Question

为什么这个转置解密代码无法使用某些密钥？

def transencrypt(word,key):
    '''Traspositon encryption function. This function is used to encrypt a line
using the transposition encryption method. To know how transpositon encryption
works you can visit here https://en.wikipedia.org/wiki/Transposition_cipher.'''
    count1=0
    count2=0
    encrypted=''
    encryptbox=['']*key
    while count1<key:
        count2=count1
        while count2<len(word):
            encryptbox[count1]+=word[count2]
            count2+=key
        encrypted+=encryptbox[count1]
        count1+=1
    return encrypted

def transdecrypt(word,key):
    '''This Function is for the decrypting the encrypted strings encrypted by
transencrypt().This function only requires the encrypted string and the key
with which it has been decrypted.'''
    import math
    count1=0
    count2=0
    decrypted=''
    col=int(math.ceil(len(word)/key))
    decryptbox=['']*col
    while count1<col:
        count2=count1
        while count2<len(word):
            decryptbox[count1]+=word[count2]
            count2+=col
        decrypted+=decryptbox[count1]
        count1+=1
    return decrypted

print(transencrypt('hello world',5))
print(transdecrypt('h dewlolrol',5))

OP's original code source

我尝试使用密钥5加密“hello world”，但在解密时我得到了错误的结果。使用其他键可以正常工作。

Answer 1

问题是字符串长度（11）没有均匀分配到密钥（5）中，因此字符串"hello world"会编码到组h d-ew-lo-lr-ol中，即"h dewlolrol" 。哪个没问题，但解密例程将"h dewlolrol"切换为h d-ewl-olr-ol并生成错误的结果"heoo wlldlr"。

解决此问题的几种可能方法：

1）将encryptbox字符串替换为数组，并将加密单位填充为均匀宽度的段：h d-ew -lo -lr -ol，即"h dew lo lr ol "

这将允许您的解密例程工作，但您将在解密结束时以空格结束，并且加密的字符串将与原始字符串的大小不同。

或

2）动态调整解密逻辑，根据要解码的剩余字符串的长度以及剩余的预期段数，段必须缩小的数量来确定。这意味着您的解密例程与现在的加密例程类似。但它允许您处理当前加密例程的输出，加密字符串可以保持与原始字符串相同的长度。

下面是上面方法＃2的粗略返工 - 您可以看到它允许加密例程保持简单，但解密例程必须更复杂才能弥补它：

import math def transencrypt(string, key): ''' Transpositon encryption function. This function is used to encrypt a line using the transposition encryption method. To learn how transpositon encryption works you can visit here https://en.wikipedia.org/wiki/Transposition_cipher. ''' encrypted = '' length = len(string) for start in range(key): for offset in range(start, length, key): encrypted += string[offset] return encrypted def transdecrypt(string, key): ''' This function is for the decrypting the strings encrypted by transencrypt(). This function only requires the encrypted string and the key with which it was decrypted. ''' decrypted = '' length = len(string) width = int(math.ceil(length / key)) for start in range(width): offset = start remaining_key = key remaining_length = length remaining_width = width while offset < length: decrypted += string[offset] offset += remaining_width remaining_key -= 1 if remaining_key > 0: remaining_length -= remaining_width remaining_width = int(math.ceil(remaining_length / remaining_key)) return decrypted[:length] if __name__ == '__main__': import sys string = sys.argv[1] key = int(sys.argv[2]) print(transencrypt(string, key)) print(transdecrypt(transencrypt(string, key), key))

** OUTPUT *

> python3 test.py "hello world" 5 h dewlolrol hello world >

转置解密不适用于某些键？

1 个答案: