攻防世界 reverse hackme

hackme XCTF 3rd-GCTF-2017

__int64 __fastcall sub_400F8E(__int64 a1, __int64 a2)
{
  char input[136]; // [rsp+10h] [rbp-B0h]
  int v4; // [rsp+98h] [rbp-28h]
  char v5; // [rsp+9Fh] [rbp-21h]
  int v6; // [rsp+A0h] [rbp-20h]
  unsigned __int8 c; // [rsp+A6h] [rbp-1Ah]
  char b; // [rsp+A7h] [rbp-19h]
  int index; // [rsp+A8h] [rbp-18h]
  int j; // [rsp+ACh] [rbp-14h]
  int temp; // [rsp+B0h] [rbp-10h]
  int k; // [rsp+B4h] [rbp-Ch]
  _BOOL4 sign; // [rsp+B8h] [rbp-8h]
  int i; // [rsp+BCh] [rbp-4h]

  print_407470((__int64)"Give me the password: ", a2);
  scanf_4075A0((__int64)"%s", input);
  for ( i = 0; input[i]; ++i )
    ;
  sign = i == 22;                               // 输入22位
  k = 10;                                       // 只验证了10个数
  do
  {
    index = (signed int)f_406D90() % 22;        // 生成随机数
    temp = 0;
    b = byte_6B4270[index];
    c = input[index];
    v6 = index + 1;
    j = 0;
    while ( j < v6 )
    {
      ++j;
      temp = 0x6D01788D * temp + 0x3039;     
    }
    v5 = temp ^ c;
    if ( b != ((unsigned __int8)temp ^ c) )
      sign = 0;
    --k;
  }
  while ( k );
  if ( sign )
    v4 = print_407470((__int64)"Congras
");
  else
    v4 = print_407470((__int64)"Oh no!
");
  return 0LL;
}

程序流程：

验证输入22位-->生成随机数验证10位数

wp:

bs=[0x5F, 0xF2, 0x5E, 0x8B, 0x4E, 0x0E, 0xA3, 0xAA, 0xC7, 0x93,
  0x81, 0x3D, 0x5F, 0x74, 0xA3, 0x09, 0x91, 0x2B, 0x49, 0x28,
  0x93, 0x67]
flag=[0 for i in range(22)]
for index in range(22):
    b=bs[index]
    temp=0
    for i in range(index+1):
        temp=(0x6D01788D * temp + 0x3039)
    flag[index]=(temp^b)&0xff
print(''.join(map(chr,flag)))

flag{d826e6926098ef46}