On 09/08/2013 11:49 AM, Perry E. Metzger wrote:
That said, your hypothetical seems much like "imagine that you can float by the power of your mind alone". The construction of such a cipher with a single master key that operates just like any other key seems nearly impossible, and that should be obvious.
True. A universal key that uses the same decryption operation as a normal key is clearly stupid. I guess the thing I was thinking of is that the "attacker" knows a method that allows him to decrypt anything if he knows the IV, but cannot recover the key used to encrypt it. Which is of course a public-key system, where the decryption method is the "private" key and the IV is the "public" key. The thing I was thinking of as a "key" functions as a "nonce" or subkey which allows people unrelated to the private key holder to communicate semi-privately by shared secret, but the private key is a backdoor on their communication. Duh. Sorry, just wasn't thinking of the right "parallel mapping" of what I described. For the cipher itself to function as a key sort of escaped my attention. Sorry to waste time. Ray. _______________________________________________ The cryptography mailing list firstname.lastname@example.org http://www.metzdowd.com/mailman/listinfo/cryptography