[121553] in cryptography@c2.net mail archive
Re: Cruising the stacks and finding stuff
daemon@ATHENA.MIT.EDU (Sandy Harris)
Thu Apr 24 17:52:52 2008
Date: Thu, 24 Apr 2008 07:22:45 +0800
From: "Sandy Harris" <sandyinchina@gmail.com>
To: Cryptography <cryptography@metzdowd.com>
In-Reply-To: <20080423161803.GC28359@randombit.net>
Jack Lloyd <lloyd@randombit.net> wrote:
> Making a cipher that uses an N bit key but is only secure to 2^M
> operations with M<N is, firstly, considered broken in many circles, as
> well as being inefficient (why generate/transmit/store 512 bit keys
> when it only provides the security of a ~300 bit (or whatever) key
> used with a perfect algorithm aka ideal cipher - why not use the
> better cipher and save the bits).
Saving bits may not matter, or may not be possible. For example,
if you are ealing with a hybrid system -- say, using RSA to transmit
the symmetric cipher key or Diffie-Hellamn to construct it -- then for
any symmetric cipher key size less than the public key size, your
overheads are the same.
--
Sandy Harris,
Nanjing, China
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