NETGEAR ProSafe WG302 Reference Manual page 98

Reference Manual for the NETGEAR ProSafe 802.11g Wireless Access Point WG302
If configured to implement dynamic key exchange, the 802.1x authentication server can return
session keys to the access point along with the accept message. The access point uses the session
keys to build, sign and encrypt an EAP key message that is sent to the client immediately after
sending the success message. The client can then use contents of the key message to define
applicable encryption keys. In typical 802.1x implementations, the client can automatically change
encryption keys as often as necessary to minimize the possibility of eavesdroppers having enough
time to crack the key in current use.
Temporal Key Integrity Protocol (TKIP). WPA uses TKIP to provide important data
encryption enhancements including a per-packet key mixing function, a message integrity check
(MIC) named Michael, an extended initialization vector (IV) with sequencing rules, and a
re-keying mechanism. TKIP also provides for the following:
• The verification of the security configuration after the encryption keys are determined.
• The synchronized changing of the unicast encryption key for each frame.
• The determination of a unique starting unicast encryption key for each preshared key
authentication.
Michael. With 802.11 and WEP, data integrity is provided by a 32-bit integrity check value (ICV)
that is appended to the 802.11 payload and encrypted with WEP. Although the ICV is encrypted,
you can use cryptanalysis to change bits in the encrypted payload and update the encrypted ICV
without being detected by the receiver.
With WPA, a method known as Michael specifies a new algorithm that calculates an 8-byte
message integrity check (MIC) using the calculation facilities available on existing wireless
devices. The MIC is placed between the data portion of the IEEE 802.11 frame and the 4-byte ICV.
The MIC field is encrypted together with the frame data and the ICV.
Michael also provides replay protection. A new frame counter in the IEEE 802.11 frame is used to
prevent replay attacks.
AES Support for WPA2. One of the encryption methods supported by WPA2 is the advanced
encryption standard (AES), although AES support will not be required initially for Wi-Fi
certification. This is viewed as the optimal choice for security conscience organizations, but the
problem with AES is that it requires a fundamental redesign of the NIC hardware in both the
station and the access point. TKIP is a pragmatic compromise that allows organizations to deploy
better security while AES capable equipment is being designed, manufactured, and incrementally
deployed.
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v0.1, December 2005
Wireless Networking Basics