ASCII Vigenere密码未正确解密 [英] ASCII Vigenere cipher not decrypting properly

问题描述

我的Vigenere密码程序全部归结为两个列表。一个ASCII码列表，表示要加密/解密的消息的字符，另一个是将用于解密/加密消息的密钥的ASCII号码列表。

对于加密：

  encryption = [（（x + y）％26）+ ord '）如果x < 128 else x for x，y in zip（msglist，keylist）] 
  

解密：

  encryption = [（（x  -  y）％26）+ ord（'A'）如果x < 128 else x for x，y in zip（msglist，keylist）] 
  

如果我输入Python加密密钥爱我得到：

  GYAXLN 
  

不幸的是，当我尝试使用相同的密钥解密GYAXLN时，我得到：

  PEZNUT 
  

哪些不是应该的。我认为我的数学有问题，但是我不能很好地得到它，直到现在已经尝试了不同的数字，看看什么有用（我不是最好的数学）。我在这里缺少什么？

解决方案

问题在语句（x - y）％26 因为一个数字的mod定义为0到m-1，在上述情况下为0到25，但是减去你会得到负数，所以为了得到正确的结果你应该这样做（x - y + 26）％26 。如果我们在（xy）中得到的负值低于-m，低于-26，那么否仍然是否定的，那么你必须使它是正面的，这里是伪代码：

  val =（x  -  y）％26 
 while （val <0）val + = 26 
 val = val％26 
  

My Vigenere cipher program has all come down to two lists. One a list of ASCII numbers which represent the characters of the message to be encrypted/decrypted and the other is a list of ASCII numbers of the key that would be used to decrypt/encrypt the message.

For encryption:

encryption = [((x + y) % 26) + ord('A') if x < 128 else x for x, y in zip(msglist, keylist)]

for decryption:

encryption = [((x - y) % 26) + ord('A') if x < 128 else x for x, y in zip(msglist, keylist)]

If I input 'Python' with the key 'love' to encrypt I get:

GYAXLN

Unfortunately, when I try to decrypt 'GYAXLN' using the same key I get:

PEZNUT

Which is not what it should be. I think there is something wrong with my math but I just can't quite get it right and up till now have been trying different numbers to see what works (I'm not the best at maths). What am I missing here? Can it not all be done in a list comprehension?

解决方案

The problem is in the statement (x - y) % 26 because mod of a number is defined from 0 to m-1, in the above case 0 to 25, but while subtracting you get negative numbers, so in order to get the correct result you should do this (x - y + 26) % 26. If the negative value we get by (x-y) is lower than "-m" in the above case lower than -26, then the no still remains negative, then you have to make it positive, here is the pseudo code for that :

val = (x - y) % 26
while(val < 0) val += 26
val = val % 26

这篇关于ASCII Vigenere密码未正确解密的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！