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4.1基于线性变换一矩阵的双字母代替体制在前一章我们已经看到:采用单个字母以及它们的组合的频率的各种各样的技术能使密码分析人员有可能对付不同类型的代替密表。我们可以想象得到,只要加密单元仍然是单个字母,即便是更复杂的加密方法,上述结论也是正确的。使用密码的人为了防止用字母频率分析来得到密码分析成果,可以用一群字母而不是一个字母作为加密单元。我们把一群n个明文字母作为一个单元用n个密文字母来代替的密码体制称为多字母代替体制。
4.1 Two-letter Substitutions Based on a Linear Transform-Matrix In the previous chapter we have seen that the various techniques that employ the frequencies of single letters and their combinations can make it possible for the cryptanalyst to deal with different types of proxies . We can imagine that as long as the encryption unit is still a single letter, even the more complex encryption method, the above conclusion is correct. In order to prevent the use of password frequency analysis to get the results of cryptanalysis, you can use a group of letters instead of a letter as an encryption unit. We refer to a group of n plaintext letters as a unit with n ciphertext letters instead of the password system as a multi-letter replacement system.