/**
  * Load a keypair from a file
  * 
  * @param string $filePath
  * @param int $type
  * @return KeyPair
  * 
  * @throws CryptoException\InvalidFlags
  */
 public static function fromFile($filePath, $type = Key::CRYPTO_SIGN)
 {
     $keys = SignatureSecretKey::fromFile($filePath, $type | Key::ASYMMETRIC | Key::ENCRYPTION);
     return new SignatureKeyPair(...$keys);
 }