Seitenkanalangriff, aber wie?

  int compare_key () { 
      unsigned int len = strlen ( key_input ); 
      unsigned int correct_len = strlen ( correct_key );
      int i , random_time , false_key = 0; 
  
      unsigned int seed = getpid () + key_input ; 
      srand ( seed );  

      if ( len != correct_len ) 
          return 1; 
    
    
      for ( i = correct_len - 1; i >= 0; i - -) { 
          if ( key_input [i] != correct_key [i ]) { 
              usleep (500000) ; 
              false_key = 1; } 
       } 
              
      random_time = 500000 * ( rand () % 3);
      usleep ( random_time ); 
      return false_key ; 
}