BUUCTF--[FlareOn4]IgniteMe

代码分析

void __noreturn start()
{
  DWORD NumberOfBytesWritten; // [esp+0h] [ebp-4h]

  NumberOfBytesWritten = 0;
  hFile = GetStdHandle(0xFFFFFFF6);
  dword_403074 = GetStdHandle(0xFFFFFFF5);
  WriteFile(dword_403074, aG1v3M3T3hFl4g, 0x13u, &NumberOfBytesWritten, 0);
  sub_4010F0();
  if ( sub_401050() )
    WriteFile(dword_403074, aG00dJ0b, 0xAu, &NumberOfBytesWritten, 0);
  else
    WriteFile(dword_403074, aN0tT00H0tRWe7r, 0x24u, &NumberOfBytesWritten, 0);
  ExitProcess(0);
}

这里面分析好sub_4010F0和sub_401050函数就行了。

sub_4010F0函数

signed int sub_4010F0()
{
  unsigned int v0; // eax
  char Buffer[260]; // [esp+0h] [ebp-110h]
  DWORD NumberOfBytesRead; // [esp+104h] [ebp-Ch]
  unsigned int i; // [esp+108h] [ebp-8h]
  char v5; // [esp+10Fh] [ebp-1h]

  v5 = 0;
  for ( i = 0; i < 0x104; ++i )
    Buffer[i] = 0;
  ReadFile(hFile, Buffer, 0x104u, &NumberOfBytesRead, 0);
  for ( i = 0; ; ++i )
  {
    v0 = sub_401020(Buffer);
    if ( i >= v0 )
      break;
    v5 = Buffer[i];
    if ( v5 != 10 && v5 != 13 )
    {
      if ( v5 )
        byte_403078[i] = v5;
    }
  }
  return 1;
}

sub_401050函数

signed int sub_401050()
{
  int v0; // ST04_4
  int i; // [esp+4h] [ebp-8h]
  unsigned int j; // [esp+4h] [ebp-8h]
  char v4; // [esp+Bh] [ebp-1h]

  v0 = sub_401020(byte_403078);
  v4 = sub_401000();
  for ( i = v0 - 1; i >= 0; --i )
  {
    byte_403180[i] = v4 ^ byte_403078[i];
    v4 = byte_403078[i];
  }
  for ( j = 0; j < 0x27; ++j )
  {
    if ( byte_403180[j] != (unsigned __int8)byte_403000[j] )
      return 0;
  }
  return 1;
}

还是倒过来分析

sub_401050函数就是将字符串逆向做了异或操作之后，与已知字符串byte_403000对比。

sub_4010F0函数就是把我们输入字符串中的/r/n去掉。

脚本

# -*- coding:utf-8 -*-

arr2 = [0x0D,0x26,0x49,0x45,0x2A,0x17,0x78,0x44,0x2B,0x6C,0x5D,0x5E,0x45,0x12,0x2F,0x17,
0x2B,0x44,0x6F,0x6E,0x56,0x09,0x5F,0x45,0x47,0x73,0x26,0x0A,0x0D,0x13,0x17,0x48,
0x42,0x01,0x40,0x4D,0x0C,0x02,0x69]

arr1 = []
v4 = 4
for i in range(len(arr2)-1,-1,-1):
    arr1.append(arr2[i] ^ v4)
    v4 = arr1[-1]
print ('flag{'+''.join([chr(x) for x in arr1[::-1]])+'}')

get flag！

flag{R_y0u_H0t_3n0ugH_t0_1gn1t3@flare-on.com}