SUCTF-Crypto-Magic

最新推荐文章于 2025-05-24 11:32:59 发布

T1an5t

最新推荐文章于 2025-05-24 11:32:59 发布

阅读量1.1k

点赞数

CC 4.0 BY-SA版权

分类专栏： Crypto

本文链接：https://blog.youkuaiyun.com/qq_39153247/article/details/80595467

本文总结了SUCTF中的一道Crypto题目——Magic，详细分析了题目所给的源码、cipher和magic文件。通过将magic视为256×256的0/1矩阵，key视为256行1列的0/1矩阵，以及cipher也是一个256行1列的矩阵，利用矩阵运算法则求解。通过Sage脚本成功求出magic的逆矩阵，实现解密过程，进一步理解了希尔密码的工作原理。

题目在官方网站还可以下载得到，这里比赛后总结一下WP（虽然比赛的时候并没有做上）

题目源码：

from flag import flag

def getMagic():
    magic = []
    with open("magic.txt") as f:
        while True:
            line = f.readline()
            if (line):
                line = int(line, 16)
                magic.append(line)
                # print bin(line)[2:]
            else:
                break
    return magic

def playMagic(magic, key):
    cipher = 0
    for i in range(len(magic)):
        cipher = cipher << 1
        t = magic[i] & key
        c = 0
        while t:
            c = (t & 1) ^ c
            t = t >> 1
        cipher = cipher ^ c
    return cipher

def main():
    key = flag[5:-1]
    assert len(key) == 32
    key = key.encode("hex")
    key = int(key, 16)
    magic = getMagic()
    cipher = playMagic(magic, key)
    cipher = hex(cipher)[2:-1]
    with open("cipher.txt", "w") as f:
        f.write(cipher + "\n")

if __name__ == "__main__"