tive key lengths. The key management protocols should use the length
of the keys specified in the cipher and authenticator documents to
generate the keying material of required length.
The ESP protocol document is responsible for specifying how the keys
are extracted from the keying material (sliced and diced). For exam-
ple, it should specify if the cipher or the authenticator algorithm
uses the first n-bits in the provided keying material. The AH proto-
col document has no such requirement. [Editor's Note: This paragraph
is still under contention and will be modified once the location of
the key derivation mechanism is known].
4. Recommended Content of Cipher and Authenticator Documents
The document describing how a specific cipher or authenticator is
used should contain information appropriate to that cipher or authen-
ticator. This section enumerates what information should be pro-
vided. 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 go in the DOI document.
Cipher and Authenticator algorithms require some set of optional
parameters or have optional modes of operation (e.g. IVs, authentica-
tor lengths, and key lengths). To help eliminate some complexity
involved with key management having to negotiate large numbers of
algorithm-specific parameters, Cipher and Authenticator 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 Cipher and Authenticator
This section describes the information that should be included in
both Cipher and Authenticator 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.
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. 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 authentication and cipher 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.
4.2 Cipher
This section describes the information that should be included in
Cipher documents.
Cipher Description
. General information how this cipher algorithm is to be used in
ESP.
. Description of background material and formal algorithm
description.
. Features of this cipher 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
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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 Authenticator
This section describes the information that should be included in
Authenticator documents. In most cases, an authenticator algorithm
will operate the same whether it is used for ESP or AH. This should
be represented in a single authenticator algorithm document.
Authenticator Description
. General information on how this authenticator algorithm is to be
used with ESP and AH.
. Description of background material and formal algorithm
description.
. Features of this authenticator.
. 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 authenticator 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.
. Authenticator comparison criteria for this algorithm. Note: There
is a default method for verifying the authenticator specified
in the AH protocol document. This is only needed if the default
cannot be used (e.g. when using a signed hash).
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5. Security Considerations
This document provides a roadmap and guidelines for writing cipher
and authenticator documents. The reader SHOULD follow all the secu-
rity procedures and guidelines described in the IPsec Architecture,
ESP, AH, cipher and authenticator documents. Note that many cipher
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 RFC repositories.
In certain cases the reader may want to know what version of these
documents were referenced. These documents are:
. ARCH: draft-ietf-ipsec-arch-sec-01.txt.
. 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.
. DES-1829: this is Bill Simpson's DES-CBC for ESP document, to be
published as draft-simpson-esp-des1-v2-01.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.
. DOI: draft-ietf-ietf-doi-02.txt.
. 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.
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7. References
[3DES] Triple-DES for ESP, RFC-xxxx.
[ARCH] Atkinson, R., "Security Architecture for the Internet
Protocol", RFC-1825, Naval Research Laboratory,
July 1995.
[CAST] CAST for ESP, RFC-xxxx.
[DES-Detroit] DES for ESP, Detroit dialect, RFC-xxxx.
[DES-1829] DES for ESP, 1829-Compatible mode, RFC-xxxx.
[DOI] IP Security Domain of Interpretation, RFC-xxxx.
[ESP] Karn, P., Metzger, P., and W. Simpson, "The ESP DES-CBC
Transform", RFC 1829, Qualcomm, Inc., Piermont,
Daydreamer, August 1995.
[HMAC] Krawczyk, K., Bellare, M., and Canetti R., "HMAC:
Keyed-Hashing for Message Authentication", RFC-2104,
February 1997.
[HMAC-MD5] Madson, C., Glenn, R., "The Use of HMAC-MD5 within ESP
and AH", draft-ietf-ipsec-ff-auth-hmac-sha-1-00.txt,
June 1997.
[HMAC-SHA-1] Madson, C., Glenn, R., "The Use of HMAC-SHA-1 within
ESP and AH", draft-ietf-ipsec-ff-auth-hmac-sha-1-00.txt,
June 1997.
8. Author's Addresses
Rodney Thayer
Sable Technology Corporation
246 Walnut Street
Newton, Massachusetts 02160
<mailto:rodney@sabletech.com>
Naganand Doraswamy
Bay Networks
e-mail: naganand@baynetworks.com
Rob Glenn
NIST
e-mail: rob.glenn@nist.gov
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