Some Remarks on the TKIP Key Mixing Function of IEEE 802.11i

Temporal Key Integrity Protocol (TKIP) is a sub-protocol of IEEE 802.11i. TKIP remedies some security flaws in Wired Equivalent Privacy (WEP) Protocol. TKIP adds four new algorithms to WEP: a Message Integrity Code (MIC) called Michael, an Initialization Vector (IV) sequencing discipline, a key mixing function and a re-keying mechanism. The key mixing function, also called temporal key hash, de-correlates the IVs from weak keys. Some cryptographic properties of the S-box used in the key mixing function are investigated in this paper, such as regularity, avalanche effect, differ uniform and linear structure. V.Moen, H.Raddum and K.J.Hole pointed out that there existed a temporal key recovery attack in TKIP key mixing function. In this paper a method is proposed to defend against the attack, and the resulting effect on performance is also discussed.