Analysis of the 802.11i 4-Way Handshake

Overview

802.11i is an IEEE standard designed to provide enhanced MAC security in wireless networks. The authentication process involves three entities: the supplicant, the authenticator, and the authentication server. A 4-Way Handshake must be executed between the supplicant and the authenticator to derive a fresh pairwise key and/or group key for subsequent data transmissions. The paper analyzes the 4-Way Handshake protocol using a finite-state verification tool and finds a Denial-of-Service attack. The attack involves forging initial messages from the authenticator to the supplicant to produce inconsistent keys in peers. Three repairs are proposed; based on various considerations, the third one appears to be the best.