Abstract: Shannon put forward the concept of perfect secrecy and proved that some kinds of cryptosystems are perfect secrecy. The paper analyzes Shannon’s proof of some kinds of cryptosystems about perfect secrecy and points out that Bayes’ theorem was used mistakenly in proof because of mixing up the probabilities under different conditions. An example is given to show that one-time system isn’t perfect secrecy and this leads to a foundation for further study of cryptosystem’s secrecy. The paper educes the new direction of probability and discusses the problems of eclectic calculation probability under several conditions.

Key words: one-time system, cryptography, perfect secrecy, probability

摘要： 仙农提出了完善保密的概念并且证明了某些密码体制是完善保密的。就仙农对某些密码体制是完善保密的证明过程进行了分析，指出了其中对Bayes定理的误用，错误在于把不同的前提条件下的概率混淆带入了Bayes定理的等式中，举例证明这些密码体制不是完善保密的，为进一步完善密码体制的安全性提供了基础。引出了概率论的新方向，对多个条件下的概率折衷计算问题进行了相应的讨论。

关键词: 一次一密体制, 密码学, 完善保密, 概率

CLC Number: 

• TP309