摘要
无线局域网提供了传统有线网络所不具备的移动性和灵活性,因而得到了广泛的应用,但是同时也带来了很多安全问题。目前,这些安全问题逐渐引起了人们的关注。当用户采用射频信号作为介质进行数据传输时,遭受侦听和仿冒的威胁无处不在,因此需要提供一种安全机制来保护正常的通信。
IEEE 802.11标准引入了有线等价保密(WEP)协议来保护链路层的通信,其目标是为无线局域网数据提供与有线网络相同级别的安全保护。WEP的主要任务就是保护用户数据的机密性,使其免受诸如窃听之类的攻击。
通过分析WEP协议,发现该协议中存在一些严重的安全缺陷(如密钥流重用、消息认证、消息解密等),从而说明WEP并未能达到设计时的安全目标。然后,提出了利用这些缺陷向无线局域网发起攻击的方法。
基于这些攻击方法,设计了针对802.11无线局域网的攻击工具。该工具通过将无线网卡设置为监听模式,来实现数据包的捕获。然后,对捕获的数据包进行分析和过滤,获取相关的网络信息(如AP的MAC地址、SSID、频道等)。最后,对加密的数据进行计算,获得用户使用的加密密钥。
在Windows XP操作系统下,基于Microsoft Visual C++ 6.0平台实现了该无线局域网攻击工具的原型。理论分析和实验测试表明,该工具能够发现正在进行数据传输的基本服务集,并对其使用的加密密钥进行破解。
Wireless LAN has the mobility and flexibility, which cannot be provided by the traditional wired network. As a result, wireless LAN has gained much popularity. But with the added convenience of wireless access come new problems, not the least of which are heightened security concerns. When transmissions are broadcast over radio waves, interception and masquerading become trivial to anyone with a radio, and so there is a need to employ security mechanisms to protect the communications.
The 802.11 standard for wireless LAN communications introduces the Wired Equivalent Privacy protocol, used to protect link-layer communications, in an attempt to bring the security level of wireless systems closer to that of wired ones. The primary goal of WEP is to protect the confidentiality of user data from eavesdropping and other attacks.
Through analysis of WEP, several serious security flaws are discovered in the protocol, which shows that WEP fails to attain its security goals. Exploiting these flaws,some approaches are proposed to launch attacks against wireless LANs.
Based on these attack approaches, an attack tool is designed against 802.11 WLAN. By setting wireless card as RF monitoring mode, this tool can capture packets in WLAN. Then, this tool analyzes and filters the packets captured to acquire relevant information about the network, such as MAC address of AP, SSID and channel. Finally, by computing the data encrypted, the user’s encryption key is obtained.
The prototype of the WLAN attack tool is implemented under Windows XP with Microsoft Visual C++ 6.0. Theoretical analysis and experiment show that the tool can discover the basic service set being transmitted, and crack the key used to encrypt data in the BSS.
引文
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