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, 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
• Windows Driver Kit for Windows 10

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 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, open \\.\Device\WINTUN%d as Local System, where %d is the LUID index (NetLuidIndex member) of the network device. You may then ReadFile and 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 for this. If using blocking I/O instead, it may be desirable to open separate handles for reading and writing.