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User’s Manual for the Wireless Digital Media Player MP115
Wireless Networking Basics B-15
November 2004 202-10038-01
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 code (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
One of the encryption methods supported by WPA beside TKIP 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’s hardware in both the station and the access
point. TKIP was a pragmatic compromise that allows organizations to deploy better security while
AES capable equipment is being designed, manufactured, and incrementally deployed.