win-gpg-agent

DEPRECATION NOTE - September 2022

I am stopping development of this project as it is inherently unsecure and very difficult to properly support. Both because it is relying on GnuPG set of tools (you could find links to critique below if interested) and because the project itself in order to provide interoperability across different Windows sub-platforms implements unsafe solutions. Nobody should be forced to deal with such a complexity in everyday work. It became obvious to me that common practices recommend somewhat simpler solutions based on OpenSSH and its extensions and since GitHub now allows code signing using OpenSSH certificates - the whole reason for this monstrosity to exists is no more. In addition, there are a number of new open source products like age and minisign which are much simpler, could be argued about and have secure defaults. And since I am no longer using gpg-agent in my day to day - I am not planning for this project to follow further GnuPG development.

Simple set of tools to make working with GPG and SSH keys easier on Windows 10/11.

Recent Windows has ssh-agent service (with support for persistence and Windows security) and I have been using it successfully for a while. However there is another set of tools entirely - GnuPG. It implements ssh-agent functionality (with somewhat more flexibility than original), supports smart cards, attempts to handle identity aspects of security and sometimes must be used (for example to sign git commits on some projects - this is an excellent explanation of code integrity aspect). All of that works reasonably well on Linux practically out of the box.

Windows usage is a bit more problematic as we have to deal with various non-cooperating pieces: GnuPG win32 binaries are somewhat deficient, OpenSSH port integrated into Windows (console, terminal and all), Cygwin/MSYS2 ssh tools and WSL1 and WSL2 add challenges with specific binaries and different lifetime management requirements. Ideally we need to have Windows host to handle single set of secured keys (SSH and GPG) while transparently providing necessary interfaces to all other environments. This project aims to create simple set of tools to be combined with GnuPG binaries for Windows to do exactly that.

DISCLAIMER When using term GnuPG I am not referring to GPG4Win, but rather to basic GnuPG tools built from code base common for all platforms. GPG4Win includes this set (which could be extracted), but normally it is available from GnuPG ftp site ftp.gnupg.org. It could be easily installed by using scoop command scoop install gnupg, chocolatey command choco install gnupg or winget command winget install GnuPG. So no wonderful KDE GUIs ported to Windows.

I am still learning the full scope of damage one could cause by using GnuPG tools and I am certainly no expert here.

If you are interested in basic guides on how to handle keys using GnuPG tools - web is full of them and this project has nothing to do with it. This one is very good (albeit somewhat outdated). You could (and probably should) read set of excellent posts by Simon Josefsson: blog_1 blog_2 blog_3. To put things in perspective and select more practical place for PGP tools overall I strongly suggest studying this critique. It resonates a lot, especially after spending some time reading GnuPG code.

NOTE Eventually many pieces of functionality from this project will become obsolete. I am sure that gpg-agent on Windows will directly support Windows OpenSSH server - T3883. Microsoft developers will finally decide how they want to handle security on Unix domain sockets and will change OpenSSH port and many other wonderful things will happen. Until then we need to create specific translation layers to compensate for deficiencies. Assuan S.gpg-agent.ssh support in GnuPG code is presently broken under Windows (at least in GnuPG 2.2.25), so we have to resort to putty/pageant method instead (which today does not work in 64 bits GnuPG builds). And WSL2 requires additional layer of translation (with socat on Linux side and either HYPER-V integration service or helper on Windows end) since AF_UNIX interop is not (yet? ever?) implemented for WSL2.

SECURITY NOTICE: All the usual security caveats applicable to WSL, SSH and GPG apply here. For example all interaction with the Win32 world happen with the credentials of the user who started the WSL environment. In practice, if you allow someone else to log in to your WSL environment remotely, they may be able to access the SSH keys stored in your gpg-agent. This is a fundamental feature of WSL; if you are not sure of what you're doing, do not allow remote access to your WSL environment (i.e. by starting an SSH server).

COMPATIBILITY NOTICE: tools from this project were tested on Windows 10 and Windows 11 with multiple distributions and should work on anything starting with build 1809 - beginning with insider build 17063 and would not work on older versions of Windows 10, because it requires AF_UNIX socket support feature. I started testing everything with "official" GnuPG LTS Windows build 2.2.27.

