In your home directory, you will have `.ovpn` files. These are the client configuration files. Download them from your server and connect using your favorite OpenVPN client.
If you have any question, head to the [FAQ](#faq) first.
Since 2016, the two scripts have diverged and are not alike anymore, especially under the hood. The main goal of the script was enhanced security. But since then, the script has been completely rewritten and a lot a features have been added. The script is only compatible with recent distributions though, so if you need to use a very old server or client, I advise using Nyr's script.
**A:** If possible, an official OpenVPN 2.4 client.
- Windows: [The official OpenVPN community client](https://openvpn.net/index.php/download/community-downloads.html).
- Linux: The `openvpn` package from your distribution. There is an [official APT repository](https://community.openvpn.net/openvpn/wiki/OpenvpnSoftwareRepos) for Debian/Ubuntu based distributions.
- macOS: [Tunnelblick](https://tunnelblick.net/).
- Android: [OpenVPN for Android](https://play.google.com/store/apps/details?id=de.blinkt.openvpn).
- iOS: I don't own an iOS device. Please let me know if you find a fully 2.4-compatible client.
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**Q:** The script has been updated since I installed OpenVPN. How do I update?
**A:** You can't. Managing updates and new features from the script would require way too much work. Your only solution is to uninstall OpenVPN and reinstall with the updated script.
You can, of course, it's even recommended, update the `openvpn` package with your package manager.
If you want more information about an option mentioned below, head to the [OpenVPN manual](https://community.openvpn.net/openvpn/wiki/Openvpn24ManPage). It is very complete.
Most of OpenVPN's encryption-related stuff is managed by [Easy-RSA](https://github.com/OpenVPN/easy-rsa). Defaults parameters are in the [vars.example](https://github.com/OpenVPN/easy-rsa/blob/v3.0.6/easyrsa3/vars.example) file.
By default, OpenVPN uses `BF-CBC` as the data channel cipher. Blowfish is an old (1993) and weak alogorithm. Even the official OpenVPN documentation admits it.
> The default is BF-CBC, an abbreviation for Blowfish in Cipher Block Chaining mode.
>
> Using BF-CBC is no longer recommended, because of its 64-bit block size. This small block size allows attacks based on collisions, as demonstrated by SWEET32. See https://community.openvpn.net/openvpn/wiki/SWEET32 for details.
>Security researchers at INRIA published an attack on 64-bit block ciphers, such as 3DES and Blowfish. They show that they are able to recover plaintext when the same data is sent often enough, and show how they can use cross-site scripting vulnerabilities to send data of interest often enough. This works over HTTPS, but also works for HTTP-over-OpenVPN. See https://sweet32.info/ for a much better and more elaborate explanation.
>
> OpenVPN's default cipher, BF-CBC, is affected by this attack.
Indeed, AES is today's standard. It's the fastest and more secure cipher available today. [SEED](https://en.wikipedia.org/wiki/SEED) and [Camellia](https://en.wikipedia.org/wiki/Camellia_(cipher)) are not vulnerable to date but are slower than AES and relatively less trusted.
> Of the currently supported ciphers, OpenVPN currently recommends using AES-256-CBC or AES-128-CBC. OpenVPN 2.4 and newer will also support GCM. For 2.4+, we recommend using AES-256-GCM or AES-128-GCM.
AES-256 is 40% slower than AES-128, and there isn't any real reason to use a 256 bits key over a 128 bits key with AES. (Source : [1](http://security.stackexchange.com/questions/14068/why-most-people-use-256-bit-encryption-instead-of-128-bit),[2](http://security.stackexchange.com/questions/6141/amount-of-simple-operations-that-is-safely-out-of-reach-for-all-humanity/6149#6149)). Moreover, AES-256 is more vulnerable to [Timing attacks](https://en.wikipedia.org/wiki/Timing_attack).
AES-GCM is an [AEAD cipher](https://en.wikipedia.org/wiki/Authenticated_encryption) which means it simultaneously provides confidentiality, integrity, and authenticity assurances on the data.
OpenVPN 2.4 added a feature called "NCP": *Negociable Crypto Parameters*. It means you can provide a cipher suite like with HTTPS. It is set to `AES-256-GCM:AES-128-GCM` by default and overrides the `--cipher` parameter when used with an OpenVPN 2.4 client. For the sake of simplicity, the script set both the `--cipher` and `--ncp-cipher` to the cipher chosen above.
> Authenticate data channel packets and (if enabled) tls-auth control channel packets with HMAC using message digest algorithm alg. (The default is SHA1 ). HMAC is a commonly used message authentication algorithm (MAC) that uses a data string, a secure hash algorithm, and a key, to produce a digital signature.
>
> If an AEAD cipher mode (e.g. GCM) is chosen, the specified --auth algorithm is ignored for the data channel, and the authentication method of the AEAD cipher is used instead. Note that alg still specifies the digest used for tls-auth.
> Add an additional layer of HMAC authentication on top of the TLS control channel to mitigate DoS attacks and attacks on the TLS stack.
>
> In a nutshell, --tls-auth enables a kind of "HMAC firewall" on OpenVPN's TCP/UDP port, where TLS control channel packets bearing an incorrect HMAC signature can be dropped immediately without response.
