Abstract: RC4 stream cipher algorithm is vulnerable to weakness-key attack, distinguishing attack. Against the above attacks, this paper proposes an improved RC4 algorithm based on random permutation, which uses the dynamic status table to make nonlinear transformation operation and extends value of the elements in the state table. The output of keystream will be made by both the previous state and the next state of table. The validity, security and performance anti-attacking of the improved algorithms are analyzed. Experiment results show that the keystream randomness of improved algorithm and efficiency are superior to RC4 algorithm.

Key words: RC4, stream cipher, state table, randomness of keystream

摘要： RC4流密码算法易受弱密钥攻击、区分攻击和错误引入攻击。针对上述攻击，提出了一种基于随机置换的改进算法，该算法采用动态的状态表进行非线性运算，扩展状态表中的元素的取值空间，密钥序列的输出由状态表的前一状态和后一状态共同决定，提高了算法的安全性。分析了改进算法的正确性、安全性以及抗攻击性。实验验证了改进算法的密钥流随机性和效率优于RC4算法。

关键词: RC4, 流密码, 状态表, 密钥流随机性