Transport Layer Security Protocol Compression Methods
RFC 3749

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Network Working Group                                      S. Hollenbeck
Request for Comments: 3749                                VeriSign, Inc.
Category: Standards Track                                       May 2004

         Transport Layer Security Protocol Compression Methods

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 (2004).  All Rights Reserved.

Abstract

   The Transport Layer Security (TLS) protocol (RFC 2246) includes
   features to negotiate selection of a lossless data compression method
   as part of the TLS Handshake Protocol and to then apply the algorithm
   associated with the selected method as part of the TLS Record
   Protocol.  TLS defines one standard compression method which
   specifies that data exchanged via the record protocol will not be
   compressed.  This document describes an additional compression method
   associated with a lossless data compression algorithm for use with
   TLS, and it describes a method for the specification of additional
   TLS compression methods.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Compression Methods  . . . . . . . . . . . . . . . . . . . . .  2
       2.1.  DEFLATE Compression. . . . . . . . . . . . . . . . . . .  3
   3.  Compression History and Packet Processing  . . . . . . . . . .  4
   4.  Internationalization Considerations  . . . . . . . . . . . . .  4
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  4
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  5
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  6
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  6
       8.1.  Normative References . . . . . . . . . . . . . . . . . .  6
       8.2.  Informative References . . . . . . . . . . . . . . . . .  6
       Author's Address . . . . . . . . . . . . . . . . . . . . . . .  7
       Full Copyright Statement . . . . . . . . . . . . . . . . . . .  8

Hollenbeck                  Standards Track                     [Page 1]
RFC 3749                TLS Compression Methods                 May 2004

1.  Introduction

   The Transport Layer Security (TLS) protocol (RFC 2246, [2]) includes
   features to negotiate selection of a lossless data compression method
   as part of the TLS Handshake Protocol and to then apply the algorithm
   associated with the selected method as part of the TLS Record
   Protocol.  TLS defines one standard compression method,
   CompressionMethod.null, which specifies that data exchanged via the
   record protocol will not be compressed.  While this single
   compression method helps ensure that TLS implementations are
   interoperable, the lack of additional standard compression methods
   has limited the ability of implementers to develop interoperable
   implementations that include data compression.

   TLS is used extensively to secure client-server connections on the
   World Wide Web.  While these connections can often be characterized
   as short-lived and exchanging relatively small amounts of data, TLS
   is also being used in environments where connections can be long-
   lived and the amount of data exchanged can extend into thousands or
   millions of octets.  XML [4], for example, is increasingly being used
   as a data representation method on the Internet, and XML tends to be
   verbose.  Compression within TLS is one way to help reduce the
   bandwidth and latency requirements associated with exchanging large
   amounts of data while preserving the security services provided by
   TLS.

   This document describes an additional compression method associated
   with a lossless data compression algorithm for use with TLS.
   Standardization of the compressed data formats and compression
   algorithms associated with this compression method is beyond the
   scope of this document.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].

2.  Compression Methods

   TLS [2] includes the following compression method structure in
   sections 6.1 and 7.4.1.2 and Appendix sections A.4.1 and A.6:

   enum { null(0), (255) } CompressionMethod;

Hollenbeck                  Standards Track                     [Page 2]
RFC 3749                TLS Compression Methods                 May 2004

   which allows for later specification of up to 256 different
   compression methods.  This definition is updated to segregate the
   range of allowable values into three zones: