this book constitutes the thoroughly refereed postproceedings of the 4th international conference on security in communication networks, scn 2004, held in amalfi, italy in september 2004. the 25 revised full papers presented together with an invited paper were carefully selected during two rounds of reviewing and improvement. the papers are organized in topical sections on reduction of security and primitives, digital signature schemes, anonymity and privacy, authentication and identification, zero knowledge, public key cryptosystems, distributed cryptography, cryptanalysis of public key crypto systems, cryptanalysis, email security, and key distribution and feedback shift registers.