0x00 前言

CTF 加解密合集：CTF 加解密合集

0x01 题目

自动钥匙⊕

明文全大写，得到后转小写，并以_连接单词。

fsskryenvkm~jl{ejs}jwflzsnpgmifq{{j{|suhzrjppnx|qvixt~whu

0x02 Write Up

首先提示需要异或，进行异或的爆破

s = 'fsskryenvkm~jl{ejs}jwflzsnpgmifq{{j{|suhzrjppnx|qvixt~whu'
for i in range(255):
    res = ''
    for j in range(0, len(s)):
        temp = ord(s[j]) ^ i
        if 65 <= temp <= 90 or 97 <= temp <= 122:
            res += (chr(temp))
        else:
            break
    if len(res) == len(s):
        print(res)

然后根据提示是一个古典密码，查一下：

在这里插入图片描述

然后找到了自动秘钥的算法

DIC = "abcdefghijklmnopqrstuvwxyz"


def encrypt_autokey(string, key):
    ciphertext = ""

    key += string

    key_index = 0

    for i in string:

        if i not in DIC:
            ciphertext += i

        ciphertext += DIC[(DIC.index(i) + DIC.index(key[key_index])) % 26]

        key_index += 1

    return ciphertext


def decrypt_autokey(string, key):
    plaintext = ""

    key_index = 0

    for i in string:

        if i not in DIC:
            plaintext += i

        char = DIC[(DIC.index(i) - DIC.index(key[key_index])) % 26]

        key += char

        plaintext += char

        key_index += 1

    return plaintext