这次跟校队的几位同届的大师傅一起打的，师傅们都很强，又是被师傅们带着冲的一集。可惜我们缺个pwn手，这次的pwn从解题人数来看应该不难，但是我们一题都没做。。。

Writeup部分

Writeup

复现部分

不懂的还是太多了，好好复现一下吧。

Misc

Just_F0r3n51Cs

这题当时是找到了第三第四个flag，第一个flag找到了密钥但是没找到密文。

flag1

在桌面上可以找到beginning.pcapng

image-20241207185904257

追踪一下http流可以看到传输了一张jpg图片，保存下来

image-20241207190018698

图片结尾有一串base64

image-20241207190302519

解出来提示oursecret，用oursecret提取得到hidden.txt

image-20241207190353388
image-20241207190505330

内容如下

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ECB's key is
N11c3TrYY6666111
记得给我秋秋空间点赞

查看流量包中的oicq流，可以看到一个QQ号

image-20241207190631379

看一下其空间，找到密文

FEFD121B2F9676AB28DFE7834E11BB28

image-20241207190927635
flag2

找到SYSTEM，右键解析注册表

image-20241207191051755

查看环境变量，找到第二个flag存放的路径，前往将其导出

image-20241207191309431

文件名字叫2，但是从特征不难发现这是个压缩包，有注释。

image-20241207191511072

根据要求找到相关信息，得到密码D0g3xGC_Windows_7_Ultimate_115.0

image-20241207192038615
image-20241207192104491

base85

image-20241207192304255
flag3

不难找到original.zip，到处都是它的痕迹。同时在图片文件夹下可以找到一张特殊的图片。

image-20241207192522212

压缩包有注释

image-20241207192609657

根据要求找到相关信息，得到密码qwe123!@#_Y0u_f1Nd_m3_233

image-20241207192723500
image-20241207192801229
image-20241207192901376

根据水印图片的名字CatWaterMark_666.png可知，用github上的这个工具提取盲水印，参数为666

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python decode.py Original.png CatWaterMark_666.png output.png 6 6 6
image-20241207193442527
flag4

不难找到flag4.zip，到处都是它的痕迹。

image-20241207193653243

flag4.zip里面有个python打包的exe和一个加密的bin文件，python逆向一下

image-20241207194149584
image-20241207194230130 
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# uncompyle6 version 3.9.1
# Python bytecode version base 3.8.0 (3413)
# Decompiled from: Python 3.10.11 (tags/v3.10.11:7d4cc5a, Apr  5 2023, 00:38:17) [MSC v.1929 64 bit (AMD64)]
# Embedded file name: enc_png.py

def xor_encrypt(data, key):
    encrypted_data = bytearray()
    for i in range(len(data)):
        encrypted_data.append(data[i] ^ key[i % len(key)])
    else:
        return encrypted_data

def read_file(file_path):
    with open(file_path, "rb") as file:
        data = file.read()
    return data

def write_file(file_path, data):
    with open(file_path, "wb") as file:
        file.write(data)

def encrypt_file(input_file_path, output_file_path, key):
    data = read_file(input_file_path)
    encrypted_data = xor_encrypt(data, key)
    write_file(output_file_path, encrypted_data)

if __name__ == "__main__":
    key = b'GCcup_wAngwaNg!!'
    input_file = "flag4.png"
    encrypted_file = "flag4_encrypted.bin"
    encrypt_file(input_file, encrypted_file, key)

# okay decompiling enc_png.pyc

什么都不用改就能解密：

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def xor_decrypt(data, key):
    encrypted_data = bytearray()
    for i in range(len(data)):
        encrypted_data.append(data[i] ^ key[i % len(key)])
    else:
        return encrypted_data

def read_file(file_path):
    with open(file_path, "rb") as file:
        data = file.read()
    return data

def write_file(file_path, data):
    with open(file_path, "wb") as file:
        file.write(data)

def decrypt_file(input_file_path, output_file_path, key):
    data = read_file(input_file_path)
    decrypted_data = xor_decrypt(data, key)
    write_file(output_file_path, decrypted_data)

if __name__ == "__main__":
    key = b'GCcup_wAngwaNg!!'
    input_file = "flag4_encrypted.bin"
    decrypted_file = "flag4.png"
    decrypt_file(input_file, decrypted_file, key)

flag4.png:

img

合起来

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D0g3xGC{Y0u_h4V3_f0und_7H3_F1N4L_s3CR3t_0F_Th15_F0R3N51c5_Ch4Ll3N93}

eZ_Steg0

图片名叫01.png，写个python脚本遍历每个像素，黑色记为0，白色记为1，输出二进制字符串

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from PIL import Image
def image_to_binary_string(image_path, threshold=127):
    with Image.open(image_path) as img:
        img = img.convert('L')
        binary_string = ""
        for y in range(img.height):
            for x in range(img.width):
                pixel_value = img.getpixel((x, y))
                if pixel_value < threshold:
                    binary_string += "0" 
                else:
                    binary_string += "1" 
    return binary_string.strip() 
image_path = '01.png' 
result_string = image_to_binary_string(image_path)
print(result_string)

cyberchef转换一下，删去一些0以后发现结尾有倒着的png头

image-20241209184653844

处理一下保存为png

image-20241209184747610
image-20241209185016483

这就是key.zip的密码。解压得到的key开头有段base64

image-20241209185254500
image-20241209185317446

提示了这是一个stl文件，删去开头的base64，修改后缀名为.stl，用这个网站查看，即可看到key

image-20241209185656525

用这个key去对不知道是什么东西的flag文件异或一下，可以得到一个wav文件

image-20241209185954584

提取音频lsb隐写，得到flag

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import wave
song = wave.open("download.wav", mode='rb')
# Convert audio to byte array
frame_bytes = bytearray(list(song.readframes(song.getnframes())))

# Extract the LSB of each byte
extracted = [frame_bytes[i] & 1 for i in range(len(frame_bytes))]
# Convert byte array back to string
string = "".join(chr(int("".join(map(str,extracted[i:i+8])),2)) for i in range(0,len(extracted),8))
# Cut off at the filler characters
decoded = string.split("###")[0]

# Print the extracted text
print("Sucessfully decoded: "+decoded)
song.close()
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D0g3xGC{U_4rE_4_WhI2_4t_Ste9An09r4pHY}