**NOTE:** OpenVPN's drivers (tap-windows6 mainly) was in the process of getting the WHQL certification years ago. Then we realized that Microsoft documentation is wrong and WHQL certification is **not** necessary for the drivers on Windows Server platforms. Due to complexities in getting HLK tests to pass, which is/was a requirement for WHQL certification, we basically just gave up. This article is retained because it may help somebody else on a more general level.
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Microsoft has some documentation about HLK testing and WHQL signing, but it is quite incomplete, and there is lots of room for speculation and anecdotes. Practical testing is often required to understand the requirements fully. Therefore some of the requirements documented in this article are bound to change.
Different Windows versions have different kernel-mode signing options:
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# HLK test environment overview
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HLK testing always requires a HLK !Controller/Studio node, plus one or more HLK clients. The HLK client Windows version and HLK versions need to be in sync [as described in MS documentation](https://docs.microsoft.com/en-us/windows-hardware/test/hlk/). For example, if your goal is to get a signature for Windows Server 2019 you need to use HLK 1809. This requirement is clearly outlined in the [HLK 1809 release blog post](https://techcommunity.microsoft.com/t5/Windows-Hardware-Certification/Accepting-Windows-10-version-1809-and-Windows-Server-2019/ba-p/364926). Additionally since [HLK 1709 release](https://techcommunity.microsoft.com/t5/Windows-Hardware-Certification/Accepting-Windows-10-version-1803-submissions/ba-p/364921) HLK will support testing a single Windows 10 version only.
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HLK testing always requires a HLK Controller/Studio node, plus one or more HLK clients. The HLK client Windows version and HLK versions need to be in sync [as described in MS documentation](https://docs.microsoft.com/en-us/windows-hardware/test/hlk/). For example, if your goal is to get a signature for Windows Server 2019 you need to use HLK 1809. This requirement is clearly outlined in the [HLK 1809 release blog post](https://techcommunity.microsoft.com/t5/Windows-Hardware-Certification/Accepting-Windows-10-version-1809-and-Windows-Server-2019/ba-p/364926). Additionally since [HLK 1709 release](https://techcommunity.microsoft.com/t5/Windows-Hardware-Certification/Accepting-Windows-10-version-1803-submissions/ba-p/364921) HLK will support testing a single Windows 10 version only.
According to practical testing done by [wintun](https://www.wintun.net/) developers it is possible to get a code signature that is valid for all Windows 10 platforms using the following HLK clients:
