Question

简单替换密码是最常用的密码，包括为每个密文文本字符替换每个纯文本字符的算法。 在这个过程中，与凯撒密码算法相比，字母表是混乱的。

例子 (Example)

简单替换密码的密钥通常由26个字母组成。 一个示例关键是 -

plain alphabet : abcdefghijklmnopqrstuvwxyz
cipher alphabet: phqgiumeaylnofdxjkrcvstzwb

使用上述密钥的示例加密是 -

plaintext : defend the east wall of the castle
ciphertext: giuifg cei iprc tpnn du cei qprcni

以下代码显示了一个实现简单替换密码的程序 -

import random, sys
LETTERS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
def main():
   message = ''
   if len(sys.argv) > 1:
      with open(sys.argv[1], 'r') as f:
         message = f.read()
   else:
      message = raw_input("Enter your message: ")
   mode = raw_input("E for Encrypt, D for Decrypt: ")
   key = ''
   while checkKey(key) is False:
      key = raw_input("Enter 26 ALPHA key (leave blank for random key): ")
      if key == '':
         key = getRandomKey()
      if checkKey(key) is False:
		print('There is an error in the key or symbol set.')
   translated = translateMessage(message, key, mode)
   print('Using key: %s' % (key))
   if len(sys.argv) > 1:
      fileOut = 'enc.' + sys.argv[1]
      with open(fileOut, 'w') as f:
         f.write(translated)
      print('Success! File written to: %s' % (fileOut))
   else: print('Result: ' + translated)
# Store the key into list, sort it, convert back, compare to alphabet.
def checkKey(key):
   keyString = ''.join(sorted(list(key)))
   return keyString == LETTERS
def translateMessage(message, key, mode):
   translated = ''
   charsA = LETTERS
   charsB = key
   # If decrypt mode is detected, swap A and B
   if mode == 'D':
      charsA, charsB = charsB, charsA
   for symbol in message:
      if symbol.upper() in charsA:
         symIndex = charsA.find(symbol.upper())
         if symbol.isupper():
            translated += charsB[symIndex].upper()
         else:
            translated += charsB[symIndex].lower()
				else:
               translated += symbol
         return translated
def getRandomKey():
   randomList = list(LETTERS)
   random.shuffle(randomList)
   return ''.join(randomList)
if __name__ == '__main__':
   main()

输出 (Output)

实现上面给出的代码时，您可以观察到以下输出 -