source: branches/1.1dev/lib/Captcha.inc.php

<?php
/**
 * Captcha.inc.php
 * code by strangecode :: www.strangecode.com :: this document contains copyrighted information
 *
 * ASCII captcha system.
 *
 * @author  Quinn Comendant <quinn@strangecode.com>
 * @version 1.0 for codebase 1.x
-------------------------------------------------------------------------------------
// Example.

// Instantiate new Captcha. This automatically generates a new 4-digit captcha number.
$captcha = new Captcha();

// Validate incoming form submission.

<!-- HTML form for captcha -->
<label for="sc-captcha"><?php echo _("Reverse Turing Test") ?></label>
<p class="help"><?php echo _("Please type the following number to prove you are a human. This is a measure to prevent spam robots from submitting this form.") ?></p>
<pre style="font-size: 0.5em;"><?php $captcha->printAsciiNumber() ?></pre>
<?php $captcha->printForm() ?>
-------------------------------------------------------------------------------------
 */
class Captcha {

    var $secret_key = 'some random seed text';
    var $random_number;
    var $ascii_numbers = array(
        array(
            '  #####   ',
            ' ##   ##  ',
            '##     ## ',
            '##     ## ',
            '##     ## ',
            ' ##   ##  ',
            '  #####   ',
        ), array(
            '   ##   ',
            ' ####   ',
            '   ##   ',
            '   ##   ',
            '   ##   ',
            '   ##   ',
            ' ###### ',
        ), array(
            ' #######  ',
            '##     ## ',
            '       ## ',
            ' #######  ',
            '##        ',
            '##        ',
            '######### ',
        ), array(
            ' #######  ',
            '##     ## ',
            '       ## ',
            ' #######  ',
            '       ## ',
            '##     ## ',
            ' #######  ',
        ), array(
            '##        ',
            '##    ##  ',
            '##    ##  ',
            '##    ##  ',
            '######### ',
            '      ##  ',
            '      ##  ',
        ), array(
            '######## ',
            '##       ',
            '##       ',
            '#######  ',
            '      ## ',
            '##    ## ',
            ' ######  ',
        ), array(
            ' #######  ',
            '##     ## ',
            '##        ',
            '########  ',
            '##     ## ',
            '##     ## ',
            ' #######  ',
        ), array(
            '######## ',
            '##    ## ',
            '    ##   ',
            '   ##    ',
            '  ##     ',
            '  ##     ',
            '  ##     ',
        ), array(
            ' #######  ',
            '##     ## ',
            '##     ## ',
            ' #######  ',
            '##     ## ',
            '##     ## ',
            ' #######  ',
        ), array(
            ' #######  ',
            '##     ## ',
            '##     ## ',
            ' ######## ',
            '       ## ',
            '##     ## ',
            ' #######  ',
        )
    );
    
    /**
     * Constructor. Initialized new random number.
     *
     * @access  public
     * @author  Quinn Comendant <quinn@strangecode.com>
     * @since   20 Jan 2006 13:08:22
     */
    function __construct()
    {
        global $CFG;
        if (isset($CFG->signing_key)) {
            $this->secret_key = $CFG->signing_key;
        }
        $this->random_number = $this->_getRandomNumber();
    }

    /**
     * Print ASCII number.
     *
     * @access  public
     * @param   mixed   $num    Number to convert.
     * @return  string  ASCII-ized number
     * @author  Quinn Comendant <quinn@strangecode.com>
     * @since   07 Dec 2005 21:59:25
     */
    function getAsciiNumber($num)
    {
        if (preg_match('/[^\d]/', $num)) {
            logMsg(sprintf('Bad number: %s', $num), LOG_ERR, __FILE__, __LINE__);
            return false;
        }

        // Number must be an array of strings.
        $num = preg_split('// ', strval($num), -1, PREG_SPLIT_NO_EMPTY);

        // All chars must be same height.
        $output = '';
        $char_height = sizeof($this->ascii_numbers[0]);
        for ($i=0; $i<$char_height; $i++) {
            foreach ($num as $n) {
                $output .= $this->ascii_numbers[$n][$i];
            }
            $output .= "\n";
        }

        return $output;
    }

    /**
     * Prints the captcha ASCII numbers.
     *
     * @access  public
     * @author  Quinn Comendant <quinn@strangecode.com>
     * @since   07 Dec 2005 22:09:04
     */
    function printAsciiNumber()
    {
        $ascii = $this->getAsciiNumber($this->random_number);
        ?><pre name="sc-captcha" id="sc-captcha"><?php echo $ascii ?></pre><?php
    }

    /**
     * Prints a form to enter captcha, including the required hidden hash form.
     *
     * @access  public
     * @author  Quinn Comendant <quinn@strangecode.com>
     * @since   07 Dec 2005 22:09:04
     */
    function printForm()
    {
        $hash = $this->_getMD5key($this->random_number);
        ?>
        <input name="sc-captcha-input" id="sc-captcha-input" type="text" />
        <input name="sc-captcha-hash" id="sc-captcha-hash" type="hidden" value="<?php echo $hash ?>" />
        <?php
    }

    /**
     * Validate submitted number against ascii captcha.
     * Regenerate md5 hash from submitted captcha number and compare with posted hash.
     *
     * @access  public
     * @return  bool    True if number matches hash or false if EVIL ROBOT.
     * @author  Quinn Comendant <quinn@strangecode.com>
     * @since   07 Dec 2005 22:19:33
     */
    function valid()
    {
        $number = getFormData('sc-captcha-input');
        $hash = getFormData('sc-captcha-hash');

        if ('' == $number . $hash) {
            return false;
        }

        return $this->_getMD5key($number) == $hash;
    }

    /**
     * Generate random number 3-to-5 digits long.
     *
     * @access  private
     * @return  int         Generated number.
     * @author  Quinn Comendant <quinn@strangecode.com>
     * @since   07 Dec 2005 21:40:25
     */
    function _getRandomNumber()
    {
        return substr(strval(rand(10000, 99999)), 0, rand(3, 5));
    }

    /**
     * Generate md5 hash of number using secret key.
     *
     * @access  private
     * @param   string  $input  Input text to whack.
     * @return  string  md5 sum of input + seed
     * @author  Quinn Comendant <quinn@strangecode.com>
     * @since   07 Dec 2005 21:53:35
     */
    function _getMD5key($input)
    {
        return md5($this->secret_key . $input);
    }

}

?>