In article <199501120502.VAA29808@largo.remailer.net>, Eric Hughes <eric@remailer.net> wrote:

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From: cactus@seabsd.hks.net (L. Todd Masco) (bunch of stuff deleted)

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I guess this reduces to: do strong cyphers have "signatures" of some sort, by which the type of encryption can be derived?

If they do, they're likely not _strong_ ciphers.

Great... that's the answer I was looking for, and what my gut feeling was. I'm trying to determine how much rope is too much for a first pass.

Related: is there, in general or in any known specific cases, any loss of security in using sym. cipher A on ciphertext B (of another sym. cipher) with the same key? With different keys (I would think not, but I vaguely remember mention of something here long ago)?

Is this asking the question, "Does DES form a group with IDEA?" (Substitute your favorite cipher.) Since it took about 15 years to figure out DES is _not_ a group, I suspect it will take a long time to figure out the answer to that question for each pair of ciphers you're going to substitute. Seems to me it's a good basic idea. If it costs, for example, a million bucks to crack a cipher; you have three ciphers that can be used; then the best-case cost to crack a message just tripled! Of course, if you choose two ciphers stronger than DES, it probably went up a little more (g). If the ciphers don't form a group, you just made your system unbreakable. Just use two ciphers. Then a brute-force attacker has to check each key for each cipher once when it is applied first, and once for each of the possible keys for the other cipher when it is applied second! Sounds too good to be true. Am I missing something? Pat