public function testSign()
{
$keypair = KeyFactory::generateSignatureKeyPair();
$secretkey = $keypair->getSecretKey();
$publickey = $keypair->getPublicKey();
$signature = File::sign(__DIR__ . '/tmp/paragon_avatar.png', $secretkey);
$this->assertTrue(!empty($signature));
$this->assertTrue(File::verify(__DIR__ . '/tmp/paragon_avatar.png', $publickey, $signature));
}