Multiple symetric cyphers

[cactus@seabsd.hks.net (L. Todd Masco)]

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One of the possible weaknesses in public-key messages is their dependence
upon a particular symetric cypher for the message with the session key
being contained in the block encrypted by the antisymetric cypher.  IE,
if a weakness in IDEA is discovered, it can be exploited against all PGP
messages.

I'm wondering: would the strength be increased by using a randomly selected
symetric cypher?  IE, as PGP uses IDEA and RIPEM uses DES/3DES, what if a
random cypher were selected from a set of cryptographically strong
symetric cyphers and information about the cypher selected were encrypted
in the RSA-encrypted block?

I guess this reduces to: do strong cyphers have "signatures" of some sort,
by which the type of encryption can be derived?  And if so, can this
"signature" be reduced by including part (eg, the first and last bytes)
of the ciphertext in the RSA block rather than the "clear" cyphertext block?

Just a thought,
- - --
Todd Masco     | "life without caution/ the only worth living / love for a man/
cactus@hks.net |  love for a woman/ love for the facts/ protectless" - A Rich
<a href="http://www.hks.net/~cactus/cactus.html">Cactus' Homepage</a>

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