exeinfo分析，64位，

main函数：

void __fastcall __noreturn main(int a1, char **a2, char **a3)
{
  size_t v3; // rsi
  int i; // [rsp+3Ch] [rbp-54h]
  char s[36]; // [rsp+40h] [rbp-50h] BYREF
  int v6; // [rsp+64h] [rbp-2Ch]
  __int64 v7; // [rsp+68h] [rbp-28h]
  char v8[28]; // [rsp+70h] [rbp-20h] BYREF
  int v9; // [rsp+8Ch] [rbp-4h]

  v9 = 0;
  strcpy(v8, ":\"AL_RT^L*.?+6/46");
  v7 = 0x65626D61726168LL;
  v6 = 7;
  printf("Welcome to the RC3 secure password guesser.\n");
  printf("To continue, you must enter the correct password.\n");
  printf("Enter your guess: ");
  __isoc99_scanf("%32s", s);
  v3 = strlen(s);
  if ( v3 < strlen(v8) )
    sub_4007C0();
  for ( i = 0; i < strlen(s); ++i )
  {
    if ( i >= strlen(v8) )
      sub_4007C0();
    if ( s[i] != (char)(*((_BYTE *)&v7 + i % v6) ^ v8[i]) )
      sub_4007C0();
  }
  sub_4007F0();
}

函数sub_4007c0:

printf("Incorrect password!\n");

所以关键步就是循环中得第二个if：

if ( s[i] != (char)(*((_BYTE *)&v7 + i % v6) ^ v8[i]) )

那么key就是数组s

脚本：

#注意：if语句里面得char和BYTE要定义。

#include <stdio.h>
#include <string.h>
#define BYTE unsigned char
int main(int argc, char* argv[]) {
    unsigned int i;
    char v8[18] = ":\"AL_RT^L*.?+6/46";
    __int64 v7 = 28537194573619560;
    int v6 = 7;
    char s[18] = "";
    for (i = 0; i < strlen(v8); ++i) {
        s[i] = (char)(*((BYTE*)&v7 + i % v6)^v8[i]);
    }
    printf("%s\n", s);
    return 0;
}

得到：

RC3-2016-XORISGUD