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https://github.com/roburio/openvpn

An opinionated implementation of the OpenVPN protocol
https://github.com/roburio/openvpn

mirageos ocaml openvpn openvpn-client openvpn-server unikernel vpn

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An opinionated implementation of the OpenVPN protocol

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README 

        
## MirageVPN library purely in OCaml



MirageVPN creates secure point-to-point or site-to-site connections in routed or bridged configurations and remote access facilities.

It uses TLS to establish a (mutually) authenticated connection, over which material to derive the symmetric keys for packet encryption is exchanged.

The protocol is compatible with OpenVPN™.



The goal of this project is to provide:

- A pure library implementing the protocol logic, and the OpenVPN™ config file format to enable interoperabilty and a smooth transition for existing deployments.

- [MirageOS](https://mirage.io) unikernels that act as OpenVPN™-compatible client and server.



We provide a [handbook](https://robur-coop.github.io/miragevpn-handbook/) to guide you to install MirageVPN.



Our goal is not to implement the complete protocol, but rather a small useful subset with modern crypto and the latest key exchange methods, without deprecated or redundant features

(embodying the philosophy of [OCaml-tls](https://github.com/mirleft/ocaml-tls)).  An initial draft of the network setup is depicted in the diagram below:



![diagram](/diagrams/multi-stack.svg)



Since OpenVPN™ is not detailed in a protocol specificaton specified, apart from comments in the header files, we have written a [specification document](https://github.com/robur-coop/miragevpn-spec) in Markdown, still work in progress.



Our configuration parser can be tested with an OpenVPN™ configuration file:



  - `./_build/default/app/openvpn_config_parser.exe my.openvpn.conf`



# Unix client `miragevpn_client_lwt`



Included in this repository is a unix program that will connect to an

OpenVPN™ server, open a `tun` interface, and tunnel packets between

the two.



## Unix client on Linux



There are two ways to open `tun` interfaces:

1) Using a dynamically allocated interface (`dev tun`).

   In order to dynamically allocate a `tun` interface, the process will need

   privileges to do so. Either by running the client as `root` or with

   the `CAP_NET_ADMIN` privilege.

   You would then add `dev tun` to your configuration file.

2) Using a preallocated interface (`dev tunX`)

   This is the recommend configuration.

   To allocate such an interface for `tun5` you can use this command:

   ```shell

   sudo ip tuntap add mode tun user MYUSERNAME name tun5

   ```

   You would then add `dev tun5` to your configuration file.



```shell

dune build



# Bestowing the binary with CAP_NET_ADMIN if using dynamic tun allocation:

sudo setcap cap_net_admin=ep ./_build/default/app/miragevpn_client_lwt.exe



./_build/default/app/miragevpn_client_lwt.exe -v MY-CONFIG-FILE.CONF

```



# OpenVPN™-compatible config parser



Our goal has been to implement a usable subset (as found in various

 real-world configuration files available to us during the implementation

 phase).



As far as possible we have strived to derive a representation that does not

 permit ambiguity or conflicting options to be present in the parsed config.

Consult the `type 'a k` declaration in `openvpn_config.mli` for more

 information.



This does not mean that conflicting options cannot be accepted from an on-disk

 configuration file, but rather that such conflicts are explicitly handled in

 the parser code (specifically in the `resolve_conflict` function).



A notable difference from OpenVPN™ configuration parser is that we treat relative

 paths in a configuration file to be relative to the configuration file

 location, and not relative to the current working directory. OpenVPN™ supports

 a `--cd` argument, which we do not.



You can check compatibility with your configuration file by executing

```shell

dune build

./_build/default/app/openvpn_config_parser.exe MY-CONFIG-FILE.CONF

```



## Discrepancies between MirageVPN and OpenVPN™



The "verify-x509-name  name" in OpenVPN™ checks by default only the

commonName of the subject in the X.509 certificate. MirageVPN validates the

provided host against the set of hostnames in the certificate, namely the union

of the commonName and the DNS entries in the SubjectAlternativeName extension.



When using a PKCS#12 file the certificates in it are not used to authenticate

the remote. OpenVPN™ will use the certificates if (and only if) no "ca" option

is specified. If it is desired to use the certificates from the PKCS#12 file

to authenticate the remote the certificates can be added with the "ca" option

by extracting the certificates with e.g. `openssl pkcs12`.



For tls clients (as opposed to static key clients) we only support data channel

AEAD ciphers. This means the `--auth` option is ignored for data channel

authentication for tls clients. For `--tls-auth` it is still used to choose the

hmac used for the control channel while for `--tls-crypt` and `--tls-crypt-v2`

the hmac is hardcoded (as per OpenVPN™).



If a "port" is specified, "lport" and "rport" may not be specified.



If a "remote" is specified with an IP address and no protocol (and thus no

address family), and a default "proto" with an IP address family is specified,

we ignore that default IP address family:

```

proto udpv6

remote 127.0.0.1

```

We consider this as "remote 127.0.0.1  udp4".



## Funding



This project was funded in 2019 for six months by the [German federal ministry for education and research](https://www.bmbf.de) via the [Prototypefund](https://prototypefund.de) - the amount was 47500 EUR.



In 2023, we received funding from European Union in the Next Generation Internet project ([NGI assure](https://www.assure.ngi.eu/), via [NLnet](https://nlnet.nl). The scope was updating to the current protocol version (tls-crypt-v2 etc.), a QubesOS client, a server implementation, and more documentation. The amount was 57000 EUR. Learn more at the [NLnet project page](https://nlnet.nl/project/MirageVPN).