/**
* Performs the first step of a Diffie-Hellman key exchange by generating
* private and public DH values based on given prime number $p and
* generator $g. Both sides of key exchange MUST have the same prime number
* and generator. In this case they will able to create a random shared
* secret that is never send from one to the other.
*
* @param string $p prime number in binary representation
* @param string $g generator in binary representation
* @param string $priv_key private key in binary representation
* @return mixed
*/
public static function createDhKey($p, $g, $priv_key = null)
{
if (function_exists('openssl_dh_compute_key')) {
$dh_details = array('p' => $p, 'g' => $g);
if ($priv_key !== null) {
$dh_details['priv_key'] = $priv_key;
}
return openssl_pkey_new(array('dh' => $dh_details));
} else {
$bn_p = self::binToBigNum($p);
$bn_g = self::binToBigNum($g);
if ($priv_key === null) {
$priv_key = self::randomBytes(OpenID::strlen($p));
}
$bn_priv_key = self::binToBigNum($priv_key);
if (extension_loaded('gmp')) {
$bn_pub_key = gmp_powm($bn_g, $bn_priv_key, $bn_p);
} else {
if (extension_loaded('bcmath')) {
$bn_pub_key = bcpowmod($bn_g, $bn_priv_key, $bn_p);
}
}
$pub_key = self::bigNumToBin($bn_pub_key);
return array('p' => $bn_p, 'g' => $bn_g, 'priv_key' => $bn_priv_key, 'pub_key' => $bn_pub_key, 'details' => array('p' => $p, 'g' => $g, 'priv_key' => $priv_key, 'pub_key' => $pub_key));
}
}
