tailieunhanh - wifi security phần 6

Với tất cả các cuộc tấn công kích hoạt nó không phải là phổ biến để phục hồi các khóa WEP sau khi thu thập ít hơn 300,000 IVs độc đáo. Các công cụ Aircrack được sử dụng để chứng minh các cuộc tấn công trong luận án này. Khi sử dụng Aircrack, các bước trên được phân chia giữa hai công cụ. Airodump chụp các khung hình và các bản ghi | . WIRED EQUIVALENT PRIVACY WEP 39 point replies to the client with a positive authentication response if not a negative response. Shared key authentication can operate in both WEP encrypted networks and non-encrypted networks. In the latter case WEP and a secret WEP key is still a requirement except all traffic is sent in cleartext. The idea is that some might not wish to have the overhead of WEP encryption yet only authorized clients should have access to the network. One-Way Authentication A widely known weakness of the protocol is that there really only is a one-way authentication taking place. The client authenticates itself to the access point but the access point does not authenticate itself to the client. Thus it is possible to setup a fake access point which masquerades as the real access point and accepts the real access point s clients. The fake access points are known as rogue access points. If the meaning of the first frame was changed from authenticate me to authenticate yourself then full authentication would be possible. The client could ask the access point to authenticate then the access point could ask the client to do the same. Anyone Can Get Authenticated There is a much bigger weakness than the one-way authentication issue. Anyone who has a key sequence and IV of at least 136 bytes can authenticate to the access From Figure Equations and show how a real client constructs the response to the challenge Keysequence RC4 IV II WEPkey ICV CRC32 nonce E nonce nonce II ICV Keysequence Notice that the step shown in Equation is possible to skip if a key sequence and IV is already known. The requirement to know the WEP key is eliminated. Depending on the implementation in the access point one may capture a valid challenge-response session to obtain the key sequence. A good implementation should not allow the same IV to be used more than once ever. However the standard only implies that it .

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