IMPROVED CRYPTOGRAPHIC METHOD AND SYSTEM

摘要

A cryptographic algorithm such as AES/Rijndael involves a non- linear substitution step wherein an input byte is replaced by an output byte according to an S-box. This could be done using a look-up table. In the invention the contents of the S-box is given as input to the cryptographic method together with a cryptographic key to be used in the cryptographic method. Content can be encrypted using the chosen key and the chosen S-box as input before distribution. In a system comprising a server configured to execute the method and a plurality of clients, the clients may have the same chosen S-box or may have mutually different S-boxes.