openvpn-install/README.md

openvpn-install

OpenVPN installer for Debian, Ubuntu, Fedora, CentOS and Arch Linux.

This script will let you setup your own secure VPN server in just a few seconds.

Usage

First, get the script and make it executable :

wget https://raw.githubusercontent.com/Angristan/openvpn-install/master/openvpn-install.sh
chmod +x openvpn-install.sh

Then run it :

./openvpn-install.sh

You need to run the script as root and have the TUN module enabled.

The first time you run it, you'll have to follow the assistant and answer a few questions to setup your VPN server.

When OpenVPN is installed, you can run the script again, and you will get the choice to :

• Add a client
• Remove a client
• Uninstall OpenVPN

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 first.

Features

• Installs and configures a ready-to-use OpenVPN server
• Iptables rules and forwarding managed in a seamless way
• If needed, the script can cleanly remove OpenVPN, including configuration and iptables rules
• Customisable encryption settings, enhanced default settings (see Security and Encryption below)
• OpenVPN 2.4 features, mainly encryption improvements (see Security and Encryption below)
• Varietey of DNS resolvers to be pushed to the clients
• Choice to use a self-hosted resolver with Unbound (supports already existing Unboud installations)
• Choice between TCP and UDP
• NATed IPv6 support
• Compression disabled by default to prevent VORACLE. LZ4 and LZ0 algorithms available otherwise.
• Unprivileged mode: run as nobody/nogroup
• Block DNS leaks on Windows 10
• Randomised server certificate name
• Choice to protect clients with a password (private key encryption)
• Many other little things!

Compatibility

The script supports these OS and architectures:

	i386	amd64	armhf	arm64
Arch Linux	❔	✅	❔	❔
CentOS 7	❔	✅	❌	❌
Debian 8	✅	✅	❌	❌
Debian 9	❌	✅	✅	✅
Fedora 27	❔	✅	❔	❔
Fedora 28	❔	✅	❔	❔
Ubuntu 16.04	✅	✅	❌	❌
Ubuntu 18.04	❌	✅	✅	✅

To be noted:

• It should work on Debian 8+ and Ubuntu 16.04+. But versions not in the table above are not officially supported.
• The script requires systemd.
• The script is regularly tested against amd64 only.

Fork

This script is based on the great work of Nyr and its contributors.

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.

FAQ

Q: Which provider do you recommend?

A: I recommend these:

• Vultr: Worldwide locations, IPv6 support, starting at $3.50/month
• PulseHeberg: France, unlimited bandwidth, starting at €3/month
• Digital Ocean: Worldwide locations, IPv6 support, starting at $5/month

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Q: Which OpenVPN client do you recommend?

A: If possible, an official OpenVPN 2.4 client.

• Windows: The official OpenVPN community client.
• Linux: The openvpn package from your distribution. There is an official APT repository for Debian/Ubuntu based distributions.
• macOS: Tunnelblick.
• Android: OpenVPN for Android.
• 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.

---

Q: How do I check for DNS leaks?

A: Go to dnsleaktest.com or ipleak.net with your browser. Only your server's IP should show up.

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Q: Is there an OpenVPN documentation?

A: Yes, please had to the OpenVPN Manual, which references all the options.

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Q: Can I use an OpenVPN 2.3 client?

A: Yes. I really recommend using an up-to-date client, but if you really need it, choose the following options:

• No compression or LZ0
• RSA certificate
• DH Key
• AES CBC
• tls-auth

If your client is <2.3.3, remove tls-version-min 1.2 from your /etc/openvpn/server.conf and .ovpn files.

---

Q: IPv6 is not working on my Hetzner VM

A: This an issue on their side. See issue #295.

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Security and Encryption

OpenVPN's default settings are pretty weak regarding encryption. This script aims to improve that.

OpenVPN 2.4 was a great update regarding encryption. It added support for ECDSA, ECDH, AES GCM, NCP and tls-crypt.

