static function savePublicKey(BigInteger $n, BigInteger $e)
{
$publicExponent = $e->toBytes(true);
$modulus = $n->toBytes(true);
// from <http://tools.ietf.org/html/rfc4253#page-15>:
// string "ssh-rsa"
// mpint e
// mpint n
$RSAPublicKey = pack('Na*Na*Na*', strlen('ssh-rsa'), 'ssh-rsa', strlen($publicExponent), $publicExponent, strlen($modulus), $modulus);
$RSAPublicKey = 'ssh-rsa ' . Base64::encode($RSAPublicKey) . ' ' . self::$comment;
return $RSAPublicKey;
}