private function convertPrivateKeyToRsaKey(PrivateKey $privateKey)
{
$key = new XMLSecurityKey(XMLSecurityKey::RSA_1_5, array('type' => 'private'));
$passphrase = $privateKey->getPassphrase();
if ($passphrase) {
$key->passphrase = $passphrase;
}
$key->loadKey($privateKey->getKeyAsString());
return $key;
}