STA-AP: WPA-PSK Connection Establishment (Sequence Diagram)

Summary

• Probe response and beacon frames include the WPA IE (AP WPA capabilities)
• Association request from STA includes the WPA IE (STA WPA capablities)
• IEs in EAPOL messages and corresponding probe/beacon/assoc messages should match
• WPA Pairwise Key (TKIP) is dervied from the following
• STA MAC address
• AP MAC address
• PMK (Pairwise Master Key) (PMK = PSK (256 bits))
• Authenticator (AP) Nonce (A random value genearted by AP)
• Supplicant (STA) Nonce (A random value generated by STA)
• Pairwise key consists of 
• EAPOL KEK (128 bits)
• EAPOL KCK (128 bits)
• TKIP TK (128 bits)
• TKIP MIC Key (128 bits)
• WPA does not use KEK to encrypt the keys (Q:What is the purpose of KEK in TKIP?)
• KCK is used for integrity protection of EAPOL messages
• Group key messages are encrypted using TKIP TK
• Group key consists of
• Group Temporal Key (128 bits)
• Group MIC (128 bits)
• Group key may be periodically updated by the AP
• Air-traces used to generate this diagram can be downloaded from here