This volume comprises the proceedings of the 4th Conference on Advanced - cryption Standard, AES State of the Crypto Analysis, which was held in Bonn, Germany, during 10 12 May 2004. The conference followed a series of events organized by the US National - stitute of Standards and Technology (NIST) in order to hold an international competition to decide on an algorithm to serve as the Advanced Encryption Standard (AES). In 1998, at the ?rst AES conference (AES 1), 15 di?erent al- rithmswerepresented, discussed, reviewedandveri?ed.Asecondconferencewas organizedinApril1999,...