This book constitutes the refereed proceedings of the 4th Western European Workshop on Research in Cryptology, WEWoRC 2011, held in Weimar Germany, in July 2011. The 10 revised full papers were carefully reviewed and selected from numerour submissions. The papers span a wide spectrum of topics from foundations of cryptology, upto secret-key cryptosystems and hash functions, public-key cryptosystems, modes of operation, cryptographic protocols, hardware and software implementation of cryptosystems and their integration into secure systems, and applications such as watermarking and code...