Blog K

<?php
 
class Verifier {
 
/*
 * Private Properties
 */
 
	// operators available to the class
	private static $operators = array(
		array('plus', '+'), array('minus', '-'), array('times', '*')
	);
 
	// numbers available to the class
	private static $numbers = array('zero', 'one', 'two', 'three', 'four', 'five');
 
/*
 * Private Methods
 */
 
	// return an operator from the list, selected by
	// either index, symbol, or name.
	private static function getOperator($op) {
		if (is_int($op)) return self::$operators[$op];
		foreach (self::$operators as $operator) {
			if ($operator[0] == $op || $operator[1] == $op) {
				return $operator;
			}
		}
		return null;
	}
 
	// return a random operator from the list.
	private static function randOperator() {
		$rand = rand(1, count(self::$operators)) - 1;
		return self::$operators[$rand];
	}
 
	// store all of the operator symbols in a passed variable.
	private static function getOperators(&$ops) {
		$ops = array();
		foreach (self::$operators as $operator) {
			$ops[] = $operator[1];
		}
	}
 
}
 
?>

public static function make_equation() {
	// we will store the final equation in a session
	// variable so we can check it later
	session_start();
	// generate our random elements
	$n1 = rand(0, count(self::$numbers) - 1);
	$n2 = rand(0, count(self::$numbers) - 1);
	$op = self::randOperator();
	// build the equation in a PHP format and
	// store it for checking later
	$equation = $n1 . ' ' . $op[1] . ' ' . $n2;
	$_SESSION['FormVerify'] = $equation;
	// return the equation, but using the number
	// and operator names
	return self::$numbers[$n1] . ' ' . $op[0] . ' ' . self::$numbers[$n2];
}

private static function solveEquation($equation) {
	self::getOperators($ops);
	// use a regular expression to make sure the equation is
	// in the expected format to protect against the posiblity
	// of evaling "bad" code
	$equationRegex = '/([0-9]+)\s(\\' . implode('|\\', $ops) . ')\s([0-9]+)/';
	preg_match($equationRegex, $equation, $match);
	$answer = false;
	// if the equation is good, calculate and return the answer
	if ($match[0]) eval('$answer='.$equation.';');
	return $answer;
}
 
public static function check_equation($value) {
	// read the equation from the session variable
	session_start();
	$eq = $_SESSION['FormVerify'];
	// check for a match and return a bool
	return (self::solveEquation($eq) == $value);
}

<?php
 
class Verifier {
 
/*
 * Private Properties
 */
 
	// operators available to the class
	private static $operators = array(
		array('plus', '+'), array('minus', '-'), array('times', '*')
	);
 
	// numbers available to the class
	private static $numbers = array('zero', 'one', 'two', 'three', 'four', 'five');
 
/*
 * Private Methods
 */
 
	// return an operator from the list, selected by
	// either index, symbol, or name.
	private static function getOperator($op) {
		if (is_int($op)) return self::$operators[$op];
		foreach (self::$operators as $operator) {
			if ($operator[0] == $op || $operator[1] == $op) {
				return $operator;
			}
		}
		return null;
	}
 
	// return a random operator from the list.
	private static function randOperator() {
		$rand = rand(1, count(self::$operators)) - 1;
		return self::$operators[$rand];
	}
 
	// store all of the operator symbols in a passed variable.
	private static function getOperators(&$ops) {
		$ops = array();
		foreach (self::$operators as $operator) {
			$ops[] = $operator[1];
		}
	}
 
	private static function solveEquation($equation) {
		self::getOperators($ops);
		$equationRegex = '/([0-9]+)\s(\\' . implode('|\\', $ops) . ')\s([0-9]+)/';
		preg_match($equationRegex, $equation, $match);
		$answer = false;
		if ($match[0]) eval('$answer='.$equation.';');
		return $answer;
	}
 
/*
 * Public Methods
 */
 
	public static function make_equation() {
		session_start();
		$n1 = rand(0, count(self::$numbers) - 1);
		$n2 = rand(0, count(self::$numbers) - 1);
		$op = self::randOperator();
		$equation = $n1 . ' ' . $op[1] . ' ' . $n2;
		$_SESSION['FormVerify'] = $equation;
		return self::$numbers[$n1] . ' ' . $op[0] . ' ' . self::$numbers[$n2];
	}
 
	public static function check_equation($value) {
		session_start();
		$eq = $_SESSION['FormVerify'];
		return (self::solveEquation($eq) == $value);
	}
 
}
 
/*
 * USAGE
 */
 
	// generate a test equation
	$equation = Verifier::make_equation();
 
	// and check the answer is correct in your validation script
	if (Verifier::check_equation($_POST['user_response'])) {
		die('Hello, Human :)');
	} else {
		die('Go Away, Evil Computer!');
	}
 
?>