对多媒体加密的安晓，因此，加密算法应能抵御已知明文的攻击（known-plaintext attack）全性要求表现在两个方面：加密的视觉效果，即加密后的序列保留了多少视觉信息；传统的安全性能，即攻破安全系统的难易程度。2.2.
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提出了一种改进的安全信道建立算法，新的算法能够承受已知明文攻击，同时还提高了加、解密运算的效率。
A improved algorithm that builds security channel is provided, the new algorithm not only against known-plaintext attack, but also enhance efficiency of operation for encryption and decryption.
最后给出了对该类方案的已知明文的同态攻击方法，弥补了该类方案理论分析上的不足。
Homeostasis attack of this kind of scheme is also proposed with known plaintext, all of these could make up the shortcoming of theory analysis.
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