HTTP/1.1 200 OK Date: Tue, 09 Apr 2002 10:08:46 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Wed, 18 Jan 1995 23:00:00 GMT ETag: "361a7e-2329-2f1d9d70" Accept-Ranges: bytes Content-Length: 9001 Connection: close Content-Type: text/plain Network Working Group P Metzger Internet Draft W A Simpson expires in six months January 1995 Authentication with Keyed MD5 draft-metzger-ah-md5-00.txt Status of this Memo This document is a submission to the IP Security Working Group of the Internet Engineering Task Force (IETF). Comments should be submitted to the ipsec@ans.net mailing list. Distribution of this memo is unlimited. This document is an Internet-Draft. 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 not appropriate to use Internet Drafts as reference material, or to cite them other than as a ``working draft'' or ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the internet-drafts Shadow Directories on: ftp.is.co.za (Africa) nic.nordu.net (Europe) ds.internic.net (US East Coast) ftp.isi.edu (US West Coast) munnari.oz.au (Pacific Rim) Abstract This document describes the use of MD5 with the IPv4 Authentication Header. Troublemakers expires in six months [Page 1] DRAFT AH MD5 January 1995 1. Introduction The Authentication Header (AH) [RAah] provides integrity and authentication for IP datagrams. This specification describes the AH use of Message Digest 5 (MD5) [RFC-1321]. A 128-bit digest is calculated over the invariant portions of the entire IP datagram and the result is included in the Authentication Data field of the Authentication Header. Implementations that claim conformance or compliance with the Authentication Header specification MUST implement the MD5 mechanism. Implementors should consult the most recent version of the IAB Standards [RFC-1610] for further guidance on the status of this document. 1.1. Keys The secret authentication key shared between the communicating parties MUST be 128 bits long. The key SHOULD be a pseudo-random number, not a guessable string of any sort. 1.2. Data Size Because MD5's 128-bit output is naturally 64-bit aligned, there is no wasted space in the Authentication Data field. 1.3. Performance MD5 reportedly has a throughput of about 60 Mbps on a fast 64-bit RISC processor with slightly tuned MD5 code [Touch94]. Nota Bene: This is possibly too slow to be used for a long period of time. Suggestions are sought on alternative authentication algorithms that would be acceptable to the IETF, have significantly faster throughput, are not patent-encumbered, and still retain adequate cryptographic strength. Troublemakers expires in six months [Page 1] DRAFT AH MD5 January 1995 2. Calculation The 128-bit digest is calculated as described in [RFC-1321]. The specification of MD5 includes a portable 'C' programming language description of the MD5 algorithm. The "b-bit message" shall consist of the 128-bit secret authentication key concatenated with (followed by) the entire IP datagram. All IP headers and payloads that are present MUST be included in the computation, with header fields whose value varies in transit (such as Hop Count) being assumed to contain zeros for the purpose of the authentication calculation. Also, the Authentication Data field of the Authentication Header is considered to contain all zeros. Security Considerations Users need to understand that the quality of the security provided by this specification depends completely on the strength of the MD5 hash function, the correctness of that algorithm's implementation, the security of the key management mechanism and its implementation, the strength of the key [CN94], and upon the correctness of the implementations in all of the participating systems. At the time of writing of this document, it is known to be possible to produce collisions in the compression function of MD5 [BdB93]. There is not yet a known method to exploit these collisions to attack MD5 in practice, but this fact is disturbing to some authors [Schneier94]. It has also recently been determined [OW94] that it is possible to build a machine for $10 Million that could find messages that hash to an arbitrary given MD5 hash. This attack requires approximately 24 days. Although this is not a substantial weakness for most IP security applications, it should be recognized that current technology is catching up to the 128 bit hash length used by MD5. Applications requiring extremely high levels of security may wish to move in the near future to algorithms with longer hash lengths. Acknowledgements The original text of this specification was derived from work by Ran Atkinson for the SIP, SIPP, and IPv6 Working Groups. Troublemakers expires in six months [Page 2] DRAFT AH MD5 January 1995 The use of MD5 for authentication is closely modeled on the work done for SNMPv2 [RFC-1446]. References [CN94] John M. Carroll & Sri Nudiati, "On Weak Keys and Weak Data: Foiling the Two Nemeses", Cryptologia, Vol. 18 No. 23 pp. 253-280, July 1994. [BdB93] B. den Boer and A. Bosselaers, "Collisions for the Compression function of MD5", Advances in Cryptology -- Eurocrypt '93 Proceedings, Berlin: Springer-Verlag 1994 [RAah] Randall Atkinson, "IPv6 Authentication Header", work in progress, 4 November 1994. [RFC-1321] Ronald Rivest, MD5 Digest Algorithm, RFC-1321, DDN Network Information Center, April 1992. [RFC-1446] James Galvin & Keith McCloghrie, Security Protocols for version 2 of the Simple Network Management Protocol (SNMPv2), RFC-1446, DDN Network Information Center, April 1993. [RFC-1610] Postel, J., "Internet Official Protocol Standards", STD 1, RFC 1610, USC/Information Sciences Institute, July 1994. [RFC-1700] Reynolds, J., and Postel, J., "Assigned Numbers", STD 2, RFC 1700, USC/Information Sciences Institute, October 1994. [OW94] Paul C. van Oorschot & Michael J. Wiener, Unpublished Crypto '94 Rump Session. [Schneier94] Schneier, B., "Applied Cryptography", John Wiley & Sons, New York, NY, 1994. ISBN 0-471-59756-2 [Touch94] Touch, J., "Report on MD5 Performance", work in progress, December 1994. Troublemakers expires in six months [Page 3] DRAFT AH MD5 January 1995 Author's Address Questions about this memo can also be directed to: Randall Atkinson Information Technology Division Naval Research Laboratory Washington, DC 20375-5320 USA Telephone: (DSN) 354-8590 Fax: (DSN) 354-7942 Perry Metzger Piermont Information Systems Inc. 160 Cabrini Blvd., Suite #2 New York, NY 10033 perry@piermont.com William Allen Simpson Daydreamer Computer Systems Consulting Services 1384 Fontaine Madison Heights, Michigan 48071 Bill.Simpson@um.cc.umich.edu bsimpson@MorningStar.com Troublemakers expires in six months [Page 4] DRAFT AH MD5 January 1995 Table of Contents 1. Introduction .......................................... 1 1.1 Keys ............................................ 1 1.2 Data Size ....................................... 1 1.3 Performance ..................................... 1 2. Calculation ........................................... 2 SECURITY CONSIDERATIONS ...................................... 2 ACKNOWLEDGEMENTS ............................................. 2 REFERENCES ................................................... 3 AUTHOR'S ADDRESS ............................................. 4