In article <9308201639.AA10388@newton.apple.com>, : Well, since I'm here, I thought I'd satisfy a curiosity of mine. : Has anyone done any research, formal or informal, on the use of : genetic algorithms to break cyphers? If not, would anyone care to : discuss how it might be done? : : GA's (which I love, but you won't be able to tell from the following) are a : 'robust' search mechanism better at finding _good_ answers than _the_ : answer. Right. So the essential problem is to define "good" in the context of deciphering. I'm sitting here trying to visualize a structure (>3 dimensions always have eluded me :-) that would let one do this but actually, I had something quite a bit more mundane in mind. What about the simple GA where each of half the bit string represents a number and the fitness function is the bit count of the complement of the XOR of the product of the two numbers and a (presumably) composite number? This seems like it would have the sorts of properties that makee GAs work and, if it this resulted in a practicable factoring system, would make hash out of several cryptosystems. : However, in simple substitution ciphers, frequencies and patterns in : partial decryptions can provide the reward GA's need to climb the hills. Right. I'd assume you'd generate a key and then compute the fitness frorm the decrypted text's statistics. That's an easy one. :-)