code: def decode(self, decrypted):
          
          pad = ord(decrypted[-1])
          if pad < 1 or pad > 32:
              pad = 0
          return decrypted[:-pad]
docs: 删除解密后明文的补位字符
          @param decrypted: 解密后的明文
          @return: 删除补位字符后的明文