If you want more information about an option mentioned below, head to the OpenVPN manual. It is very complete.

Most of OpenVPN's encryption-related stuff is managed by Easy-RSA. Defaults parameters are in the vars.example file.

Compression

By default, OpenVPN doesn't enable compression. This script provides support for LZ0 and LZ4 algorthms, the latter being more efficient.

However, it is discouraged to use compression since it since the VORACLE attack makes use of it.

TLS version

OpenVPN accepts TLS 1.0 by default, which is nearly 20 years old.

With tls-version-min 1.2 we enforce TLS 1.2, which the best protocol available currently for OpenVPN.

TLS 1.2 is supported since OpenVPN 2.3.3.

Certificate

OpenVPN uses an RSA certificate with a 2048 bits key by default.

OpenVPN 2.4 added support for ECDSA. Elliptic curve cryptography is faster, lighter and more secure.

This script provides:

• ECDSA: prime256v1/secp384r1/secp521r1 curves
• RSA: 2048/3072/4096 bits keys

It defaults to ECDSA with prime256v1.

OpenVPN uses SHA-256 as the signature hash by default, and so does the script. It provides no other choice as of now.

Data channel

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 and Camellia 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 : 1,2). Moreover, AES-256 is more vulnerable to Timing attacks.

AES-GCM is an AEAD cipher which means it simultaneously provides confidentiality, integrity, and authenticity assurances on the data.

The script supports the following ciphers:

• AES-128-GCM
• AES-192-GCM
• AES-256-GCM
• AES-128-CBC
• AES-192-CBC
• AES-256-CBC

And defaults to AES-128-GCM.

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.

Control channel

OpenVPN 2.4 will negotiate the best cipher available by default (e.g ECDHE+AES-256-GCM)

The script proposes the following options, depending on the certificate:

• ECDSA:
  • TLS-ECDHE-ECDSA-WITH-AES-128-GCM-SHA256
  • TLS-ECDHE-ECDSA-WITH-AES-256-GCM-SHA384
• RSA:
  • TLS-ECDHE-RSA-WITH-AES-128-GCM-SHA256
  • TLS-ECDHE-RSA-WITH-AES-256-GCM-SHA384

It defaults to TLS-ECDHE-*-WITH-AES-128-GCM-SHA256.

Diffie-Hellman key exchange

OpenVPN uses a 2048 bits DH key by default.

OpenVPN 2.4 added support for ECDH keys. Elliptic curve cryptography is faster, lighter and more secure.

Also, generating a classic DH keys can take a long, looong time. ECDH keys are ephemeral: they are generated on-the-fly.

The script provides the following options:

• ECDH: prime256v1/secp384r1/secp521r1 curves
• DH: 2048/3072/4096 bits keys

It defaults to prime256v1.

HMAC digest algorithm

From the OpenVPN wiki, about --auth:

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.

SHA1 isn't safe anymore.

The script provides the following choices:

• SHA256
• SHA384
• SHA512

It defaults to SHA256.

tls-auth and tls-crypt

From the OpenVPN wiki, about 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.

About tls-crypt:

Encrypt and authenticate all control channel packets with the key from keyfile. (See --tls-auth for more background.)

Encrypting (and authenticating) control channel packets:

• provides more privacy by hiding the certificate used for the TLS connection,
• makes it harder to identify OpenVPN traffic as such,
• provides "poor-man's" post-quantum security, against attackers who will never know the pre-shared key (i.e. no forward secrecy).

So both provide an additional layer of security and mitigate DoS attacks. They aren't used by default by OpenVPN.

tls-crypt is an OpenVPN 2.4 feature that provides encryption in addition to authentication (unlike tls-auth). It is more privacy-friendly.

The script supports both and uses tls-crypt by default.

Say thanks

You can say thanks if you want!

Credits & Licence

Many thanks to the contributors and Nyr's orginal work.

This project is under the MIT Licence