python实现维吉尼亚加密法-创新互联

本文实例为大家分享了python实现维吉尼亚加密法的具体代码，供大家参考，具体内容如下

Vigenere加密/解密时,把英文字母映射为0-25的数字再进行运算,并按n个字母为一组进行变换.算法定义如下:
设密钥 k =(k1,k2,k3…,kn),明文 m = (m1,m2,….mn)，则加密算法为:
Ek(m) = (c1,c2,…cn)
其中:c1 = (mi+ki)(mod 26),i=1,2,3…..n
解密算法为:
mi = (ci - ki)(mod 26), i = 1,2,…..n。

import string,os

def   vigenereEncrypt(msg,key):
    size = len(key)
    result = []
    cnt = 0
    for i in msg:
      if i.upper() in string.uppercase:
        #offset相当于是 ki
        offset = string.uppercase.find(key[cnt%size])
        t = string.uppercase[(string.uppercase.find(i.upper())+offset)%26] #这里相当于是c1 = (mi+ki)(mod 26) ,t = c1
        if i.isupper():
          result.append(t)
        else:
          result.append(t.lower())
        cnt+=1
      else:
        result.append(i)
    return "".join(result)
def   main():

    msg = "Common sense is not so common"
    cipher = vigenereEncrypt(msg,"PIZZA")#key = "PIZZA:

    print cipher
if   __name__=="__main__":
    main()