ZyXEL Communications ZYWALL USG 20 Manual page 815

The RADIUS server distributes the PMK to the AP. The AP then sets up a key
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hierarchy and management system, using the PMK to dynamically generate
unique data encryption keys. The keys are used to encrypt every data packet that
is wirelessly communicated between the AP and the wireless clients.
Figure 453 WPA(2) with RADIUS Application Example
WPA(2)-PSK Application Example
A WPA(2)-PSK application looks as follows.
First enter identical passwords into the AP and all wireless clients. The Pre-Shared
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Key (PSK) must consist of between 8 and 63 ASCII characters or 64 hexadecimal
characters (including spaces and symbols).
The AP checks each wireless client's password and allows it to join the network
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only if the password matches.
The AP and wireless clients generate a common PMK (Pairwise Master Key). The
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key itself is not sent over the network, but is derived from the PSK and the SSID.
ZyWALL USG 20/20W User's Guide
Appendix C Wireless LANs
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