Cryptanalysis of KSAm-like Algorithms

Abstract

RC4 is one of the most widely used stream cipher. It is fairly simple and efficient, and is used, among other things, in WEP, TKIP and SSL/TLS protocols. Fluhrer, Mantin and Shamir show that RC4 is completely insecure in the WEP mode of operation, and most of the discovered weaknesses are related to the key-scheduling algorithm (KSA) part of RC4. Crainicu and Boian propose a new variant of key-scheduling algoritm, called KSAm, whose primary goal is to address the Fluhrer-Mantin-Shamir (FMS) weakness of WEP-like cryptosystems, where IV (initialization vector) precedes the secret key. Cryptanalysis of KSAm reveals that the FMS IV weakness is removed by destroying the FMS resolved condition. This paper summarizes the previous security analyses of KSAm, examines KSAm in the WEP mode of operation, where IV follows the secret key, and discusses new security aspects like the effect of other FMS weak keys and Roos weak keys on KSAm and the randomness of the state tablepsila first entries after KSAm completion.