-----BEGIN PGP SIGNED MESSAGE----- Bill Stewart writes:

Are there any simple but crypto-strong hash functions? [...] I was thinking about using RC4 in some feedback mode as a MAC, but it sounds like that's not secure enough? Is there anything else that's short? MD5 requires too much code.

Phil Rogaway gave a great talk at RSADSC about keyed hashing MACs. In all he described 12 different MACs (some of them variations on a theme), and gave some efficiency/security tradeoff numbers relative to the security of the underlying hash function. Apparently he had a paper in Crypto `95 about bucket hashing, which is generally fast and simple and apparently pretty secure. The idea is to place each word of the message into a unique fixed-size subset of a large set of buckets, XOR each bucket internally, then concatenate the results. I haven't yet read the paper (though I expect to do so soon), so I don't know all the details. I think the notion is that you can plug in any pseudo-random function to select the buckets, and get provably good security if you know your function is suitably pseudo-random. Check: http://wwwcsif.cs.ucdavis.edu/~rogaway/talks/list.html which has a link to his slides from last week, and http://wwwcsif.cs.ucdavis.edu/~rogaway/papers/list.html which has links to a heap of papers, including the full version of the Crypto `95 bucket hashing one. Futplex <futplex@pseudonym.com> "a heap of PS papers that I _can_ print out without destroying whole forests" -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQEVAwUBMQiouCnaAKQPVHDZAQHo+Af7BtpL5kErtzeWR0dBuR1/rOfQzw8Ezaxi Gp7Va8kjJLYJlWa1+Ih2fbKr8oUIKL1N1a5JoDarr2G75B9GilyyjCIf75FIrWnZ JQDti8wJIK6TGV9ClZGbl6jowUkc4PtFzp6VN85K/Rnv/l/Wekv4kWl41O2Cq656 bsQaE2jYAfRqkOziarytaszVROoTNbGvyYoLk1ESf9yijwp0E9R/SXlw4OvUAna7 qSnuhbIayLX8auQWxoUf9lRlJ8tdreqXzP2G4yL1tXI+i+nr6z3A9m/+sXXCxNb1 vzQtUTkVtCniKoGrtm7WN0RtusjIrVEoaDi/msx+ADBphHGxPxIJlA== =g1Jt -----END PGP SIGNATURE-----