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8 years ago
This openssl_spki_* funcs are very usefull to use with <keygen/> tag in html5.

Example:

<?php
session_start();

// form submitted... (?)
if(isset($_POST['security']))
{
    // If true, the send from <keygen/> is valid and you can
    // test the challenge too
    if(openssl_spki_verify($_POST['security']))
    {
        // Gets challenge string
        $challenge = openssl_spki_export_challenge($_POST['security']);

        // If true... you are not trying to trick it.
        // If user open 2 windows to prevent data lost from a "mistake" or him just press "back" button
        //  and re-send last data... you can handle it using something like it.
        if($challenge == $_SESSION['lastForm'])
        {
            echo 'Ok, this one is valid.', '<br><br>';
        }
        else
        {
            echo 'Nice try... nice try...', '<br><br>'; 
        }
    }

}

// If you open two window, the challenge won't match!
$_SESSION['lastForm'] = hash('md5', microtime(true));

?>

<!DOCTYPE html>
<html>
<body>

<form action="/https/www.php.net/index.php" method="post">
  Encryption: <keygen name="security" keytype="rsa" challenge="<?php echo $_SESSION['lastForm']; ?>"/>
  <input type="submit">
</form>

</body>
</html>
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