-----BEGIN PGP SIGNED MESSAGE-----

Date: Fri, 10 Nov 1995 11:52:41 -0800 From: Bill Stewart <stewarts@ix.netcom.com> Subject: Re: coding and nnet's

Schneier's 2nd edition says "Neural nets aren't terribly useful for cryptography, primarily because of the shape of the solution space.

Neural nets work best for problems that have a continuity of solutions, some better than others. This allows a neural net to learn, proposing better and better solutions as it does. Breaking an algorithm provides for very little in the way of learning opportunities: You either recover the key or you don't. (At least this is true if the algorithm is any good.)

Has anyone tried using neural nets or similar techniques for searching for useful nonrandom properties of the round functions of block ciphers or hash functions? This might be useful in trying to prepare some new kind of attack, find a balanced binary function that is useful in using the generalization of linear cryptanalysis discussed by Harpes, Kramer, and Massey at Eurocrypt '95, find a better "difference" function for use in a differential attack, etc.

Neural nets work well in structured environments when there is something to learn, but not in the high-entropy, seemingly random world of cryptography." And he doesn't give any references.

Merkle's paper on Khufu and Khafre addresses this idea, I think. Merkle comments that it's not going to be useful against a full cipher, but that it might be useful against (say) Khufu with one or two octets.

# Thanks; Bill # Bill Stewart, Freelance Information Architect, stewarts@ix.netcom.com # Phone +1-510-247-0663 Pager/Voicemail 1-408-787-1281

Note: Please respond via e-mail as well as or instead of posting, as I get CP-LITE instead of the whole list. --John Kelsey, jmkelsey@delphi.com PGP 2.6 fingerprint = 4FE2 F421 100F BB0A 03D1 FE06 A435 7E36 -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBMKhv1UHx57Ag8goBAQE5IAQAtV3GTqZO08WwHDJSI3Dj2NgIu7rQPrUH V5vBCWTCvRsVNt07K8FbKMxPhF+QmXINPlOEMn4qZbhph0oyf/zAj3uV+6yzO3Eg FMXrZzc1zOOdcfp9IcMvoXvd/av9zq/jH6Sn6yZB3jTO42ENeSSLNbxtaBrzgABl zPklYWOnDrw= =x3kP -----END PGP SIGNATURE-----