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-01.txt>
Status of This Memo
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This memo provides information for the Internet community. This memo
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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.
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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 Algorithm Documents .......................6
4.1 Encryption and Authentication Algorithms ........................6
4.2 Encryption Algorithms ...........................................7
4.3 Authentication Algorithms .......................................8
5. Security Considerations ..........................................8
6. Acknowledgments ..................................................9
7. References .......................................................9
8. Author's Addresses ..............................................10
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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 RFC status. 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-1829], [DES-Detroit], [3DES], or [CAST] 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.
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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.
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+--------------+
| 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 lengths. The key management pro-
tocols 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 ESP
protocol document is responsible for specifying how the keys are
extracted from the keying material (sliced and diced). The Encryption
Algorithm and Authentication Algorithm documents are responsible for
specifying the key sizes and strengths for each algorithm. However,
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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 docu-
ment 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 go in the DOI document.
Encryption and authentication algorithms require some set of optional
parameters or have optional modes of operation (e.g. IVs, authentica-
tion data lengths, and key lengths). To help eliminate some complex-
ity 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
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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.
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.
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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 docu-
ment.
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 Encryp-
tion 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 algo-
rithms are not considered secure if they are not used with some sort
of authentication mechanism.
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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.
. 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
[3DES] Doraswamy, N., Metzger, P., Simpson, W.A., "The ESP
Triple DES Transform",
draft-ietf-ipsec-ciph-des3-00.txt, July 1997.
[Arch] Atkinson, R., "Security Architecture for the Internet
Protocol", RFC-1825, Naval Research Laboratory,
July 1995.
[CAST] Pereira, R., Carter, G., "The ESP CAST128-CBC
Algorithm", draft-ietf-ipsec-ciph-cast128-cbc-00.txt,
July 1997.
[DES-Detroit] Madson, C., "The ESP DES-CBC Cipher Algorithm With
Explicit IV", draft-ietf-ipsec-ciph-des-expiv-00.txt,
July 1997.
[DES-1829] Metzger, P., Simpson, W.A., "The ESP DES-CBC
Transform", draft-ietf-ipsec-ciph-des-derived-00.txt,
July 1997.
[DOI] IP Security Domain of Interpretation, RFC-xxxx.
[AH] Kent, S., Atkinson, R., "IP Authentication Header",
draft-ietf-ipsec-auth-header-01.txt, July 1997.
[ESP] Kent, S., Atkinson, R., "IP Encapsulating Security
Payload (ESP)", draft-ietf-ipsec-esp-v2-00.txt,
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July 1997.
[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-hmac-md5-96-00.txt,
July 1997.
[HMAC-SHA-1] Madson, C., Glenn, R., "The Use of HMAC-SHA-1 within
ESP and AH", draft-ietf-ipsec-auth-hmac-sha196-00.txt,
July 1997.
[RANDOM] Eastlake, D., Crocker, S., Schiller, J., "Randomness
Recommendations for Security", RFC-1750,
December 1994.
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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