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 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:
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.
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:
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.
