BUUCTF--[WUSTCTF2020]level1

测试文件：https://lanzous.com/iclbz4d

 

代码分析

int __cdecl main(int argc, const char **argv, const char **envp)
{
  FILE *stream; // ST08_8
  signed int i; // [rsp+4h] [rbp-2Ch]
  char ptr[24]; // [rsp+10h] [rbp-20h]
  unsigned __int64 v7; // [rsp+28h] [rbp-8h]

  v7 = __readfsqword(0x28u);
  stream = fopen("flag", "r");
  fread(ptr, 1uLL, 0x14uLL, stream);
  fclose(stream);
  for ( i = 1; i <= 19; ++i )
  {
    if ( i & 1 )
      printf("%ld\n", (unsigned int)(ptr[i] << i));
    else
      printf("%ld\n", (unsigned int)(i * ptr[i]));
  }
  return 0;
}

对下标索引为奇数进行移位，偶数进行乘法。

 

脚本

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

a = [198,232,816,200,1536,300,6144,984,51200,570,92160,1200,565248,756,1474560,800,6291456,1782,65536000]

for i in range(19):
    if ((i+1) & 1):
        print(chr(a[i] >> (i+1)), end="")
    else:
        print (chr(a[i] // (i+1)),end="")

 

get flag！

flag{d9-dE6-20c}