Lancom Systems LCOS 3.50

LANCOM Reference Manual LCOS 3.50  Chapter 11: Wireless LAN – WLAN

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Wireless LAN – WLAN

A simplified procedure for deriving the Master Secret mentioned in the

last section, which can be performed without a RADIUS server.

Negotiation of encryption procedure between access point and client.

TKIP

TKIP stands for Temporal Key Integrity Protocol. As the name suggests, it

involves an intermediate solution for temporary use until a truly strong

encryption procedure is introduced, but which deals with the problems of

WEP, never the less. One design requirement was therefore that the new

encryption procedure should be implementable on existing WEP/RC4

hardware with a reasonab le effort. When TKIP was defined, it was already

foreseeable that it would be used well into the era of 54/108Mbit LANs, and

a purely software-based encryption would be associated with too high a

speed penalty on most systems. In the 'block diagram' of TKIP (Figure 3),

therefore, there are many components of WEP to be seen, which generally

exist in hardware in WEP c ards and thus can effective ly be used for TKIP.

As components already familiar from WEP, one recognises the RC4 engine

used for the actual encryption and decryption, as well as the CRC module. As

Figure 3: Procedure for TKIP/Michael

Data

Data + Michael + CRC

CRC

Key mixing

(phase 1)

IVHi

Generator XOR

RC4

Michael key

Michael

Data + Michael

Source MAC address

TKIP key

Key mixing

(phase 2)

IVLo

Data + Michael + CRC (encrypted)

IVHi IVLo

TKIP

Michael