栅栏密码解密优化

本文来源吾爱破解论坛

本帖最后由 Culaccino 于 2019-11-14 14:38 编辑

在做bugku逆向RE_Cirno的时候碰到一个栅栏发现解密的栅栏数和字符数对不上，于是自己优化了一下
writeup链接：https://blog.csdn.net/zhang644720213/article/details/100068670

[Python] 纯文本查看 复制代码

from math import ceil
 
def decode(flag,num):
    length = len(flag)  # flag的长度
    lines =  length // num # 判断共有几层并减一
    remainder = num * (lines + 1) - length  #相差的数量
 
    # 补全flag
    result = flag[:length-lines*remainder]
    for i in range(remainder-1,-1,-1):
        result += flag[length-(i+1)*lines:length-i*lines] + '*'
 
    # 还原flag
    lines += 1
    arr = [result[i:i+lines] for i in range(0,len(result),lines)]
    flag = ''
    for i in range(len(arr[0])):
        for j in arr:
            flag += j[i]
    return flag[:length]
 
def encode(flag,num):
    length = len(flag)
    lines = ceil(length / num)
    arr = [flag[i:i+num] for i in range(0,lines * num,num)]
    flag = ''
    for i in range(len(arr[0])):
        for j in arr:
            try:
                flag += j[i]
            except:
                pass
    return flag

if __name__ == "__main__":
    decode("fotl1eas0gvw{30Cr}1yrcnu",9)