ENLYZE PortSniffer

An open-source driver and tool to monitor the traffic between applications and arbitrary serial or parallel ports.
Compatible with Windows XP or later (32-bit and 64-bit).

Comparison with Sysinternals Portmon

ENLYZE PortSniffer has been inspired by the Sysinternals Portmon tool, but has several distinct differences:

Advantages

Based on the modern Kernel-Mode Driver Framework (KMDF) instead of the legacy NT4 driver model, thereby correctly reacting to Plug&Play events concerning serial/parallel ports.
Compatible with 64-bit Windows versions.
The freely available source code under the permissive MIT license and a documented public interface allow easy integration into an own application.

Disadvantages

Comes with only a simple CLI application instead of a feature-rich GUI.

How to build

Install the Windows Driver Kit 7.1.0.
Open the WDK Build Environment for the minimum Windows version you want to support, your desired architecture, and the debug level. I use Windows XP x86 Free Build Environment and Windows Server 2003 x64 Free Build Environment for release versions.
Move to the root directory of your Git checkout and call build_all.

The build_on_ci.ps1 PowerShell script automates the building of release binaries with precise version information. It is currently unused, because I haven't found a public CI system with WDK 7.1.0 yet.

Goals

All bug reports and pull requests improving the driver and tool quality are very welcome!
The code has been written to follow all known best practices and coding style guidelines for Windows driver development. It currently builds with zero compiler and PREfast warnings, and shall continue to do so.

As of now, there are no plans to add a GUI. Due to the documented public interface, a GUI could very well be developed as a separate project outside the PortSniffer repository. If somebody wants to do that, this is the recommended approach, as it would also free you from the limitations of the WDK 7.1.0 Build Environment.

There are also no plans to move away from WDK 7.1.0, because the driver shall remain compatible with Windows XP.

Driver Signature

Currently, the published driver binaries are unsigned and therefore only work when disabling Driver Signature Enforcement under 64-bit Windows versions. If you don't do that, ports will fail with a Windows cannot verify the digital signature ... (Code 52) error in Device Manager after attaching the PortSniffer to them.

To temporarily disable Driver Signature Enforcement when booting Windows:

Press F8 continuously during boot to let the Advanced Boot Options screen appear. You can also directly boot into it via shutdown /r /o.
For Windows 7, you just have to choose Disable Driver Signature Enforcement and you can continue booting.
For Windows 8 or 10, click Troubleshoot -> Advanced options -> Startup Settings and press 7 to Disable driver signature enforcement.

I'm not aware of any permanent solution to disable Driver Signature Enforcement. Enabling the infamous Test Mode in the bootloader is not sufficient -- at least not for a filter driver like the PortSniffer.

Future versions of the PortSniffer binaries may come with a signature. However, Microsoft has recently been changing their driver signing policies and I'm currently not aware of a solution that works equally well for all Windows versions down to Windows 7.

Note that 32-bit operating systems are not affected by this Windows limitation. They accept unsigned drivers just fine.

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