This book constitutes the refereed proceedings of the 11th International Workshop on Practice and Theory in Public-Key Cryptography, PKC 2008, held in Barcelona, Spain, in March 2008.The 21 revised full papers presented together with 1 invited lecture were carefully reviewed and selected from 71 submissions. The papers are organized in topical sections on algebraic and number theoretical cryptoanalysis, theory of public key encryption, digital signatures, identification, broadcast and key agreement, implementation of fast arithmetic, and public key encryption.