1. A method of implementing a block cipher algorithm by a device storing a fixed initialization datum, the method comprising: performing an initialization function on the fixed initialization datum and on a state value that is specific to a session, thereby resulting in a modified initialization datum; and using the modified initialization datum, executing a first iteration of the block cipher algorithm in the course of the session to produce a block of a predetermined fixed length, wherein the bit length of the state value is less than the predetermined bit length of the produced block.