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ZyXEL G-270S User’s Guide
Appendix D Types of EAP Authentication 77
WPA(2)
User Authentication
WPA or WPA2 applies IEEE 802.1x and Extensible Authentication Protocol (EAP) to
authenticate wireless stations using an external RADIUS database.
Encryption
Both WPA and WPA2 improve data encryption by using Temporal Key Integrity Protocol
(TKIP), Message Integrity Check (MIC) and IEEE 802.1x. In addition to TKIP, WPA2 also
uses Advanced Encryption Standard (AES) in the Counter mode with Cipher block chaining
Message authentication code Protocol (CCMP) to offer stronger encryption.
TKIP uses 128-bit keys that are dynamically generated and distributed by the authentication
server. It includes 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 regularly changes and rotates 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 stations. This all happens in the background automatically.
WPA2 AES (Advanced Encryption Standard) is a block cipher that uses a 256-bit
mathematical algorithm called Rijndael.
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), TKIP makes it much more difficult to decrypt data on a Wi-Fi
network than WEP, making it 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
an easier-to-use, consistent, single, alphanumeric password.