Gustavus J. Simmons (born 1930) is a retired cryptographer and former manager of the applied mathematics Department and Senior Fellow at Sandia National Laboratories. He has worked primarily with authentication theory, developing cryptographic techniques for solving problems of mutual distrust and in devising protocols whose function can be trusted, even though some of the inputs or participants cannot be. Simmons was born in West Virginia and was named after his grandfather, a prohibition officer who was gunned down three years before Gustavus was born. He began his post-secondary education at Deep Springs College, and received his Ph.D in mathematics from the University of New Mexico, Albuquerque.
Simmons has published over 170 papers, many of which are devoted to asymmetric encryption techniques. His technical contributions include the development of subliminal channels which make it possible to conceal covert communications in digital signatures and the mathematical formulation of an authentication channel paralleling in many respects the secrecy channel formulated by Claude Shannon in 1948. In the 1980s, he helped form the International Association for Cryptologic Research (IACR). He is also the creator of the Ramsey/graph theory-based mathematical game Sim.
At Sandia, Simmons was primarily involved in the command and control of nuclear weapons, in using authentication to make possible the verification of compliance with arms control treaties, and in the cryptographic aspects of verifying adherence to the Comprehensive Test Ban Treaty for nuclear weapons. In a review of Contemporary Cryptology (see publications), Don Coppersmith summarized the problem: