Bailey Whitfield 'Whit' Diffie (born June 5, 1944) is an American cryptographer and one of the pioneers of public-key cryptography.

Diffie and Martin Hellman's paper "New Directions in Cryptography" was published in 1976. It introduced a radically new method of distributing cryptographic keys, that went far toward solving one of the fundamental problems of cryptography, key distribution. It has become known as Diffie–Hellman key exchange. The article also seems to have stimulated the almost immediate public development of a new class of encryption algorithms, the asymmetric key algorithms.