Re: extracting two different plain texts with two different keys

Scott wrote:
I wonder if anyone know of a good cipher that allows you to encrypt two
different plain texts into one cyphertext so that if you have one key
you get one plain text and if you have the second key you get the
second text.

I know that this class of Algorithms exist but I can't for the life of
me remember what there called. Or how secure they are.

Note that if we had a bijective compression function from the set of plausible plaintexts to bitstrings of a specified length, what you ask for would be easy. You'd compress the message, encrypt the bitstring (using, say, a stream cipher without authentication) and the resulting ciphertext could be decrypted with any other key to something that would decompress into a different plausible plaintext.
It's possible to come up with such a compression function by suitably restricting the syntax and vocabulary of messages. E.g., if the set of plausible plaintexts is {"yes", "no"}, it's trivial.

--Mike Amling
.

Loading