TCP/IP Tutorial and Technical Overview - IBM Redbooks

Security
The airborne nature of WiFi inherently makes it susceptible to security risks. No
longer hindered by the need to gain access to a wire, malicious users attempting
to capture data transfers must only gain proximity to the intended victim. As
such, several encryption protocols have been coupled with WiFi in order to
secure the data transferred using WiFi.
Wireless Equivalent Privacy (WEP)
Initially, WEP was used to secure WiFi communications. It uses RC4, or
ARCFOUR, stream cipher to provide confidentiality. Additionally, WEP employs
a 33-bit cyclic redundancy check (CRC-32) to ensure data integrity. However,
WEP uses a shared encryption key to which all users must have access in order
to authenticate with the WAP. This compromises the security of the network
because current hacking technology can decode the key using freely distributed
programs. Additionally, WEP security, because it employs a stream cipher, is
susceptible to stream cipher attacks. Due to these and other shortcomings, WEP
has been outdated by WiFi Protected Access (WPA and WPA2).
WiFi Protected Access (WPA)
Created by the Wi-Fi Alliance, WPA also employs a pass phrase concept similar
to that of the WEP implementation. However, WPA uses distributed private keys
administered by an 802.1X authentication server.
Note: A public-shared key (PSK) mode can be used, but it is less secure.
Data encryption is again provided through the RC4 stream cipher, which uses a
128-bit key and a 48-bit initialization vector. Security is increased by inserting
dynamic key changes using the Temporal Key Integrity Protocol (TKIP). Data
integrity is guaranteed using the Message Integrity Code (MIC) algorithm, also
called Michael’s algorithm.
While this increased security implementation compensates for the faults found
previously with WEP, cryptoanalysts have still found weaknesses in the WPA
architecture. Specifically, Michael’s algorithm was chosen because it still allowed
mobile devices using WPA to communicate with access points still using WEP,
and vice versa. However, the algorithm is still susceptible to packet forgery
attacks. To combat this, WPA was enhanced and expanded into WPA2.
WiFi Protected Access (WPA2)
In WPA2, Michael’s algorithm is replaced by the Counter Mode with Cipher Block
Chaining Message Authentication Protocol (CCMP). Because CCMP provides
both data integrity and key management using the Advanced Encryption
Standard (AES, also known as Rijndael), it combines both the data integrity and
Chapter 10. Wireless IP 399