BREAKING CHANGES:

v1.4.0 changes default configuration values to support installation of 2.3+ GnuPG in non-portable mode. This required changing default gui.homedir and introducing gpg.socketdir to avoid gpg-agent sockets being overwritten by agent-gui due to name conflict. This change may require adjusting your configuration and usage scripts.

Installation

Installing using Scoop

    scoop bucket add extras
    scoop install win-gpg-agent

Updating

    scoop update win-gpg-agent

Installing manually

Download archive from the releases page and unpack it in a convenient location. For example:

using PowerShell

	Push-Location -Path $env:USERPROFILE  # Or, wherever you want the win-gpg-agent directory located 
	$uriLatestWinGpgAgentZip = Invoke-RestMethod -Uri "https://api.github.com/repos/rupor-github/win-gpg-agent/releases/latest"  | Select-Object -Property assets -ExpandProperty assets |  Where-Object -FilterScript {$_.name -eq "win-gpg-agent.zip" } | Select-Object -Property browser_download_url -ExpandProperty browser_download_url 
	Invoke-WebRequest  -OutFile "win-gpg-agent.zip" -Uri $uriLatestWinGpgAgentZip
	Expand-Archive .\win-gpg-agent.zip
	Remove-Item .\win-gpg-agent.zip
	Pop-Location

NOTE Starting with v1.2.2 releases are packed with zip and signed with minisign. Here is public key for verification:

RWTNh1aN8DrXq26YRmWO3bPBx4m8jBATGXt4Z96DF4OVSzdCBmoAU+Vq

Usage

Make sure GnuPG works. Create/import keys, setup smart cards, etc. NOTE that WSL1/WSL2 distribution use case (while seems local and Windows native) does not mean that you should directly share gpg databases from Windows end even if you technically could. For all means and purposes those are "remote" cases - the only difference I could think of is usage of S.gpg-agent socket rather than more restricted S.gpg-agent.extra socket. Multiple WSL1 instances could probably share database and multiple WSL2 instances could probably share databases, but in general each distro should have its own. If you need more details - read gpg man pages. To put it simply: you still need to export public keys on Windows end and import them on remote end, even if this means simply using

    gpg --export --armor [email protected] ...
    gpg --import ...

If you are using Windows native ssh-agent - stop it. You may want to delete all keys from its vault - you will need those keys in gpg vault instead.

    Stop-Service ssh-agent
    Set-Service -StartupType Disabled ssh-agent

If you would like to use Cygwin/MSYS2 ssh tools (as is the case by default with Git4Windows) you may want to consider placing gui.openssh: cygwin in agent-gui config file. Or you may add following line to your home directory .bashrc:

    export SSH_AUTH_SOCK=$(cygpath ${WSL_AGENT_HOME})/S.gpg-agent.ssh.cyg

Or you may consider switching it to win32-openssh (installed as a Windows feature or more recent version via scoop) by setting GIT_SSH environment variable on Windows side:

    $Env:GIT_SSH="$(scoop prefix win32-openssh)/ssh.exe"

NOTE that in any case you need to manage SSH_AUTH_SOCK environment variable value on on either side per environment. It has to point to named pipe for Windows OpenSSH to work and to Cygwin socket file for Cygwin/MSYS2 tools and both sets are using the same variable name.

Run agent-gui.exe

Here is a diagram to show simplified relationship between parts:

Unfortunately due to environment complexity it is difficult to provide simple step-by-step guide. I will try to explain what each piece does (as they could be used separately from each other) and then provide an example setup.

