Willi Meier

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Title: Near-colliding Keys in RC4

Abstract: Search of key collisions in the RC4 stream cipher has been an active area. We investigate near-colliding keys that lead to related states after key scheduling and related key stream bytes. Our investigation reveals that near-colliding states do not necessarily lead to near-colliding key streams. From this motivation, we present practical methods to find a related key pair with differences in two bytes, that leads to a large number of matches in the initial key stream. In the process, we discover a class of related key distinguishers for RC4. The best one of these shows that given a random key and a related one to that (the last two bytes increased and decreased by 1 respectively), the first pair of bytes corresponding to the related keys are the same with significant probability (e.g., approximately 0.011 for 16-byte keys to 0.044 for 30-byte keys).

Slides: Nearcollisionrc4.pdf