Advances in Cryptology – EUROCRYPT 2012 : 31st Annual International Conference on the Theory and Applications of Cryptographic Techniques Cambridge UK April 15 19 2012. Proceedings This book constitutes the refereed proceedings of the 31st Annual International Conference on the Theory and Applications of Cryptographic Techniques EUROCRYPT 2012 held in Cambgridge UK in April 2012. The 41 papers presented together with 2 invited talks were carefully reviewed and selected from 195 submissions. The papers are organized in topical sections on index calculus symmetric constructions secure computation protocols lossy trapdoor functions tools symmetric cryptanalysis fully homomorphic encryption asymmetric cryptanalysis efficient reductions public key schemes security models and lattices.