There are presently 3 executables included in the set: agent-gui.exe, pinentry.exe and sorelay.exe

agent-gui.exe

GUI wrapper for gpg-agent

Version:
	1.0.0 (go1.15.6)

Usage: agent-gui.exe [-dh] [-c path]
 -c, --config=path  Configuration file [agent-gui.conf]
 -d, --debug        Turn on debugging
 -h, --help         Show help

Is is a simple "notification tray" applet which does gpg-agent.exe lifetime management. When started it will

attempt to locate GnuPG installation and start gpg-agent with "proper" command line parameters.
make sure that gpg-agent will use pinentry.exe from the same directory where agent-gui.exe is.
make sure that it functions by communicating with it.
create AF_UNIX socket counterparts for Assuan sockets from gpg-agent (except "browser" and "ssh" ones) and handle translation. I have no use for "browser" and S.gpg-agent.ssh presently does not work on Windows.
create and service named pipe for Windows native OpenSSH. NOTE OpenSSH (native and Cygwin) and AF_UNIX socket and named pipe are using pageant protocol to talk to gpg-agent.
create and service Cygwin socket for Cygwin/MSYS2 build of OpenSSH. NOTE OpenSSH (native and Cygwin) and AF_UNIX socket and named pipe are using pageant protocol to talk to gpg-agent.
Prepare TCP socket to service XAgent protocol and make it properly discoverable by XShell (create necessary windows etc). NOTE Socket will be using pageant protocol to talk to gpg-agent.
create and service tcp socket on "localhost:extra_port" for Win32-OpenSSH redirection (it does not presently supports unix socket redirection). This requres configuration and is disabled out of the box.
set environment variable SSH_AUTH_SOCK on Windows side to point either to pipe name so native OpenSSH tools know where to go or to Cygwin socket file to be used with Cygwin/MSYS2 ssh binaries.
create WIN_GNUPG_HOME, WSL_GNUPG_HOME, WIN_GNUPG_SOCKETS, WSL_GNUPG_SOCKETS, WIN_AGENT_HOME, WSL_AGENT_HOME environment variables, setting them to point to directories with Assuan sockets and AF_UNIX sockets and register those environment variables with WSLENV for path translation. Basically WSL_* would be paths on the Linux side and WIN_* are Windows ones. This way every WSL environment started after will have proper "unix" and "windows" paths available for easy scripting.
serve as a backend for gclpr remote clipboard tool. NOTE Starting with v1.1.0 gclpr server backend enforces protocol versioning and may require upgrade of gclpr.

You could always see what is going on by clicking "Status" on applet's menu:

Reasonable defaults are provided (but could be changed by using configuration file). Full path to configuration file could be provided on command line. If not program will look for agent-gui.conf in the same directory where executable is. It is YAML file with following defaults:

gpg:
  install_path: "${ProgramFiles(x86)}\\gnupg"
  homedir: "${APPDATA}\\gnupg"
  socketdir: "${LOCALAPPDATA}\\gnupg"
gui:
  debug: false
  setenv: true
  openssh: native
  ignore_session_lock: false
  deadline: 1m
  xagent_cookie_size: 16
  pipe_name: "\\\\.\\pipe\\openssh-ssh-agent"
  homedir: "${LOCALAPPDATA}\\gnupg\\agent-gui"
  gclpr:
    port: 2850

Full list of configuration keys:

