IP Encapsulating Security Payload (ESP)
RFC 2406

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Network Working Group                                            S. Kent
Request for Comments: 2406                                      BBN Corp
Obsoletes: 1827                                              R. Atkinson
Category: Standards Track                                  @Home Network
                                                           November 1998

                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 (1998).  All Rights Reserved.

Table of Contents

   1. Introduction..................................................2
   2. Encapsulating Security Payload Packet Format..................3
      2.1  Security Parameters Index................................4
      2.2  Sequence Number .........................................4
      2.3  Payload Data.............................................5
      2.4  Padding (for Encryption).................................5
      2.5  Pad Length...............................................7
      2.6  Next Header..............................................7
      2.7  Authentication Data......................................7
   3. Encapsulating Security Protocol Processing....................7
      3.1  ESP Header Location......................................7
      3.2  Algorithms..............................................10
         3.2.1  Encryption Algorithms..............................10
         3.2.2  Authentication Algorithms..........................10
      3.3  Outbound Packet Processing..............................10
         3.3.1  Security Association Lookup........................11
         3.3.2  Packet Encryption..................................11
         3.3.3  Sequence Number Generation.........................12
         3.3.4  Integrity Check Value Calculation..................12
         3.3.5  Fragmentation......................................13
      3.4  Inbound Packet Processing...............................13
         3.4.1  Reassembly.........................................13
         3.4.2  Security Association Lookup........................13
         3.4.3  Sequence Number Verification.......................14
         3.4.4  Integrity Check Value Verification.................15

Kent & Atkinson             Standards Track                     [Page 1]
RFC 2406           IP Encapsulating Security Payload       November 1998

         3.4.5  Packet Decryption..................................16
   4. Auditing.....................................................17
   5. Conformance Requirements.....................................18
   6. Security Considerations......................................18
   7. Differences from RFC 1827....................................18
   Acknowledgements................................................19
   References......................................................19
   Disclaimer......................................................20
   Author Information..............................................21
   Full Copyright Statement........................................22

1.  Introduction

   The Encapsulating Security Payload (ESP) header is designed to
   provide a mix of security services in IPv4 and IPv6.  ESP may be
   applied alone, in combination with the IP Authentication Header (AH)
   [KA97b], or in a nested fashion, e.g., through the use of tunnel mode
   (see "Security Architecture for the Internet Protocol" [KA97a],
   hereafter referred to as the Security Architecture document).
   Security services can be provided between a pair of communicating
   hosts, between a pair of communicating security gateways, or between
   a security gateway and a host.  For more details on how to use ESP
   and AH in various network environments, see the Security Architecture
   document [KA97a].

   The ESP header is inserted after the IP header and before the upper
   layer protocol header (transport mode) or before  an encapsulated IP
   header (tunnel mode).  These modes are described in more detail
   below.

   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.  The
   set of services provided depends on options selected at the time of
   Security Association establishment and on the placement of the
   implementation.  Confidentiality may be selected independent of all
   other services.  However, use of confidentiality without
   integrity/authentication (either in ESP or separately in AH) may