ZyXEL Communications P-660HW-T - V2, Руководство пользователя

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P-660HW-T v2 User’s Guide
330 Appendix K Wireless LANs
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
Both WPA and WPA2 improve data encryption by using Temporal Key Integrity Protocol
(TKIP), Message Integrity Check (MIC) and IEEE 802.1x. WPA and WPA2 use Advanced
Encryption Standard (AES) in the Counter mode with Cipher block chaining Message
authentication code Protocol (CCMP) to offer stronger encryption than TKIP.
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.
The Message Integrity Check (MIC) is designed to prevent an attacker from capturing data
packets, altering them and resending them. The MIC provides a strong mathematical function
in which the receiver and the transmitter each compute and then compare the MIC. If they do
not match, it is assumed that the data has been tampered with and the packet is dropped.
By generating unique data encryption keys for every data packet and by creating an integrity
checking mechanism (MIC), with TKIP and AES it is more difficult to decrypt data on a Wi-Fi
network than WEP and difficult for an intruder to break into the network.
The encryption mechanisms used for WPA(2) and WPA(2)-PSK are the same. The only
difference between the two is that WPA(2)-PSK uses a simple common password, instead of
user-specific credentials. The common-password approach makes WPA(2)-PSK susceptible to
brute-force password-guessing attacks but it’s still an improvement over WEP as it employs a
consistent, single, alphanumeric password to derive a PMK which is used to generate unique
temporal encryption keys. This prevent all wireless devices sharing the same encryption keys.
(a weakness of WEP)