gpg.install_path - installation directory of GnuPG suite
gpg.homedir - will be supplied to gpg-agent on start as --homedir
gpg.socketdir - gnupg 2.3+ (T5537) being installed in non-portable mode creates sockets in directory, different from homedir. To be exact default home directory continues to be ${APPDATA}\gnupg, but sockets are now created in ${LOCALAPPDATA}\gnupg. Changing gpg.homedir to ${LOCALAPPDATA}\gnupg does not help - gnupg will use subdirectory of ${LOCALAPPDATA}\gnupg deriving name of sha1 hash with "d." prepended to it. This configuration allows to compensate this - if set it will be used by win-gpg-agent to locate sockets created by gpg-agent proper while keeping home directory unchanged. Make sure that gpg.socketdir and gui.homedir are not pointing to the same location or socket names for gpg-agent and agent-gui will overlap causing havoc. If explicitly set to empty string gpg.homedir value will be used instead
gpg.use_standard_pinentry - if absent or set to false (default) pinentry supplied with win-gpg-agent will be used no matter what is specified in gnupg gpg-agent configuration. If set to true win-gpg-agent would not force command line overwrite allowing you to use gpg-agent.conf instead.
gpg.gpg_agent_conf - if defined will be supplied to gpg-agent on start
gpg.gpg_agent_args - array of additional arguments to be passed to gpg-agent on start. No checking is performed
gui.debug - turn on debug logging. Uses OutputDebugStringW - use Sysinternals debugview to see
gui.setenv - automatically prepare environment variables
gui.openssh - when value is cygwin set environment SSH_AUTH_SOCK on Windows side to point to Cygwin socket file rather then named pipe, so Cygwin and MSYS2 ssh build could be used by default instead of what comes with Windows.
gui.extra_port - Win32-OpenSSH does not know how to redirect unix sockets yet, so if you want to use windows native ssh to remote "S.gpg-agent.extra" specify some non-zero port here. Program will open this port on localhost and you can use socat on the other side to recreate domain socket. By default it is disabled
gui.xagent_cookie_size - Size of the cookie used to perform XAgent protocol handshake. If set to 0 XAgent server would not be started at all. See XShell for details.
gui.ignore_session_lock - continue to serve requests even if user session is locked
gui.pipe_name - full name of pipe for Windows OpenSSH
gui.homedir - directory to be used by agent-gui to create sockets in
gui.deadline - since code which does translation from Assuan socket to AF_UNIX socket has no understanding of underlying protocol it could leave servicing go-routine handing forever (ex: client process died). This value specifies inactivity deadline after which connection will be collected
gui.gclpr.port - server port for gclpr backend
gui.gclpr.line_endings - line ending translation for gclpr backend
gui.gclpr.public_keys - array of known public keys for gclpr backend

pinentry.exe

Pinentry program for GnuPG

        1.0.0 (go1.15.6)

Usage: pinentry.exe [-dh] [-c path] [--version]
 -c, --config=path  Configuration file [C:\Users\mike0\.wsl\pinentry.conf]
 -d, --debug        Turn on debugging
 -h, --help         Show help
     --version      Show version information

It is pretty mundane pinentry implementation, I tried to follow everything I could find from GnuPG documentation and pinentry code. Since it is using WIndows Credentials API to show GETPIN dialogs a lot of "visuals" from pinentry protocol are either useless or cannot be easily implemented (timeouts, display settings etc).

I think it could be used as pinentry replacement on Windows even without agent-gui (for example to be called from WSL gpg if you decide to keep your vault there and ignore WIndows GnuPG completely) to show proper GUI dialogs:

If you let it - it will save passwords in Windows Credential Manager as "Generic Credentials" providing decent level of convenience and integration:

NOTE Starting with 1.6.0 "Remember me" check box will initially be unchecked (previously it was always checked) and pinentry will use its last used state next time.

Configuration file is almost never needed, but just in case full path to configuration file could be provided on command line. If not program will look for pinentry.conf in the same directory where executable is. It is YAML file with following defaults:

gui:
  debug: false
  pin_dialog:
    delay: 300ms
    name: Windows Security
    class: Credential Dialog Xaml Host

gui.debug - turn on debug logging. Uses OutputDebugStringW - use Sysinternals debugview to see
gui.pindialog.* - since gpg-agent starts pinentry which in turn calls Windows APIs to show various dialogs often due to the timing resulting dialog could be left in the background. Those parameters specify artificial delay and name/class for window to be attempted to be brought into foreground forcefully.

sorelay.exe

Socket relay program for WSL

        1.0.0 (go1.15.6)

Usage: sorelay.exe [-adh] [-c path] [--version] path-to-socket
 -a, --assuan       Open Assuan socket instead of Unix one
 -c, --config=path  Configuration file [C:\Users\mike0\.wsl\sorelay.conf]
 -d, --debug        Turn on debugging
 -h, --help         Show help
     --version      Show version information

This is helper program along the lines of John Starks' npiperelay.exe. Put it somewhere on devfs for interop to work its magic and combine with socat on WSL2 side and you could easily convert both Windows Assuan and Windows AF_UNIX sockets into sockets on WSL2 Linux end.

