On the anaysis of stream cipher and its implementation

流密码是一种广泛使用的安全协议。特别是，RC4作为一种标准的加密算法被WEP、WPA、SSL/TLS等许多标准协议所采用。我们基于流密码对这些协议进行了评估。首先，我们独立地在广播环境下提出了实用的针对SSL/TLS中RC4的明文恢复攻击。我们给出了一种主动攻击，即将目标明文字节的位置滑动到明文后面的字节。我们的攻击通过使用恶意的JavaScript将任何字节注入明文的头部。它提高了恢复大量明文字节的概率。其次，针对密钥恢复攻击，提出了一种安全的WEP操作。该方法需要攻击者至少100,000个数据包才能恢复WEP密钥。最后，我们提出了一种在真实环境下的可执行攻击，而不需要对WPA-TKIP进行中间人攻击。

Stream cipher is a widely-used in secured protocols. Especially, RC4 is adopted in a lot of standard protocols such as WEP, WPA and SSL/TLS as a standard encryption algorithm. We present the evaluation of these protocols based on the stream cipher. Firstly, we proposed practical plaintext recovery attacks on RC4 in SSL/TLS in the broadcast setting, independently. We give an active attack, which is a method to slide the position of a target plaintext byte into later byte of the plaintext. Our attack injects any bytes into the head of the plaintext by using malicious JavaScript. It causes improvement in probability for recovering a lot of plaintext bytes. Secondly, we propose a secure WEP operation against key recovery attacks. The proposed method requires for attackers at least 100,000 packets to recover the WEP key. At last, we propose an executable attack in a real environment without requiring the man-in-the-middle attack on WPA-TKIP.