A
professor at
Cambridge (that's in
England), who has done a lot of solid work in the areas of
cryptography,
privacy (especially
medical privacy),
peer to peer systems, and
security engineering. He is currently head of the security lab in Cambridge.
Among other things, he co-designed the AES candidate Serpent (with Eli Biham and Lars Knudsen) and the hash function Tiger, with Eli Biham. He also has done some analysis work, breaking several stream ciphers, including one called Fish, which was designed by Siemens. He also discovered some attacks on several cryptocards, including a very expensive one made by IBM that is used by a lot of banks and credit card companies.
He recently wrote a very good book on security engineering, entitled "Security Engineering - a Guide to Building Dependable Distributed Systems" and of course he has plenty of research papers, most of which you can find on his web page, which is http://www.cl.cam.ac.uk/~rja14