Security problems led to development of the 802.11i standard and a partial implementation of it, known as WPA. 802.11i introduces robust security protocols, including TKIP and CCMP, plus authentication and key management algorithms. TKIP works with existing WEP encryption hardware, whereas CCMP uses the AES algorithm for stronger security. TKIP uses a key mixing algorithm to protect the base Temporal Encryption Key and to help avoid RC4 weaknesses. It uses the Michael algorithm for message integrity but must protect Michael with additional countermeasures. CCMP uses two different modes of AES, one for confidentiality and the other for message integrity.
802.11i includes key management between APs and stations. Master keys are established by one of the EAP authentication methods. The master keys serve as the root of a key hierarchy. Transient keys are negotiated from the master keys using key handshakes. The 4-way handshake is used to prove liveness of the PMK and to establish a fresh PTK. The group key handshake is used to refresh the GTK. 802.11i has taken years to be developed. WPA is a subset of 802.11i that was adopted by the Wi-Fi Alliance to get some of the benefits of 802.11i to market quickly. Cisco also implemented a protocol suite called CKIP for the same purpose. 802.11i will supplant CKIP and WPA.
802.11i addresses the known attacks with WEP in addition to some of the other attacks on 802.11 in general. It does not deal with weaknesses in EAP methods such as LEAP and PEAP.