Cryptographic Algorithm Implementation Requirements for Encapsulating Security Payload (ESP) and Authentication Header (AH)
RFC 4305

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Network Working Group                                    D. Eastlake 3rd
Request for Comments: 4305                         Motorola Laboratories
Obsoletes: 2404, 2406                                      December 2005
Category: Standards Track

        Cryptographic Algorithm Implementation Requirements for
  Encapsulating Security Payload (ESP) and Authentication Header (AH)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   The IPsec series of protocols makes use of various cryptographic
   algorithms in order to provide security services.  The Encapsulating
   Security Payload (ESP) and the Authentication Header (AH) provide two
   mechanisms for protecting data being sent over an IPsec Security
   Association (SA).  To ensure interoperability between disparate
   implementations, it is necessary to specify a set of mandatory-to-
   implement algorithms to ensure that there is at least one algorithm
   that all implementations will have available.  This document defines
   the current set of mandatory-to-implement algorithms for ESP and AH
   as well as specifying algorithms that should be implemented because
   they may be promoted to mandatory at some future time.

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RFC 4305         Cryptographic Algorithms for ESP & AH     December 2005

Table of Contents

   1. Introduction ....................................................2
   2. Requirements Terminology ........................................3
   3. Algorithm Selection .............................................3
      3.1. Encapsulating Security Payload .............................3
           3.1.1. ESP Encryption and Authentication Algorithms ........4
           3.1.2. ESP Combined Mode Algorithms ........................4
      3.2. Authentication Header ......................................5
   4. Security Considerations .........................................5
   5. Acknowledgement .................................................5
   6. Changes from RFC 2402 and 2406 ..................................6
   7. Normative References ............................................6
   8. Informative References ..........................................7

1.  Introduction

   The Encapsulating Security Payload (ESP) and the Authentication
   Header (AH) provide two mechanisms for protecting data being sent
   over an IPsec Security Association (SA) [IPsec, ESP, AH].  To ensure
   interoperability between disparate implementations, it is necessary
   to specify a set of mandatory-to-implement algorithms to ensure that
   there is at least one algorithm that all implementations will have
   available.  This document defines the current set of mandatory-to-
   implement algorithms for ESP and AH as well as specifying algorithms
   that should be implemented because they may be promoted to mandatory
   at some future time.

   The nature of cryptography is that new algorithms surface
   continuously and existing algorithms are continuously attacked.  An
   algorithm believed to be strong today may be demonstrated to be weak
   tomorrow.  Given this, the choice of mandatory-to-implement algorithm
   should be conservative so as to minimize the likelihood of it being
   compromised quickly.  Thought should also be given to performance
   considerations as many uses of IPsec will be in environments where
   performance is a concern.

   Finally, we need to recognize that the mandatory-to-implement
   algorithm(s) may need to change over time to adapt to the changing
   world.  For this reason, the selection of mandatory-to-implement
   algorithms is not included the main IPsec, ESP, or AH specifications.
   It is instead placed in this document.  As the choice of algorithm
   changes, only this document should need to be updated.

   Ideally, the mandatory-to-implement algorithm of tomorrow should
   already be available in most implementations of IPsec by the time it
   is made mandatory.  To facilitate this, we will attempt to identify
   such algorithms (as they are known today) in this document.  There is

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RFC 4305         Cryptographic Algorithms for ESP & AH     December 2005

   no guarantee that the algorithms we believe today may be mandatory in
   the future will in fact become so.  All algorithms known today are
   subject to cryptographic attack and may be broken in the future.

2.  Requirements Terminology

   Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and