BUU_RE_[GXYCTF2019]luck_guy

64位,无壳

 

 字符串查找到一半的flag,双击跟进:

 

 在函数get_flag中,伪代码:

unsigned __int64 get_flag()
{
  unsigned int v0; // eax
  int i; // [rsp+4h] [rbp-3Ch]
  int j; // [rsp+8h] [rbp-38h]
  __int64 s; // [rsp+10h] [rbp-30h] BYREF
  char v5; // [rsp+18h] [rbp-28h]
  unsigned __int64 v6; // [rsp+38h] [rbp-8h]

  v6 = __readfsqword(0x28u);
  v0 = time(0LL);
  srand(v0);
  for ( i = 0; i <= 4; ++i )
  {
    switch ( rand() % 200 )
    {
      case 1:
        puts("OK, it's flag:");
        memset(&s, 0, 0x28uLL);
        strcat((char *)&s, f1);
        strcat((char *)&s, &f2);
        printf("%s", (const char *)&s);
        break;
      case 2:
        printf("Solar not like you");
        break;
      case 3:
        printf("Solar want a girlfriend");
        break;
      case 4:
        s = 0x7F666F6067756369LL;
        v5 = 0;
        strcat(&f2, (const char *)&s);
        break;
      case 5:
        for ( j = 0; j <= 7; ++j )
        {
          if ( j % 2 == 1 )
            *(&f2 + j) -= 2;
          else
            --*(&f2 + j);
        }
        break;
      default:
        puts("emmm,you can't find flag 23333");
        break;
    }
  }
  return __readfsqword(0x28u) ^ v6;
}

看到case1中,输出的flag由字符串和一个变量f2组成,现在求解f2

 case4给f2赋值,case5对f2处理

把s转换成字符串

再写脚本

s='\x7Ffo`guci'
flag=''
for i in range(8):
    if i%2==0:
        flag+=chr(ord(s[i])-2)
    else:
        flag+=chr(ord(s[i])-1)
print(flag[::-1])

最后倒过来是因为,

 

因为不熟大端小端,所以只好猜猜

flag

flag{do_not_hate_me}