Book excerpt: This book constitutes the refereed proceedings of the 25th Annual International Conference on the Theory and Applications of Cryptographic Techniques, EUROCRYPT 2006. 33 revised full papers are presented together with 2 invited talks. The papers are organized in topical sections on cryptanalysis, cryptography meets humans, stream ciphers, hash functions, oblivious transfer, numbers and lattices, foundations, block ciphers, cryptography without random oracles, multiparty computation, and cryptography for groups.