Cryptology ePrint Archive: Report 2013/748

Plaintext Recovery Attacks Against WPA/TKIP

Kenneth G. Paterson and Bertram Poettering and Jacob C.N. Schuldt

Abstract: We conduct an analysis of the RC4 algorithm as it is used in the IEEE WPA/TKIP wireless standard. In that standard, RC4 keys are computed on a per-frame basis, with specific key bytes being set to known values that depend on 2 bytes of the WPA frame counter (called the TSC). We observe very large, TSC-dependent biases in the RC4 keystream when the algorithm is keyed according to the WPA specification. These biases permit us to mount an effective statistical, plaintext-recovering attack in the situation where the same plaintext is encrypted in many different frames (the so-called ``broadcast attack'' setting). We assess the practical impact of these attacks on WPA/TKIP.

Category / Keywords: secret-key cryptography /

Date: received 13 Nov 2013, last revised 1 Mar 2014

Contact author: kenny paterson at rhul ac uk

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Version: 20140301:092833 (All versions of this report)

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