Key Management Considerations for the TCP MD5 Signature Option (RFC3562)
Original Publication Date: 2003-Jul-01
Included in the Prior Art Database: 2003-Jul-03
Internet Society Requests For Comment (RFCs)
The TCP MD5 Signature Option (RFC 2385), used predominantly by BGP, has seen significant deployment in critical areas of Internet infrastructure. The security of this option relies heavily on the quality of the keying material used to compute the MD5 signature. This document addresses the security requirements of that keying material.
Network Working Group M. Leech
Request for Comments: 3562 Nortel Networks
Category:Informational July 2003
Key Management Considerations for
the TCP MD5 Signature Option
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright (C) The Internet Society (2003). All Rights Reserved.
The TCP MD5 Signature Option (RFC 2385), used predominantly by BGP,
has seen significant deployment in critical areas of Internet
infrastructure. The security of this option relies heavily on the
quality of the keying material used to compute the MD5 signature.
This document addresses the security requirements of that keying
The security of various cryptographic functions lies both in the
strength of the functions themselves against various forms of attack,
and also, perhaps more importantly, in the keying material that is
used with them. While theoretical attacks against the simple MAC
construction used in RFC 2385 are possible [MDXMAC], the number of
text-MAC pairs required to mount a forgery make it vastly more
probable that key-guessing is the main threat against RFC 2385.
We show a quantitative approach to determining the security
requirements of keys used with [RFC2385], which tends to suggest the
o Key lengths SHOULD be between 12 and 24 bytes, with larger keys
having effectively zero additional computational costs when
compared to shorter keys.
Leech Informational [Page 1]
RFC 3562 Considerations for the TCP MD5 Signature Option July 2003
o Key sharing SHOULD be limited so that keys aren't shared among
multiple BGP peering arrangements.
o Keys SHOULD be changed at least every 90 days.
1.1. Requirements Keywords
The keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
and "MAY" that appear in this document are to be interpreted as
described in [RFC2119].
2. Performance assumptions
The most recent performance study of MD5 that this author was able to
find was undertaken by J. Touch at ISI. The results of this study
were documented in [RFC1810]. The assumption is that Moores Law
applies to the data in the study, which at the time showed a
best-possible *software* performance for MD5 of 87Mbits/second.
Projecting this number forward to the ca 2002 timeframe of this