ZyXEL Communications VSG1435-B101 - V1.10, Руководство пользователя

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Appendix D Wireless LANs
VSG1435-B101 Series User’s Guide
378
WPA and WPA2
Wi-Fi Protected Access (WPA) is a subset of the IEEE 802.11i standard. WPA2
(IEEE 802.11i) is a wireless security standard that defines stronger encryption,
authentication and key management than WPA.
Key differences between WPA or WPA2 and WEP are improved data encryption and
user authentication.
If both an AP and the wireless clients support WPA2 and you have an external
RADIUS server, use WPA2 for stronger data encryption. If you don't have an
external RADIUS server, you should use WPA2-PSK (WPA2-Pre-Shared Key) that
only requires a single (identical) password entered into each access point, wireless
gateway and wireless client. As long as the passwords match, a wireless client will
be granted access to a WLAN.
If the AP or the wireless clients do not support WPA2, just use WPA or WPA-PSK
depending on whether you have an external RADIUS server or not.
Select WEP only when the AP and/or wireless clients do not support WPA or WPA2.
WEP is less secure than WPA or WPA2.
Encryption
WPA improves data encryption by using Temporal Key Integrity Protocol (TKIP),
Message Integrity Check (MIC) and IEEE 802.1x. WPA2 also uses TKIP when
required for compatibility reasons, but offers stronger encryption than TKIP with
Advanced Encryption Standard (AES) in the Counter mode with Cipher block
chaining Message authentication code Protocol (CCMP).
TKIP uses 128-bit keys that are dynamically generated and distributed by the
authentication server. AES (Advanced Encryption Standard) is a block cipher that
uses a 256-bit mathematical algorithm called Rijndael. They both include 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.
WPA and WPA2 regularly change and rotate the encryption keys so that the same
encryption key is never used twice.
The RADIUS server distributes a Pairwise Master Key (PMK) key to the AP that
then sets up a key hierarchy and management system, using the PMK to
dynamically generate unique data encryption keys to encrypt every data packet
that is wirelessly communicated between the AP and the wireless clients. This all
happens in the background automatically.