Problem: [柏鹭杯 2021]baby_python
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思路
- 解题大致思路
exeinfope分析:pyinstaller打包exe，直接使用pyinstxtractor-ng解包
注：看好多wp说用pyinstxtractor必须要用对应python3.7解包，而且要获取key，用脚本AES解密
pyinstxtractor-ng完全没有这个烦恼，直接一键解包+解密，(本人是3.10的环境一样解包成功)
使用pycdc反编译，baby.pyc显示
if __name__ == '__main__': main()
找到该import包，反编译得到python问题如下
# File: baby_core.pyc (Python 3.7) import hashlib def md5(s=None): m = hashlib.md5() m.update(s) return m.hexdigest().lower() def main(): secret = input('secret: ') if len(secret) != 48: return None if not None.isnumeric(): return None values = [] for i in range(0, 48, 3): values.append(int(secret[i:i + 3])) co = [ [158, 195, 205, 229, 213, 238, 211, 198, 190, 226, 135, 119, 145, 205, 113, 122], [234, 256, 185, 253, 244, 134, 102, 117, 190, 106, 131, 205, 198, 234, 162, 218], [164, 164, 209, 200, 168, 226, 189, 151, 253, 241, 232, 151, 193, 119, 226, 193], [213, 117, 151, 103, 249, 148, 103, 213, 218, 222, 104, 228, 100, 206, 218, 177], [217, 202, 126, 214, 195, 125, 144, 105, 152, 118, 167, 137, 171, 173, 206, 240], [160, 134, 131, 135, 186, 213, 146, 129, 125, 139, 174, 205, 177, 240, 194, 181], [183, 213, 127, 136, 136, 209, 199, 191, 150, 218, 160, 111, 191, 226, 154, 191], [247, 188, 210, 219, 179, 204, 155, 220, 215, 127, 225, 214, 195, 162, 214, 239], [108, 112, 104, 133, 178, 138, 110, 176, 232, 124, 193, 239, 131, 138, 161, 218], [140, 213, 142, 181, 179, 173, 203, 208, 184, 129, 129, 119, 122, 152, 186, 124], [105, 205, 124, 142, 175, 184, 234, 119, 195, 218, 141, 122, 202, 202, 190, 178], [183, 178, 256, 124, 241, 132, 163, 209, 204, 104, 175, 211, 196, 136, 158, 210], [224, 144, 189, 106, 177, 251, 206, 163, 167, 144, 208, 254, 117, 253, 100, 106], [251, 251, 136, 170, 145, 177, 175, 124, 193, 188, 193, 198, 208, 171, 151, 230], [143, 200, 143, 150, 243, 148, 136, 213, 161, 224, 170, 208, 185, 117, 189, 242], [234, 188, 226, 194, 248, 168, 250, 244, 166, 106, 113, 218, 209, 220, 158, 228] ] r = [472214, 480121, 506256, 449505, 433390, 435414, 453899, 536361, 423332, 427624, 440268, 488759, 469049, 484574, 480266, 522818] for i in range(16): v = 0 for j in range(16): v += co[i][j] * values[j] if v != r[i]: return None print('flag{ISEC-%s}' % md5(secret.encode()))
代码解释：
定义一个MD5函数，要输出小写结果
secret的长度为48，values列表的值是secret每3位为一个int
加密逻辑：
co为16×16矩阵
该行第n个值×values[n] 总和为v
v与r对应的值比较，即 r[n] = v = co[0]×values[0]+...+co[15]×values[15]
EXP
- 具体攻击代码
import hashlib def md5(s: bytes) -> str: m = hashlib.md5() m.update(s) return m.hexdigest().lower() co = [[158, 195, 205, 229, 213, 238, 211, 198, 190, 226, 135, 119, 145, 205, 113, 122], [ 234, 256, 185, 253, 244, 134, 102, 117, 190, 106, 131, 205, 198, 234, 162, 218], [ 164, 164, 209, 200, 168, 226, 189, 151, 253, 241, 232, 151, 193, 119, 226, 193], [ 213, 117, 151, 103, 249, 148, 103, 213, 218, 222, 104, 228, 100, 206, 218, 177], [ 217, 202, 126, 214, 195, 125, 144, 105, 152, 118, 167, 137, 171, 173, 206, 240], [ 160, 134, 131, 135, 186, 213, 146, 129, 125, 139, 174, 205, 177, 240, 194, 181], [ 183, 213, 127, 136, 136, 209, 199, 191, 150, 218, 160, 111, 191, 226, 154, 191], [ 247, 188, 210, 219, 179, 204, 155, 220, 215, 127, 225, 214, 195, 162, 214, 239], [ 108, 112, 104, 133, 178, 138, 110, 176, 232, 124, 193, 239, 131, 138, 161, 218], [ 140, 213, 142, 181, 179, 173, 203, 208, 184, 129, 129, 119, 122, 152, 186, 124], [ 105, 205, 124, 142, 175, 184, 234, 119, 195, 218, 141, 122, 202, 202, 190, 178], [ 183, 178, 256, 124, 241, 132, 163, 209, 204, 104, 175, 211, 196, 136, 158, 210], [ 224, 144, 189, 106, 177, 251, 206, 163, 167, 144, 208, 254, 117, 253, 100, 106], [ 251, 251, 136, 170, 145, 177, 175, 124, 193, 188, 193, 198, 208, 171, 151, 230], [ 143, 200, 143, 150, 243, 148, 136, 213, 161, 224, 170, 208, 185, 117, 189, 242], [ 234, 188, 226, 194, 248, 168, 250, 244, 166, 106, 113, 218, 209, 220, 158, 228]] r = [ 472214, 480121, 506256, 449505, 433390, 435414, 453899, 536361, 423332, 427624, 440268, 488759, 469049, 484574, 480266, 522818] s = Solver() values = [Int('v%d' % i) for i in range(16)] #print(values) for i in range(16): v = 0 for j in range(16): v += co[i][j] * values[j] s.add(v == r[i]) for j in range(16): s.add(values[j] > 0) s.check() answer = s.model() print(answer) #print([str(answer[each]) for each in values]) # [v13 = 103, v9 = 109, v12 = 152, v14 = 124, v10 = 244, v2 = 188, v0 = 113, v3 = 123, v15 = 165, v6 = 154, v7 = 241, v4 = 164, v8 = 163, v11 = 215, v1 = 201, v5 = 176] result = "".join([str(answer[each]) for each in values]) # print(result) # 113201188123164176154241163109244215152103124165 len(result) # 48 print('flag{ISEC-%s}' % md5(result.encode()))
定义values为16个未知数，正向写方程式解密
将v0——v15排列 md5加密即可