Solving Root-Me XORed Picture Challenge

Root-me.c

#include <stdio.h>
#define KEY_LENGTH 6 
/*
* Title: Solving Root-Me XORed Picture Challenge
* Author: Osanda Malith Jayathissa (@OsandaMalith)
* Website: https://osandamalith.wordpress.com
*/
int main() {
  
  FILE *fpIn, *fpOut;
  unsigned char key[KEY_LENGTH] = {'f', 'a', 'l', 'l', 'e', 'n'};
  int enc = 0;
  
  fpIn = fopen("ch3.bmp", "rb");
  fpOut = fopen("flag.bmp", "wb");
  
  for (size_t i = 0; fscanf(fpIn, "%c", &enc) != EOF; ++i) 
  fprintf(fpOut, "%c", enc ^ key[i % KEY_LENGTH]);   
   
  fclose(fpIn);
  fclose(fpOut);
    
  return 0;
}