BMZCTF：2020sdnisc-左上角的秘密

最新推荐文章于 2022-04-24 19:36:08 发布

末初mochu7

于 2020-12-14 22:53:49 发布

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分类专栏： CTF_MISC_Writeup

本文链接：https://blog.csdn.net/mochu7777777/article/details/111187726

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http://bmzclub.cn/challenges#2020sdnisc-%E5%B7%A6%E4%B8%8A%E8%A7%92%E7%9A%84%E7%A7%98%E5%AF%86

在这里插入图片描述
enc.py

# encoding=utf-8
flag_enc = open("flag_enc.hex", "wb")
def file_encode(flag):
    i = 1
    while True:
        byte_str = flag.read(1)
        if (byte_str == b''):
            exit()
        byte_str = hex_encode(byte_str)
        file_write(flag_enc, byte_str)
        # print(byte_str, end="")
        i = i + 1

def hex_encode(byte_str):

    tmp = int.from_bytes(byte_str, byteorder="big")
    if (tmp % 2 == 0):
        tmp = (tmp + 1) ^ 128
    else:
        tmp = (tmp - 1) ^ 128
    tmp = bytes([tmp])
    return tmp

def file_write(flag_enc, byte_str):
    flag_enc.write(byte_str)


if __name__ == '__main__':
    with open("./flag.png", "rb") as flag:
        file_encode(flag)
    flag_enc.close()

flag_enc.hex
在这里插入图片描述
逆向处理一下数据

with open('flag.png','wb') as flag:
    with open('flag_enc.hex','rb') as f:
        for i in f.read():
            if (i % 2 == 0):
                i = (i + 1) ^ 128
            else:
                i = (i - 1) ^ 128
            i = bytes([i])
            flag.write(i)

得到flag.png

在这里插入图片描述
使用PS打开，查看左上角

依此取色块色号的十六进制

Python处理

from base64 import *

base64str = ''
with open('data.txt') as f:
    for i in f.readlines():
        i = chr(int(i[2:4],16))
        base64str = base64str + i
flag = b64decode(base64str)
print(base64str)
print(flag)

在这里插入图片描述

flag{c6e4c99a6388c5d2a9ae6ef6a843cea6}

末初mochu7

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BMZCTF：2020sdnisc-左上角的秘密

http://bmzclub.cn/challenges#2020sdnisc-%E5%B7%A6%E4%B8%8A%E8%A7%92%E7%9A%84%E7%A7%98%E5%AF%86enc.py# encoding=utf-8flag_enc = open("flag_enc.hex", "wb")def file_encode(flag): i = 1 while True: byte_str = flag.read(1) if (byte
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