As an expansion of LAN, the WLAN reduce the cost of building a network infrastructure, to enjoy the mobile, high-quality, multimedia services. The 802.11 standard for wireless networks includes a Wired Equivalent Privacy (WEP) protocol, which is used to protect link-layer communications from eavesdropping and other attacks. Several serious security flaws in this protocol have been discovered and some solutions have been proposed to enhance WEP security. However, it is doubtful whether they can provide enough security as these solutions lack precisely security analysis. In this paper, concrete security analyses of various enhancing mechanisms are given. Results show that these mechanisms indeed increase security and bring significant, provable security gains in WLAN environment. The authors quantify the security as a function of the security of the primitives used, thereby enabling a user to decide how to construct an enhanced mechanism for desired demands.