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Wireless Data Technologies reference phần 7

Wired Equivalent Privacy (WEP) được thiết kế bởi IEEE đưa WLAN bảo mật đến một mức độ so sánh với một môi trường mạng có dây như một mạng nội bộ (LAN). WEP sử dụng một tính năng bảo mật được sử dụng rộng rãi trong ngành công nghiệp bảo mật được gọi là mã hóa. | 134 WIRELESS DATA NETWORKS 11 9 17 15 1 25 23 21 19 7 5 3 1 24 22 20 18 16 14 12 10 8 6 4 2 5 0 c 0 c o SNR 10-15 dB datarate 5.5 Mb SNR 15 dB datarate 11 Mb Figure 8.20 Side area placement signal-to-noise ratio APs. Theoretically the client s wireless Network Interface Card NIC should be configured with the same SSID as the AP in order to join the network. 8.10.2 WEP - Wired Equivalent Privacy Wired Equivalent Privacy WEP was designed by the IEEE to bring WLAN security to a level comparable to a wired networking environment such as a Local Area Network LAN . WEP uses a security feature widely used throughout the security industry known as encryption. OVERVIEW OF 802.11B SECURITY MECHANISMS 135 WEP s encryption process uses a symmetric key and a mathematical algorithm to convert data into an unreadable format called cipher-text. In cryptography a symmetric key is a variable length value used to encrypt or decrypt a block of data. Any device needing to participate in the symmetric encryption process must possess the same key. WEP keys are configured by the WLAN administrator and the larger the key the harder it will be to break the encryption cipher. RC4 is the encryption algorithm used by WEP and it needs the assistance of an Initialization Vector IV . An IV is a pseudo-random binary string used to jump-start the encryption process for algorithms that depend on a previous sequence of cipher-text blocks. A smaller IV in conjunction with keys that do not frequently change will increase the chances that encrypted data packets will duplicate the IV. WEP consists of up to four variable length symmetric keys based on the RC4 stream cipher. All keys are static in nature and are common to all devices on the WLAN. This means that the WEP keys are manually configured on the WLAN devices and will not change until the administrator configures different keys. Most 802.11b equipment comes with two key sizes. The two key sizes are shown below. 64-bit 40-bit Key and a 24-bit .