As an example (use your path and proper escaping) following will translate Windows side Assuan socket:

( setsid socat UNIX-LISTEN:/home/rupor/.gnupg/S.gpg-agent,fork EXEC:"${HOME}/winhome/.wsl/sorelay.exe -a c\:/Users/mike0/AppData/Local/gnupg/S.gpg-agent",nofork & ) >/dev/null 2>&1

And this (use your path and proper escaping) will translate Windows side AF_UNIX socket:

( setsid socat UNIX-LISTEN:/home/rupor/.gnupg/S.gpg-agent,fork EXEC:"${HOME}/winhome/.wsl/sorelay.exe c\:/Users/mike0/AppData/Local/gnupg/S.gpg-agent",nofork & ) >/dev/null 2>&1

You really have to be on WSL2 in order for this to work - if you see errors like Cannot open netlink socket: Protocol not supported - you probably are under WSL1 and should just use AF_UNIX sockets directly. Run wsl.exe -l --all -v to check what is going on. When on WSL2 make sure that socat is installed and sorelay.exe is on windows partition and path is right.

Configuration file is never needed, but just in case full path to configuration file could be provided on command line. If not program will look for sorelay.conf in the same directory where executable is. It is YAML file with following defaults:

gui:
  debug: false

Troubleshooting

In most cases all what's required is a simple agent-gui.conf adgustment, however sometimes with non typical installations you may need to dig diper and try to understand what is going on both in agent-gui and in underlying gpg-agent. Here are couple of pointers:

In many cases to see what is going on you just have to look at ssh debug trace, something like ssh -vvv host.
All agent-gui components have debug switch to activate additional logging. Internally logging is using Win32 OutputDebugString API call - so you would need to use debugger or tool like Sysinternals DebugView to see and capture it.
When this is not enough you may want to turn on debug logging in GnuPG tools, it is pretty well documented but just in case: I have scoop based portable GmuPG installation (gpgconf.ctl is present in bin subdirectory of installation). In order to see full trace of gpg-agent I create ${APPDATA}\gnupg\gpg-agent.conf (exact location depends on your installation) with following content:

debug-all
debug-level guru
log-file "local/path/to/the/log/file"
verbose
verbose
verbose

Before creating issues and asking for help, please, see if you could diagnose what is going on - you'd need to do this anyways and this will save everybody a lot of time. Remember - win-gpg-agent tools are making GnuPG integration with various variants of WIndows environments easier, but they would not provide any functionality GnuPG tools do not provide. So always make sure that what you want is actually supported by original GnuPG set.

Example

Putting it all together nicely - remote here refers to your wsl shell or some other box or virtual machine you could ssh to. Goal here is to have a setup which could be used the same way in different Linux instance with minimal changes and customization - be it native Linux install, something I ssh into or WSL distro running. We should be able to use a small set of safely stored private keys and be able to forward both gpg and ssh everywhere with minimal complexity (at least it should be manageable).

For my WSL installations I always create ~/winhome and link it to my Windows home directory (where I have .wsl directory with various interoperability tools from Windows side). I am assuming that gclpr is in your path on remote and you installed it's Windows counterpart somewhere in drvfs location (~/winhome/.wsl is a good place).

I auto-start agent-gui.exe on logon on my Windows box - no special customization is needed (except for gclpr public keys from various locations I would like to share my clipboard with)

I am using scoop for GnuPG and win-gpg-agent installations which results in portable GnuPG mode. With gnupg 2.3.3 release gpg.socketdir is not required and must be set to empty string in config file. With gnupg 2.3.4 configuration must be changed yet again. Look for up to date comments in scoop installation manifest win-gpg-agent.json or agent-gui.conf after installation. In your scripts you may need to use WIN_GNUPG_HOME or WIN_GNUPG_SOCKETS environment variables to properly setup socket paths as they change from version to version. Please pay attention, code below is an example and may need modification.

