ParagonIE\Halite\KeyFactory::save PHP Method

    public static function save($key, string $filename = '') : bool
    {
        if ($key instanceof KeyPair) {
            return self::saveKeyFile($filename, $key->getSecretKey()->getRawKeyMaterial());
        }
        return self::saveKeyFile($filename, $key->getRawKeyMaterial());
    }

 public function testFileStorage()
 {
     $filename = \tempnam(__DIR__ . '/tmp/', 'key');
     $key = KeyFactory::generateEncryptionKeyPair();
     KeyFactory::save($key, $filename);
     $copy = KeyFactory::loadEncryptionKeyPair($filename);
     $this->assertEquals($key->getPublicKey()->getRawKeyMaterial(), $copy->getPublicKey()->getRawKeyMaterial());
     \unlink($filename);
 }