private static function core($word,$iteration){
		/* rotate the 32-bit word 8 bits to the left */
		$word = self::rotate($word);
		/* apply S-Box substitution on all 4 parts of the 32-bit word */
		for ($i = 0; $i < 4; ++$i)
			$word[$i] = self::$sbox[$word[$i]];
		/* XOR the output of the rcon operation with i to the first part (leftmost) only */
		$word[0] = $word[0]^self::$Rcon[$iteration];
		return $word;
	}