802.1x, Encryption and Authentication - WPA, 802.11i and WPA2

WPA is a standards based solution to address vulnerabilities in WEP.

Main features:

Authenticated Key Management - authentication via IEEE 802.1x or PSK
Unicast or broadcast key management - after successful user authentication message integrity and encryption keys are derived, distributed validated and stored on the client and AP
Utilisation of TKIP and MIC - Temporal Key Integrity Protocol (TKIP) and Message Integrity Check (MIC) are elements of the WPA standard.
Initialisation Vector Space Expansion - Per-packet keying via IV hashing and key rotation. IV is expanded from WE 24bits to 48bits.

WPA/802.11i authentication process:
Client and AP exchange initial associated request (probe) and agree security capability. Client authenticated by 802.1x Radius server. When successfully authenticated the server and client will present the same master key (PKM) to the AP. Next a four-way key handshake between client and server takes place, finally a two-way handshake between client and AP takes place a group transient key (GTK) which includes MIC.

Issues of WPA:
- Reliant on RC4
- Hardware may not support WPA
- WPA susceptible to DOS, if two bad MICs occur the BSSID is shutdown for 1 minute
- Dictionary attacks can reveal PSK