RFC 2085 (rfc2085) - Page 1 of 6

HMAC-MD5 IP Authentication with Replay Prevention

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Network Working Group                                         M. Oehler
Request for Comments: 2085                                          NSA
Category: Standards Track                                      R. Glenn
                                                                   NIST
                                                          February 1997


           HMAC-MD5 IP Authentication with Replay Prevention

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.

Abstract

   This document describes a keyed-MD5 transform to be used in
   conjunction with the IP Authentication Header [RFC-1826]. The
   particular transform is based on [HMAC-MD5].  An option is also
   specified to guard against replay attacks.

Table of Contents

   1.  Introduction...................................................1
   1.1    Terminology.................................................2
   1.2    Keys........................................................2
   1.3    Data Size...................................................3
   2.  Packet Format..................................................3
   2.1    Replay Prevention...........................................4
   2.2    Authentication Data Calculation.............................4
   3.  Security Considerations........................................5
   Acknowledgments....................................................5
   References.........................................................6
   Authors' Addresses.................................................6

1. Introduction

   The Authentication Header (AH) [RFC-1826] provides integrity and
   authentication for IP datagrams. The transform specified in this
   document uses a keyed-MD5 mechanism [HMAC-MD5].  The mechanism uses
   the (key-less) MD5 hash function [RFC-1321] which produces a message
   digest. When combined with an AH Key, authentication data is
   produced. This value is placed in the Authentication Data field of
   the AH [RFC-1826]. This value is also the basis for the data
   integrity service offered by the AH protocol.



Oehler & Glenn              Standards Track
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