RC4 is probably the simplest and the most widely-used software stream cipher in the world today. It has only a few lines of code, but it is also quite secure -- to a large extent, despite some weaknesses in its key schedule -- due to the highly non-linear structure of the swap function in the algorithm. In this work we analyze the key scheduling algorithm of RC4, and investigate the relations between bytes of the encryption key and the entries of the state table. We give a method to derive the state table partially from a partially known encryption key. We also analyze a class of related keys which yield similar state tables and produce key streams that are similar at the initial bytes.

DATE: 5 March, 2007, Monday@ 16:40
PLACE: EA 409