Weaknesses in the Key Scheduling Algorithm of RC4

Abstract. Inthis paper we present several weaknesses in the keyscheduling algorithm of RC4, and describe their cryptanalytic signi cance. We identify a large number of weak keys, in which knowledge of a small number of key bits su ces to determine many state and output bits with non-negligible probability. We use these weak keys to construct new distinguishers for RC4, and to mount related key attacks with practical complexities. Finally, we show that RC4 is completely insecure in a common mode of operation which is used in the widely deployed Wired Equivalent Privacy protocol WEP, which is part of the 802.11 standard, in which a xed secret key is concatenated with known IV modi ers in order to encrypt di erent messages. Our new passive ciphertext-only attack on this mode can recover an arbitrarily long key in a negligible amount of time which grows only linearly with its size, both for 24 and 128 bit IV modi ers.

• Type: Conference
• Year: 2001
• Where: SACRYPT
• Authors: Scott R. Fluhrer, Itsik Mantin, Adi Shamir
• Keywords: Bits Su Ces, Cryptology, IV Modi Ers, SACRYPT 2001, Weak Keys