Computer scientist and cryptographer.
With Jim Reeds founded the Voynich Manuscript Mailing List in 1991.
He is best known for his work solving or debunking some of the world's most famous unsolved codes. In 1980 he wrote a paper debunking the Beale Ciphers, and he received international media attention for being the first person to publicly solve parts 1-3 on the CIA's Kryptos sculpture in 1999. On the PBS website, they report that he has been called "arguably the best non-government cryptanalyst in the U.S." in the field of classical (historical) cryptosystems.
His page on Wikipedia, including a list of writings, is [1], and on Chess Programming Wiki [2].
A list of his publications here and here. A WordPress article here.