[6950] in cryptography@c2.net mail archive
Re: key agility and IPsec
daemon@ATHENA.MIT.EDU (Ron Rivest)
Thu Apr 27 11:32:35 2000
Date: Wed, 26 Apr 2000 22:59:20 -0400 (EDT)
Message-Id: <200004270259.WAA17193@ibis.lcs.mit.edu>
From: Ron Rivest <rivest@theory.lcs.mit.edu>
To: cryptography@c2.net
In-reply-to: <200004270133.VAA01022@postal.research.att.com> (message from
Steve Bellovin on Wed, 26 Apr 2000 19:50:10 -0400)
Steve --
Don't your statistics support the argument that key agility is
*not* likely to be terribly important by itself?
With a cache capable of storing only 5 key setups, you get at least a
75% hit rate, by your statistics.
This effectively reduces key setup time by a factor of *four*, making it
really second-order compared to the bulk of the encryption work to be
done.
Depending on the algorithm, a cache for 5 key setups is pretty
minimal. For example, a setup key for RC6 requires only 176 bytes; a
kilobyte of RAM would easily do for a five-key cache.
I like your miss-rate statistics, but feel they support better the
argument that ``key agility is not terribly important by itself''
rather than the statement ``key agility is terribly important.''
Cheers,
Ron
