Network Working Group S. Hollenbeck Internet-Draft VeriSign, Inc. Expires: March 6, 2003 September 5, 2002 Transport Layer Security Protocol Compression Methods draft-ietf-tls-compression-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on March 6, 2003. Copyright Notice Copyright (C) The Internet Society (2002). 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, CompressionMethod.null, which specifies that data exchanged via the record protocol will not be compressed. This document describes additional compression methods associated with lossless data compression algorithms for use with TLS. Conventions Used In This Document Hollenbeck Expires March 6, 2003 [Page 1] Internet-Draft TLS Compression Methods September 2002 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]. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Compression Methods . . . . . . . . . . . . . . . . . . . . . 4 3. Intellectual Property Considerations . . . . . . . . . . . . . 5 4. Internationalization Considerations . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 Normative References . . . . . . . . . . . . . . . . . . . . . 10 Informative References . . . . . . . . . . . . . . . . . . . . 11 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 11 Full Copyright Statement . . . . . . . . . . . . . . . . . . . 12 Hollenbeck Expires March 6, 2003 [Page 2] Internet-Draft TLS Compression Methods September 2002 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 additional compression methods associated with lossless data compression algorithms for use with TLS. Standardization of the compressed data formats and compression algorithms associated with the compression methods is beyond the scope of this document. Hollenbeck Expires March 6, 2003 [Page 3] Internet-Draft TLS Compression Methods September 2002 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; 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: 1. Values from 0 (zero) through 63 decimal (0x3F) inclusive are reserved for future standardization efforts of the IETF TLS working group. 2. Values from 64 decimal (0x40) through 192 decimal (0xC0) are reserved for assignment by the IANA for specifications developed outside the TLS working group. Assignments from this range of values MUST be made by the IANA and MUST be associated with a formal reference that describes the compression method. 3. Values from 193 decimal (0xC1) through 255 decimal (0xFF) are reserved for private use. Additional information describing the role of the IANA in the allocation of compression method identifiers is described in Section 5. In addition, this definition is updated to include assignment of three additional compression methods: enum { null(0), ZLIB(1), LZS(2), RLE(3), (255) } CompressionMethod; The ZLIB compression method is described in RFC 1950 [5]. The Lempel Zif Stac (LZS) compression method is described in ANSI publication X3-241 [6]. The Run Length Encoding (RLE) compression method is described in part 5 of the Digital Imaging and Communications in Medicine standard [7]. Hollenbeck Expires March 6, 2003 [Page 4] Internet-Draft TLS Compression Methods September 2002 3. Intellectual Property Considerations Many compression algorithms are subject to patent or other intellectual property rights claims. Implementers are encouraged to seek legal guidance to better understand the implications of developing implementations of the compression methods described in this document. Hollenbeck Expires March 6, 2003 [Page 5] Internet-Draft TLS Compression Methods September 2002 4. Internationalization Considerations The compression method identifiers specified in this document are machine-readable numbers. As such, issues of human internationalization and localization are not introduced. Hollenbeck Expires March 6, 2003 [Page 6] Internet-Draft TLS Compression Methods September 2002 5. IANA Considerations This document does not have a direct impact on the IANA, but it does define ranges of compression method values for future assignment. Values from the range reserved for future standardization efforts of the TLS working group MUST be assigned according to the "Standards Action" policy described in RFC 2434 [3]. Values from the range reserved for private use MUST be used according to the "Private Use" policy described in RFC 2434. Values from the general IANA pool MUST be assigned according to the "IETF Consensus" policy described in RFC 2434. Hollenbeck Expires March 6, 2003 [Page 7] Internet-Draft TLS Compression Methods September 2002 6. Security Considerations This document does not introduce any topics that alter the threat model addressed by TLS. However, data compression prior to encryption can potentially provide a security benefit in "flattening" the distribution of unencrypted octets (or increasing the unicity distance) by using fewer bits to represent common characters. In situations where the unencrypted octets represent human-readable text, reducing the predictability of text patterns can make it slightly more difficult to mount a successful attack on the encrypted octets. Hollenbeck Expires March 6, 2003 [Page 8] Internet-Draft TLS Compression Methods September 2002 7. Acknowledgements The concepts described in this document were originally discussed on the IETF TLS working group mailing list in December, 2000. The author acknowledges the contributions to that discussion provided by Jeffrey Altman, Eric Rescorla, and Marc Van Heyningen. Hollenbeck Expires March 6, 2003 [Page 9] Internet-Draft TLS Compression Methods September 2002 Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A. and P. Kocher, "The TLS Protocol Version 1.0", RFC 2246, January 1999. [3] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. Hollenbeck Expires March 6, 2003 [Page 10] Internet-Draft TLS Compression Methods September 2002 Informative References [4] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler, "Extensible Markup Language (XML) 1.0 (2nd ed)", W3C REC-xml, October 2000, . [5] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data Format Specification version 3.3", RFC 1950, May 1996. [6] American National Standards Institute, "Data Compression Method, Adaptive Coding with Sliding Window of Information Interchange", ANSI X3.241, 1994. [7] National Electrical Manufacturers Association, "Digital Imaging and Communications in Medicine (DICOM) Part 5: Data Structures and Encoding", 2001, . Author's Address Scott Hollenbeck VeriSign, Inc. 21345 Ridgetop Circle Dulles, VA 20166-6503 US EMail: shollenbeck@verisign.com Hollenbeck Expires March 6, 2003 [Page 11] Internet-Draft TLS Compression Methods September 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Hollenbeck Expires March 6, 2003 [Page 12]