README.md

Simple-VPN

This project is a VPN-server, written in golang, using websockets as a transport. The idea is that multiple-nodes each connect to a central VPN-server, and once connected they can talk to each other securely, regardless of their location, on a private subnet.

The following image illustrates the expected setup:

• Three hosts each connect to the central VPN host.
• Once they're connected each of those hosts can then talk to the other machines which are also connected.
  • (Their private traffic is routed to the central hub, from there sent back out.)

While it is possible to use this software to mask your laptop's IP while traveling, instead showing the IP of the VPN-server as being the source of connections that is not the expected use-case. (Nor is it documented!)

It should be noted that the VPN-server will become a single point of failure if you're using it to join (say) a database-host located at Hetzner with a number of webserver-nodes split between Linode and Digital Ocean, but being a simple service, easy to deploy, it should be trivial to spin up a replacement in a hurry.

Encryption

The VPN-server does not implement any kind of encryption itself, nor does it handle access-control beyond the use of a shared-secret.

Is this insane? Actually no. I'd rather add no encryption than badly implemented encryption!

• The use of TLS prevents traffic from being sniffed.
  • This means that the connections made from one host, to another, over their private network will be unreadable to hosts in the same location.
• The use of a shared-secret prevents rogue agents from connecting to your VPN-server.
  • This means a user cannot join your private network and attempt to sniff traffic that way.

I believe this solution is "secure enough", but if you have concerns you can ensure that all the traffic you send over it uses TLS itself, for example database-connections can use TLS, etc.

Installation

Providing you have a working go-installation you should be able to install this software by running:

go get -u github.com/skx/simple-vpn

NOTE: If you've previously downloaded the code this will update your installation to the most recent available version.

Alternatively you can download the latest release from our releases page if you're running upon AMD64-GNU/Linux host. (Unfortunately we use CGO which makes compiling binaries for other platforms difficult.)

VPN-Server Setup

Configuring a VPN server requires two things:

• The simple-vpn binary to be running in server-mode..
  • This requires the use of a simple configuration-file.
• Your webserver to proxy (websocket) requests to it.
  • You must ensure that your webserver uses TLS to avoid sniffing.

A minimal configuration file for using simple-vpn in server-mode looks like this:

• etc/server.cfg

With your configuration-file you can now launch the VPN-server like so:

 # simple-vpn server ./server.cfg

To proxy traffic to this server, via nginx, you could have a configuration file like this:

server {
    server_name vpn.example.com;
    listen [::]:443  default ipv6only=off ssl;

    ssl on;
    ssl_certificate      /etc/lets.encrypt/ssl/vpn.example.com.full;
    ssl_certificate_key  /etc/lets.encrypt/ssl/vpn.example.com.key;
    ssl_dhparam /etc/nginx/ssl/dhparam.pem;

    ssl_prefer_server_ciphers on;
    ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
    ssl_ciphers 'ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:ECDHE-RSA-DES-CBC3-SHA:ECDHE-ECDSA-DES-CBC3-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA';
    add_header Strict-Transport-Security "max-age=31536000";

    proxy_buffering    off;
    proxy_buffer_size  128k;
    proxy_buffers 100  128k;

    ## VPN server ..
    location /vpn {

       proxy_set_header      X-Forwarded-For $remote_addr;
       proxy_pass            http://127.0.0.1:9000;
       proxy_http_version    1.1;
       proxy_set_header      Upgrade $http_upgrade;
       proxy_set_header      Connection "upgrade";
       proxy_read_timeout    86400;
       proxy_connect_timeout 43200000;

       tcp_nodelay on;
   }
}

• You don't need to dedicate a complete virtual host to the VPN-server, a single "location" is sufficient.
  • In this example we've chosen https://vpn.example.com/vpn to pass through to simple-vpn.

VPN-Client Setup

Install the binary upon the client hosts you wish to link, and launch them with the name of a configuration-file:

# simple-vpn client client.cfg

There is a sample client configuration file here:

• etc/client.cfg

The configuration file has two mandatory settings:

• key
  • Specifies the shared key with which to authenticate.
• vpn
  • Specifies the VPN end-point to connect to.

Advanced Configuration

The server will assign each client which connects the next unused IP address from the range it is configured to serve.

Because each client identifies itself with the hostname of the local system it is possible to map static IP addresses to any remote host, which is useful if you wish to setup DNS entries, etc.

To setup a static IP see the commented-out sections in the server.cfg file.

Steve