RFC 3230 (rfc3230) - Page 1 of 13

Instance Digests in HTTP

Network Working Group                                           J. Mogul
Request for Comments: 3230                                    Compaq WRL
Category: Standards Track                                    A. Van Hoff
                                                                 Marimba
                                                            January 2002


                        Instance Digests in HTTP

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 (2002).  All Rights Reserved.

Abstract

   HTTP/1.1 defines a Content-MD5 header that allows a server to include
   a digest of the response body.  However, this is specifically defined
   to cover the body of the actual message, not the contents of the full
   file (which might be quite different, if the response is a Content-
   Range, or uses a delta encoding).  Also, the Content-MD5 is limited
   to one specific digest algorithm; other algorithms, such as SHA-1
   (Secure Hash Standard), may be more appropriate in some
   circumstances.  Finally, HTTP/1.1 provides no explicit mechanism by
   which a client may request a digest.  This document proposes HTTP
   extensions that solve these problems.

Table of Contents

   1 Introduction....................................................  2
        1.1 Other limitations of HTTP/1.1............................  3
   2 Goals...........................................................  4
   3 Terminology.....................................................  5
   4 Specification...................................................  6
        4.1 Protocol parameter specifications........................  6
             4.1.1 Digest algorithms.................................  6
        4.2 Instance digests.........................................  7
        4.3 Header specifications....................................  8
             4.3.1 Want-Digest.......................................  8
             4.3.2 Digest............................................  9
   5 Negotiation of Content-MD5......................................  9



Mogul, et. al.              Standards Track