Abstract: This paper points out that the substitute encryption algorithm proposed in reference1 cannot resist known-plaintext attack. The analyses show that the key of this cipher can be found with very few known plaintext-cipher pairs; and the permutation algorithm is only provided with very small key space. So an attack scheme is proposed, and the example of the attack scheme successfully brokes the encryption algorithm. A proposal for improvement algorithm is proposed, too.

Key words: Chaotic sequences, Sequence cipher, Image encryption, SP network

摘要： 指出文献[1]设计的加密算法中的替代变换算法不能抵抗已知明文攻击，由极少的明密文对就可求出密钥；且置换变换算法没有提供足够的密钥空间。据此提出了一种对该算法的攻击方案，并用实例对该加密算法进行攻击，证明攻击方案完全有效。同时，也提出了对该算法的改进建议。

关键词: 混沌序列, 序列密码, 图像加密, SP网络