On Fri, Nov 14, 2003 at 09:19:25AM +0100, martin f krafft wrote: > it came up lately in a discussion, and I couldn't put a name to it: > a means to use symmetric crypto without exchanging keys: > > - Alice encrypts M with key A and sends it to Bob > - Bob encrypts A(M) with key B and sends it to Alice > - Alice decrypts B(A(M)) with key A, leaving B(M), sends it to Bob > - Bob decrypts B(M) with key B leaving him with M. > > Are there algorithms for this already? What's the scheme called?
"Stupid crypto", probably. Unless I'm missing something, this only works if A(A(M)) = M. Symetric crypto, not just symetric keys. NEVER willingly give the cryptanalyst the same message encrypted with the same system using two different keys. For the simple case, suppose F(X) = X ^ S (exclusive or with a string generated from the key). Then M = A(M) ^ B(M) ^ B(A(M)), right? Probably something similar for other symetric systems. -- [EMAIL PROTECTED] --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]
