> Hi, > > I realise this is slightly OT for the list, but there'll be a lot of people > on this list with experience in cryptography, so here's as good a place as > any to ask this ;). > Does anyone know of a cipher that meets the following two requirements: > - You cannot determine the key from the encrypted & decrypted text (by key I > mean the 'session' key)
Any secure cipher would qualify (unless you're describing a known-plaintext attack). > - You can decrypt in a 'nested' fashion - eg, if E(M,x) means encrypting M > with key x and D(M,x) means decrypt M with key x, then the algorithm should > satisfy D(E(E(M,a),b),a) == E(M,b) I doubt such a thing is possible. Of course, we need the mathmatical proof to be sure. In any case, what's wrong with the public key crypto? Sure it's slow, but you only do it once. > > What I'm thinking (and I'm sure I've come across this before) is that you > could exchange secret keys with someone sans public-key crypto by doing the > following (Where M is the private key/message to be exchanged): > Alice sends E(M, a) to Bob > Bob sends E(E(M, a), b) back to Alice > Alice decrypts the result: D(E(E(M, a), b), a) to get E(M, b) and sends this > to Bob > Bob decrypts E(M, b) to get M. > > Anyone know of a cipher that could do that, or if it's possible at all? > > Sorry for the OTness, > > Nick Johnson > > > _______________________________________________ > freenet-tech mailing list > [EMAIL PROTECTED] > http://lists.freenetproject.org/mailman/listinfo/tech > _______________________________________________ freenet-tech mailing list [EMAIL PROTECTED] http://lists.freenetproject.org/mailman/listinfo/tech
