wintun/README.md

# Wintun Network Adapter
### TUN Device Driver for Windows

This is a layer 3 TUN driver for Windows 7, 8, 8.1, and 10. Originally created for [WireGuard](https://www.wireguard.com/), it is intended to be useful to a wide variety of projects that require layer 3 tunneling devices with implementations primarily in userspace.

## Build Requirements

- [Visual Studio 2017](https://visualstudio.microsoft.com/downloads/)
- [Windows Driver Kit for Windows 10](https://docs.microsoft.com/en-us/windows-hardware/drivers/download-the-wdk)


## Digital Signing

Digital signing is integral part of the build process. By default, the driver will be test-signed using a certificate that the WDK should automatically generate. To subsequently load the driver, you will need to put your computer into test mode by executing as Administrator `bcdedit /set testsigning on`.

If you possess an EV certificate for kernel mode code signing you should switch TUN driver digital signing from test-signing to production-signing by authoring your `wintun.vcxproj.user` file to look something like this:

```xml
<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <SignMode>ProductionSign</SignMode>
    <CrossCertificateFile>$(WDKContentRoot)CrossCertificates\DigiCert_High_Assurance_EV_Root_CA.crt</CrossCertificateFile>
    <ProductionCertificate>CN=WireGuard LLC, O=WireGuard LLC, L=Boulder, S=Colorado, C=US, SERIALNUMBER=4227913, OID.2.5.4.15=Private Organization, OID.1.3.6.1.4.1.311.60.2.1.2=Ohio, OID.1.3.6.1.4.1.311.60.2.1.3=US | DF98E075A012ED8C86FBCF14854B8F9555CB3D45</ProductionCertificate>
  </PropertyGroup>
</Project>
```

Modify the `<CrossCertificateFile>` to contain the full path to the cross-signing certificate of CA that issued your certificate. You should be able to find its `.crt` file in `C:\Program Files (x86)\Windows Kits\10\CrossCertificates`. Note that the `$(WDKContentRoot)` expands to `C:\Program Files (x86)\Windows Kits\10\`.

If you already have `wintun.vcxproj.user` file, just add the `<PropertyGroup>` section.

## Usage

After loading the driver and creating a network interface the typical way using [SetupAPI](https://docs.microsoft.com/en-us/windows-hardware/drivers/install/setupapi), open `\\.\Device\WINTUN%d` as Local System, where `%d` is the [LUID](https://docs.microsoft.com/en-us/windows/desktop/api/ifdef/ns-ifdef-_net_luid_lh) index (`NetLuidIndex` member) of the network device. You may then [`ReadFile`](https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-readfile) and [`WriteFile`](https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-writefile) bundles of packets of the following format:

```
+------------------------------+
| size_0                       |
|   4 bytes, native endian     |
+------------------------------+
|                              |
| padding                      |
|   12 bytes, all zero         |
|                              |
+------------------------------+
|                              |
| packet_0                     |
|   size_0 bytes               |
|                              |
~                              ~
|                              |
+------------------------------+
| padding                      |
|   16-((4+size_0)&15) bytes,  |
|   all zero                   |
+------------------------------+
| size_1                       |
|   4 bytes, native endian     |
+------------------------------+
|                              |
| padding                      |
|   12 bytes, all zero         |
|                              |
+------------------------------+
|                              |
| packet_1                     |
|   size_1 bytes               |
|                              |
~                              ~
```

Each packet segment should contain a layer 3 IPv4 or IPv6 packet. Up to 256 packets may be read or written during each call to `ReadFile` or `WriteFile`.

It is advisable to use [overlapped I/O](https://docs.microsoft.com/en-us/windows/desktop/sync/synchronization-and-overlapped-input-and-output) for this. If using blocking I/O instead, it may be desirable to open separate handles for reading and writing.