BUUCTF xor RE

用Die查看发现无壳64位

用ida64 打开，F5反编译main函数

int __cdecl main(int argc, const char **argv, const char **envp)
{
  int i; // [rsp+2Ch] [rbp-124h]
  char __b[264]; // [rsp+40h] [rbp-110h] BYREF

  memset(__b, 0, 0x100uLL);
  printf("Input your flag:\n");
  get_line(__b, 256LL);
  if ( strlen(__b) != 33 )
    goto LABEL_7;
  for ( i = 1; i < 33; ++i )
    __b[i] ^= __b[i - 1];
  if ( !strncmp(__b, global, 0x21uLL) )
    printf("Success");
  else
LABEL_7:
    printf("Failed");
  return 0;
}

加密逻辑就是对一个长度为33的字符串每一个字符与前一位进行异或操作
现在重点就是global的值
双击globa，在汇编界面定位global的值
定位到这一串汇编代码

__cstring:0000000100000F6E
__cstring:0000000100000F6E ; Segment type: Pure data
__cstring:0000000100000F6E ; Segment permissions: Read/Execute
__cstring:0000000100000F6E __cstring       segment byte public 'DATA' use64
__cstring:0000000100000F6E                 assume cs:__cstring
__cstring:0000000100000F6E                 ;org 100000F6Eh
__cstring:0000000100000F6E aFKWOXZUPFVMDGH db 'f',0Ah              ; DATA XREF: __data:_global↓o
__cstring:0000000100000F6E                 db 'k',0Ch,'w&O.@',11h,'x',0Dh,'Z;U',11h,'p',19h,'F',1Fh,'v"M#D',0Eh,'g'
__cstring:0000000100000F6E                 db 6,'h',0Fh,'G2O',0

shift+E提取出global的值为

global=[0x66, 0x0A, 0x6B, 0x0C, 0x77, 0x26, 0x4F, 0x2E, 0x40, 0x11, 
  0x78, 0x0D, 0x5A, 0x3B, 0x55, 0x11, 0x70, 0x19, 0x46, 0x1F, 
  0x76, 0x22, 0x4D, 0x23, 0x44, 0x0E, 0x67, 0x06, 0x68, 0x0F, 
  0x47, 0x32, 0x4F, 0x00]

简单写个脚本得到flag

点击查看代码

a = [0x66, 0x0A, 0x6B, 0x0C, 0x77, 0x26, 0x4F, 0x2E, 0x40, 0x11, 
  0x78, 0x0D, 0x5A, 0x3B, 0x55, 0x11, 0x70, 0x19, 0x46, 0x1F, 
  0x76, 0x22, 0x4D, 0x23, 0x44, 0x0E, 0x67, 0x06, 0x68, 0x0F, 
  0x47, 0x32, 0x4F, 0x00]
for i in range(len(a)):
    if(type(a[i])==int): a[i]=chr(a[i])
a = "".join(a)
flag="f"
for i in range(1,len(a)):
    flag+=chr(ord(a[i]) ^ ord(a[i-1]))
print(flag)

flag{QianQiuWanDai_YiTongJiangHu}