te with the attacker. Rogue access point (or evil twin intercept) - an attacker installs an unauthorised access point with the correct SSID (the twin). If the signal is strengthened using an amplifier or high gain antenna, clients stations will preferentially associate with the rogue access point and sensitive data will be compromised. Cryptoanalytic attacks - an attack in which the attacker uses a theoretical weakness to break the cryptographic system. An example is the weakness of the RC4 cipher that leads to the Chapter Eight vulnerability in WEP (see the Section "WEP Wired Equivalent, Privacy Encryption, p. 209"). Side channel attacks - an attack in which the attacker uses physical information, such as power consumption, timing information or acoustic or electromagnetic emissions to gain information about the cryptographic system. Analysis of this information might allow the attacker to determine an encryption key directly or a plaintext message from which the key can be computed. Although the range of threats is wide and varied, in most cases executing these kinds of attack requires a high level of technical expertise on the part of the hacker. The risk to network security can be significantly reduced by enabling the full range of available security measures described in the following sections. WLAN Security Table 8-1 summarises the range of generic security measures that have been developed to protect wireless LANs from the threats and vulnerabilities described above. As described in the Section "WEP - Wired Equivalent Privacy Encryption, p. 209", the original 802.11 standard included only limited Table 8-1: Wireless LAN Security Measures Security measure Description User authentication Confirms that users who attempt to gain access to the network are who they say they are. User access control Allows access to the network only to those authenticated users who are permitted access. Data privacy Ensures that data transmitted over the network is protected by encryption from eavesdropping or any other unauthori