密码学是研究编制密码和破译密码的技术科学。其包括多种密码编译破译方法,替换式密码就是其中之一。本文针对替换式密码设计出长短密文下的两种数学模型来破译密文,并设计出一个衡量破译能力的标准,来评价破译的能力。本文充分利用MATLAB、excel等多种语言的特性,进行综合编程及数据统计,对数据进行了分析处理,并设计简单易懂的算法使破译准确性更高。 Cryptography is a technical science that studies the compilation of passwords and deciphering of passwords. It includes a variety of password compilation and decryption methods, replacement password is one of them. This paper designs two kinds of mathematical models under short and long ciphertexts for the replacement password to decipher the ciphertext and designs a standard to measure the deciphering ability to evaluate the deciphering ability. This article makes full use of many languages ​​such as MATLAB, excel and so on, carries on the comprehensive programming and the data statistics, carries on the analysis processing to the data, and designs the easy-to-understand algorithm to make decipher the accuracy higher.