The ESP CBC-Mode Cipher Algorithms
RFC 2451

Document Type RFC - Proposed Standard (November 1998; No errata)
Last updated 2013-03-02
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Network Working Group                                       R. Pereira
Request for Comments: 2451                        TimeStep Corporation
Category: Standards Track                                     R. Adams
                                                    Cisco Systems Inc.
                                                         November 1998

                   The ESP CBC-Mode Cipher Algorithms

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 (1998).  All Rights Reserved.

Abstract

   This document describes how to use CBC-mode cipher algorithms with
   the IPSec ESP (Encapsulating Security Payload) Protocol.  It not only
   clearly states how to use certain cipher algorithms, but also how to
   use all CBC-mode cipher algorithms.

Table of Contents

   1. Introduction...................................................2
     1.1 Specification of Requirements...............................2
     1.2 Intellectual Property Rights Statement......................2
   2. Cipher Algorithms..............................................2
     2.1 Mode........................................................3
     2.2 Key Size....................................................3
     2.3 Weak Keys...................................................4
     2.4 Block Size and Padding......................................5
     2.5 Rounds......................................................6
     2.6 Backgrounds.................................................6
     2.7 Performance.................................................8
   3. ESP Payload....................................................8
     3.1 ESP Environmental Considerations............................9
     3.2 Keying Material.............................................9
   4. Security Considerations........................................9
   5. References....................................................10
   6. Acknowledgments...............................................11
   7. Editors' Addresses............................................12

Pereira & Adams             Standards Track                     [Page 1]
RFC 2451             ESP CBC-Mode Cipher Algorithms        November 1998

   8. Full Copyright Statement......................................14

1. Introduction

   The Encapsulating Security Payload (ESP) [Kent98] provides
   confidentiality for IP datagrams by encrypting the payload data to be
   protected.  This specification describes the ESP use of CBC-mode
   cipher algorithms.

   While this document does not describe the use of the default cipher
   algorithm DES, the reader should be familiar with that document.
   [Madson98]

   It is assumed that the reader is familiar with the terms and concepts
   described in the "Security Architecture for the Internet Protocol"
   [Atkinson95], "IP Security Document Roadmap" [Thayer97], and "IP
   Encapsulating Security Payload (ESP)" [Kent98] documents.

   Furthermore, this document is a companion to [Kent98] and MUST be
   read in its context.

1.1 Specification of Requirements

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
   and "MAY" that appear in this document are to be interpreted as
   described in [Bradner97].

1.2 Intellectual Property Rights Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementers or users of this specification can
   be obtained from the IETF Secretariat.

2. Cipher Algorithms

   All symmetric block cipher algorithms share common characteristics
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