This book constitutes the refereed proceedings of the 23rd Annual International Cryptology Conference, CRYPTO 2003, held in Santa Barbara, California in August 2003. The 34 revised full papers presented together with 2 invited papers were carefully reviewed and selected from 166 submissions. The papers are organized in topical sections on public key cryptanalysis, alternate adversary models, protocols, symmetric key cryptanalysis, universal composability, zero knowledge, algebraic geometry, public key constructions, new problems, symmetric key constructions, and new models.