Code Elements: Very Simple Captcha

Very Simple Captcha or "Poor Man's Captcha"

This is a very simple way to implement a Captcha concept. It is less effective than say a generated on the fly image (using something like GD), but it is far better than using nothing at all.

Summary of Usage

In the PHP scripts that controls a page that requires a Captcha, simpley call the static function Captcha::generateCaptchaCode().
Then in the template of the page use Captcha::getHTMLCaptcha() to retrieve the HTML markups for the images representing the code.
Then on submision of the form with the captch, check the submitted value against the code in the session ($_SESSION['captcha_code'] by default)

Example Captcha Image

Simple Usage Example

Code for the Static Captcha class

/** * Very simple captcha solution. I had a client who's * server was not capable of generating images on the * fly (GD), so I just generated my own images (digits * 0-9) and use them. Not the most secure Captcha, but * better than nothing. * */ class Captcha { const CAPTCHA_IMAGE_DIR = "/images/captcha/"; // Range of characters available for captcha private static $available_captcha_chars = array( '1', '2', '3', '4', '5', '6', '7', '8', '9', '0' ); private static $captcha_image_map = array( 1 => '_0n3', 2 => '_tw0', 3 => '_thr33', 4 => '_f0ur', 5 => '_f1v3', 6 => '_51x', 7 => '_53v3n', 8 => '_31ght', 9 => '_n1n3', 0 => '_z3r0', ); /** * This is the key used to store the catcha in the $_SESSION. * * @var string */ private static $session_catcha_name = "captcha_code"; /** * Generate the random code and place it in the session * * @param int $number_of_captcha_chars * @return void */ public static function generateCaptchaCode($number_of_captcha_chars = 4) { // reset code $captcha_code = ''; $available_captcha_chars = self::$available_captcha_chars; $rand_max = count($available_captcha_chars) - 1; // loop through and generate the code letter by letter for ($i = 0; $i <$number_of_captcha_chars; $i++) { // get random index $char_index = rand(0, $rand_max); // append char to captcha string $captcha_code .= $available_captcha_chars[$char_index]; } // Set the current catcha code into the session $_SESSION[self::$session_catcha_name] = $captcha_code; return $captcha_code; } /** * For a given captcha code, returns its html * image representation * * @param string $captcha_code * @return string */ public static function getHTMLCaptcha ($captcha_code) { $HTML_output = "<div>\n"; for ($i=0;$i<strlen($captcha_code);$i++) src="'">\n"; } $HTML_output .= "</div>\n"; return $HTML_output; } /** * Verifiy that the given captcha matches that * in the session * * @param string $supplied_captcha * @return boolean */ public static function validateCaptcha($supplied_captcha) { return strtoupper($supplied_captcha)==$_SESSION[self::$session_catcha_name]; } }

Code Elements

Friday, January 26, 2007

Very Simple Captcha

Summary of Usage

Example Captcha Image

Simple Usage Example

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