In my .bashrc I detect what I have and where it runs using code like this:

    # detect what we have
    if uname -a | grep -q Microsoft; then
        # WSL 1 could use AF_UNIX sockets from Windows side directly
        if [ "${WSL_AGENT_HOME}" ]; then
            export GNUPGHOME=${WSL_AGENT_HOME}
            export SSH_AUTH_SOCK=${WSL_AGENT_HOME}/S.gpg-agent.ssh
        fi
    elif uname -a | grep -q microsoft; then
        # WSL 2 needs help from socat/sorelay
        ${HOME}/.local/bin/win-gpg-agent-relay start
        export SSH_AUTH_SOCK=${HOME}/.gnupg/S.gpg-agent.ssh
    else
        # Do whatever -- this is real Linux
    fi

Where win-gpg-agent-relay is heavily based on the work of others NOTE It is for Debian based distros only!

My .ssh/config entries used to ssh to remote have port forwarding enabled for gclpr:

RemoteForward 2850 127.0.0.1:2850

On remote my tmux.conf includes following lines:

# --- clipboard -------------------------------------------------------------------
set -g set-clipboard off
if-shell 'if [ -n ${WSL_DISTRO_NAME} ]; then true; else false; fi' \
  'bind-key -T copy-mode-vi Enter send-keys -X copy-pipe-and-cancel "~/winhome/.wsl/gclpr.exe copy" ; bind-key -T copy-mode-vi MouseDragEnd1Pane send-keys -X copy-pipe-and-cancel "~/winhome/.wsl/gclpr.exe copy"' \
  'bind-key -T copy-mode-vi Enter send-keys -X copy-pipe-and-cancel "gclpr copy" ; bind-key -T copy-mode-vi MouseDragEnd1Pane send-keys -X copy-pipe-and-cancel "gclpr copy"'

And my neovim configuration file init.vim on remote has following lines:

set clipboard+=unnamedplus
if has("unix")
	" ----- on UNIX ask lemonade to translate line-endings
	if empty($WSL_DISTRO_NAME)
		if executable('gclpr')
			let g:clipboard = {
				\   'name': 'gclpr',
				\   'copy': {
				\      '+': 'gclpr copy',
				\      '*': 'gclpr copy',
				\    },
				\   'paste': {
				\      '+': 'gclpr paste --line-ending lf',
				\      '*': 'gclpr paste --line-ending lf',
				\   },
				\   'cache_enabled': 0,
				\ }
		endif
	else
		" ---- we are inside WSL - reach out to the Windows side
		if executable($HOME . '/winhome/.wsl/gclpr.exe')
			let g:clipboard = {
				\   'name': 'gclpr',
				\   'copy': {
				\      '+': $HOME . '/winhome/.wsl/gclpr.exe copy',
				\      '*': $HOME . '/winhome/.wsl/gclpr.exe copy',
				\    },
				\   'paste': {
				\      '+': $HOME . '/winhome/.wsl/gclpr.exe paste --line-ending lf',
				\      '*': $HOME . '/winhome/.wsl/gclpr.exe paste --line-ending lf',
				\   },
				\   'cache_enabled': 0,
				\ }
		endif
	endif
endif

Using SSH and Linux you could remote GnuPG extra socket as far as you want by adding something like this to you .ssh/config where you want it:

RemoteForward /home/rupor/.gnupg/S.gpg-agent /home/rupor/.gnupg/S.gpg-agent.extra

In case you prefer to use Win32-OpenSSH you will need to set gui.extra_port in configuration and RemoteForward it, using something like

socat UNIX-LISTEN:/run/user/1000/gnupg/S.gpg-agent,fork TCP4-CONNECT:127.0.0.1:$extra_port

on remote to recreate domain socket.

Just follow this guide - it will allow you to sign you git commits everywhere using single private key while keeping it in a single safe place (like smart card). You will still have to distribute and import public key in multiple places, which may be inconvenient but should be secure. You could read a bit more on that.

Credits

Thanks to Ben Pye with his wsl-ssh-pageant for inspiration.
Thanks to Masataka Pocke Kuwabara for lemonade - a remote utility tool. (copy, paste and open browser) over TCP.
Thanks to John Starks for npiperelay - access to Windows pipes from WSL.
Thanks to Max Mazurov for go-assuan
Thanks to Daniel Joos for wincred

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