SUCTF 2016 : dMd

这个题可以说是比较坑了（还不是我很弱...）

Linux跑一下：

要输密码

ida打开看看：

int __cdecl main(int argc, const char **argv, const char **envp)
{
  __int64 v3; // rax
  __int64 v4; // rax
  __int64 v5; // rax
  __int64 v6; // rax
  __int64 v7; // rax
  __int64 v8; // rax
  __int64 v9; // rax
  __int64 v10; // rax
  __int64 v11; // rax
  __int64 v12; // rax
  __int64 v13; // rax
  __int64 v14; // rax
  __int64 v15; // rax
  __int64 v16; // rax
  __int64 v17; // rax
  __int64 v18; // rax
  __int64 v19; // rax
  __int64 v20; // rax
  __int64 v21; // rax
  int result; // eax
  __int64 v23; // rax
  __int64 v24; // rax
  __int64 v25; // rax
  __int64 v26; // rax
  __int64 v27; // rax
  __int64 v28; // rax
  __int64 v29; // rax
  __int64 v30; // rax
  __int64 v31; // rax
  __int64 v32; // rax
  __int64 v33; // rax
  __int64 v34; // rax
  __int64 v35; // rax
  __int64 v36; // rax
  __int64 v37; // rax
  char v38; // [rsp+Fh] [rbp-71h]
  char v39; // [rsp+10h] [rbp-70h]
  char v40; // [rsp+20h] [rbp-60h]
  _BYTE *v41; // [rsp+28h] [rbp-58h]
  char v42; // [rsp+30h] [rbp-50h]
  unsigned __int64 v43; // [rsp+68h] [rbp-18h]

  v43 = __readfsqword(0x28u);
  std::operator<<<std::char_traits<char>>(&std::cout, "Enter the valid key!\n", envp);
  std::operator>><char,std::char_traits<char>>(&edata, &v42);
  std::allocator<char>::allocator((__int64)&v38);
  std::string::string(&v39, &v42, &v38);
  md5((MD5 *)&v40, (const std::string *)&v39);
  v41 = (_BYTE *)std::string::c_str((std::string *)&v40);
  std::string::~string((std::string *)&v40);
  std::string::~string((std::string *)&v39);
  std::allocator<char>::~allocator(&v38);
  if ( *v41 !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=
    || v41[] !=  )
  {
    v23 = std::operator<<<std::char_traits<char>>(&std::cout, 73LL);
    v24 = std::operator<<<std::char_traits<char>>(v23, 110LL);
    v25 = std::operator<<<std::char_traits<char>>(v24, 118LL);
    v26 = std::operator<<<std::char_traits<char>>(v25, 97LL);
    v27 = std::operator<<<std::char_traits<char>>(v26, 108LL);
    v28 = std::operator<<<std::char_traits<char>>(v27, 105LL);
    v29 = std::operator<<<std::char_traits<char>>(v28, 100LL);
    v30 = std::operator<<<std::char_traits<char>>(v29, 32LL);
    v31 = std::operator<<<std::char_traits<char>>(v30, 75LL);
    v32 = std::operator<<<std::char_traits<char>>(v31, 101LL);
    v33 = std::operator<<<std::char_traits<char>>(v32, 121LL);
    v34 = std::operator<<<std::char_traits<char>>(v33, 33LL);
    v35 = std::operator<<<std::char_traits<char>>(v34, 32LL);
    v36 = std::operator<<<std::char_traits<char>>(v35, 58LL);
    v37 = std::operator<<<std::char_traits<char>>(v36, 40LL);
    std::ostream::operator<<(v37, &std::endl<char,std::char_traits<char>>);
    result = ;
  }
  else
  {
    v3 = std::operator<<<std::char_traits<char>>(&std::cout, 84LL);
    v4 = std::operator<<<std::char_traits<char>>(v3, 104LL);
    v5 = std::operator<<<std::char_traits<char>>(v4, 101LL);
    v6 = std::operator<<<std::char_traits<char>>(v5, 32LL);
    v7 = std::operator<<<std::char_traits<char>>(v6, 107LL);
    v8 = std::operator<<<std::char_traits<char>>(v7, 101LL);
    v9 = std::operator<<<std::char_traits<char>>(v8, 121LL);
    v10 = std::operator<<<std::char_traits<char>>(v9, 32LL);
    v11 = std::operator<<<std::char_traits<char>>(v10, 105LL);
    v12 = std::operator<<<std::char_traits<char>>(v11, 115LL);
    v13 = std::operator<<<std::char_traits<char>>(v12, 32LL);
    v14 = std::operator<<<std::char_traits<char>>(v13, 118LL);
    v15 = std::operator<<<std::char_traits<char>>(v14, 97LL);
    v16 = std::operator<<<std::char_traits<char>>(v15, 108LL);
    v17 = std::operator<<<std::char_traits<char>>(v16, 105LL);
    v18 = std::operator<<<std::char_traits<char>>(v17, 100LL);
    v19 = std::operator<<<std::char_traits<char>>(v18, 32LL);
    v20 = std::operator<<<std::char_traits<char>>(v19, 58LL);
    v21 = std::operator<<<std::char_traits<char>>(v20, 41LL);
    std::ostream::operator<<(v21, &std::endl<char,std::char_traits<char>>);
    result = ;
  }
  return result;
}

可以看出来是先将输入的字符串进行md5加密 然后进行比对 正确就会输出一串字符

一开始我以为flag应该是输出的字符 于是：

a=[84,104,101,32,107,101,121,32,105,115,32,118,97,108,105,100,32,58,41]

s=''

for i in a:
    s+=chr(i)

print(s)

结果输出是：

The key is valid :)

okey....应该是考虑错了

那么就是md5这里：

b=[55,56,48,52,51,56,100,53,98,54,101,50,57,100,98,48,56,57,56,98,99,52,102,48,50,50,53,57,51,53,99,48]

s=''

for i in b:
    s+=chr(i)

print(s)

输出：

780438d5b6e29db0898bc4f0225935c0

这是md5加密后的值，把它解密：

输出是 grape

满心欢喜提交 错误......

仔细看一下这个md5的类型：

md5(md5($pass))

也就是加密了之后又进行了一遍md5加密的 所以grape是最初的字符串 780438d5b6e29db0898bc4f0225935c0是最终的密文

那么我们的key应该就是中间加密一次得到的字符串！

将 grape 加密一遍得到：

b781cbb29054db12f88f08c6e161c199

提交正确！