IP Encapsulating Security Payload (ESP)
RFC 4303

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Network Working Group                                            S. Kent
Request for Comments: 4303                              BBN Technologies
Obsoletes: 2406                                            December 2005
Category: Standards Track

                IP Encapsulating Security Payload (ESP)

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

   This document describes an updated version of the Encapsulating
   Security Payload (ESP) protocol, which is designed to provide a mix
   of security services in IPv4 and IPv6.  ESP is used to provide
   confidentiality, data origin authentication, connectionless
   integrity, an anti-replay service (a form of partial sequence
   integrity), and limited traffic flow confidentiality.  This document
   obsoletes RFC 2406 (November 1998).

Table of Contents

   1. Introduction ....................................................3
   2. Encapsulating Security Payload Packet Format ....................5
      2.1. Security Parameters Index (SPI) ...........................10
      2.2. Sequence Number ...........................................12
           2.2.1. Extended (64-bit) Sequence Number ..................12
      2.3. Payload Data ..............................................13
      2.4. Padding (for Encryption) ..................................14
      2.5. Pad Length ................................................15
      2.6. Next Header ...............................................16
      2.7. Traffic Flow Confidentiality (TFC) Padding ................17
      2.8. Integrity Check Value (ICV) ...............................17
   3. Encapsulating Security Protocol Processing .....................18
      3.1. ESP Header Location .......................................18
           3.1.1. Transport Mode Processing ..........................18
           3.1.2. Tunnel Mode Processing .............................19

Kent                        Standards Track                     [Page 1]
RFC 4303        IP Encapsulating Security Payload (ESP)    December 2005

      3.2. Algorithms ................................................20
           3.2.1. Encryption Algorithms ..............................21
           3.2.2. Integrity Algorithms ...............................21
           3.2.3. Combined Mode Algorithms ...........................22
      3.3. Outbound Packet Processing ................................22
           3.3.1. Security Association Lookup ........................22
           3.3.2. Packet Encryption and Integrity Check Value
                  (ICV) Calculation ..................................22
                  3.3.2.1. Separate Confidentiality and
                           Integrity Algorithms ......................23
                  3.3.2.2. Combined Confidentiality and
                           Integrity Algorithms ......................24
           3.3.3. Sequence Number Generation .........................25
           3.3.4. Fragmentation ......................................26
      3.4. Inbound Packet Processing .................................27
           3.4.1. Reassembly .........................................27
           3.4.2. Security Association Lookup ........................27
           3.4.3. Sequence Number Verification .......................28
           3.4.4. Integrity Check Value Verification .................30
                  3.4.4.1. Separate Confidentiality and
                           Integrity Algorithms ......................30
                  3.4.4.2. Combined Confidentiality and
                           Integrity Algorithms ......................32
   4. Auditing .......................................................33
   5. Conformance Requirements .......................................34
   6. Security Considerations ........................................34
   7. Differences from RFC 2406 ......................................34
   8. Backward-Compatibility Considerations ..........................35
   9. Acknowledgements ...............................................36
   10. References ....................................................36
      10.1. Normative References .....................................36
      10.2. Informative References ...................................37
   Appendix A: Extended (64-bit) Sequence Numbers ....................38
      A1. Overview ...................................................38
      A2. Anti-Replay Window .........................................38
          A2.1. Managing and Using the Anti-Replay Window ............39