This book constitutes the refereed proceedings of the 15th International Conference on Practice and Theory in Public Key Cryptography PKC 2012 held in Darmstadt Germany in May 2012. The 41 papers presented were carefully reviewed and selected from 188 submissions. The book also contains one invited talk. The papers are organized in the following topical sections: homomorphic encryption and LWE signature schemes code-based and multivariate crypto public key encryption: special properties identity-based encryption public-key encryption: constructions secure two-party and multi-party computations key exchange and secure sessions public-key encryption: relationships DL DDH and more number theory and beyond ordinary signature schemes.