weasel-pageant

weasel-pageant allows you to use SSH keys held by PuTTY's Pageant "daemon" (or compatible, such as the version of Pageant included in PuTTY-CAC or the SSH agent mode in Gpg4win) from inside the Windows Subsystem for Linux.

The source (and this documentation) is heavily based on ssh-pageant 1.4 by Josh Stone, which allows interacting with Pageant from Cygwin/MSYS programs.

weasel-pageant works like ssh-agent, except that it leaves the key storage to PuTTY's Pageant. It sets up an authentication socket and prints the environment variables, which allows the OpenSSH client to use it. It works by executing from the WSL side a Win32 helper program which interfaces with Pageant and communicating with it through pipes.

It is probably the most useful if your SSH keys can't be copied to the WSL environment, such as when using a smart card for SSH authentication. Both Pageant-CAC and Gpg4win have been tested (note that when using Gpg4win, only the SSH authentication functionality will be forwarded; the Windows-side gpg-agent will not be available on the WSL side).

SECURITY NOTICE: All the usual security caveats applicable to WSL apply here too. Most importantly, all interaction with the Win32 world happens 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 can access the SSH keys stored in your Pageant with weasel-pageant. This is a fundamental part of how WSL works; 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: weasel-pageant does not, and will never work on a version of Windows 10 older than 1703 ("Creators Update"), because it requires the new Windows/Ubuntu interoperability support feature shipped with version 1703. It has been verified to work with versions up to and including 1709 ("Fall Creators Update", build 16299.64).

Non-Ubuntu distributions (available since 1709) have not been tested, but they should work as well. Please open a GitHub issue if something is broken.

If you are still using Anniversary Update, you may be able to use the (unrelated) wsl-ssh-pageant.

Installation

From binaries

Download the zip file from the releases page and unpack it in a convenient location on the Windows part of your drive. Because WSL can only execute Win32 binaries from drvfs locations, weasel-pageant will not work if unpacked inside the WSL filesystem (onto an lxfs mount). (Advanced users may place only helper.exe on drvfs, but in general it is easier to keep the pieces together.)

From source

A VS2017 project is included. You will need the "Desktop development with C++" and "Linux development with C++" features.

1. In VS2017, set up a connection to your WSL environment (or a remote Linux machine) in Options → Cross Platform → Connection Manager.

2. Optional: If you intend to work on the Linux sources, copy the contents of /usr/include into linux/include under the project directory. This is not required for the build, but will make Intellisense more useful.

3. Hit Build Solution and both the Linux executable and the Win32 helper will be built.

If you want to create a binary package, you can use the create_pkg.py script at the root of the project. This should work with Python 3.4 or newer on either Windows or Linux.

Alternatively you can build the Linux executable directly on Linux and only use Visual Studio for the Win32 helper (no Makefile or similar is supplied at the moment). In theory the helper should be buildable with MinGW-w64 for a fully Linux-based build, but this has not been tested.

The release binaries have been built with VS2017 15.3.0 Preview 2.0.

Usage

Using weasel-pageant is generally similar to using ssh-agent on Linux and similar operating systems.

1. Ensure that PuTTY's Pageant is running (and holds your SSH keys).

   • weasel-pageant does not start Pageant itself.
   • Recommended: Add Pageant to your Windows startup/Autostart configuration so it is always available.

2. Edit your ~/.bashrc (or ~/.bash_profile) to add the following:

    eval $(<location where you unpacked the zip>/weasel-pageant -r -a "/tmp/.weasel-pageant-$USER")
   

   To explain:

   • This leverages the -r/--reuse option in combination with -a SOCKET, which will only start a new daemon if the specified path does not accept connections already. If the socket appears to be active, it will just set SSH_AUTH_SOCK and exit.

   • The exact path used for -a is arbitrary. The socket will be created with only user-accessible permissions, but you may still want to use a more private path than shown above if multiple users can access your WSL instance.

   • When using this, the weasel-pageant daemon and its helper process helper.exe remains active (both will be visible in the Windows task manager). You should not kill these processes, since open shells might still be using the socket.

   • Using eval will set the environment variables in the current shell. By default, weasel-pageant tries to detect the current shell and output appropriate commands. If detection fails, then use the -S SHELL option to define a shell type manually.

3. Restart your shell or type (when using bash) . ~/.bashrc. Typing ssh-add -l should now list the keys you have registered in Pageant.

Options

weasel-pageant aims to be compatible with ssh-agent options, with a few extras:

$ weasel-pageant -h
Usage: weasel-pageant [options] [command [arg ...]]
Options:
  -h, --help     Show this help.
  -v, --version  Display version information.
  -c             Generate C-shell commands on stdout.
  -s             Generate Bourne shell commands on stdout.
  -S SHELL       Generate shell command for "bourne", "csh", or "fish".
  -k             Kill the current weasel-pageant.
  -d             Enable debug mode.
  -q             Enable quiet mode.
  -a SOCKET      Create socket on a specific path.
  -r, --reuse    Allow to reuse an existing -a SOCKET.
  -H, --helper   Path to the Win32 helper binary (default: /mnt/c/Program Files/weasel-pageant/helper.exe).
  -t TIME        Limit key lifetime in seconds (not supported by Pageant).

By default, the Win32 helper will be searched for in the same directory where weasel-pageant is stored. If you have placed it elsewhere, the -H flag can be used to set the location.

Known issues

• The Win32 helper cannot be restarted if it's killed or crashes. There appears to be a bug in WSL that causes pipes passed to Win32 executables to be unusable after some point in program execution (possibly related to forking processes or opening sockets). Currently, weasel-pageant will exit if it detects that the helper has exited.

Uninstallation

To uninstall, just remove the extracted files and any modifications you made to your shell initialization files (i.e. .bashrc).

Version History

• 2017-06-25: 1.0 - Initial release.

Contributions

Please send bug reports using Github's issues feature. Pull requests are also welcome, though if you intend to do major changes it's recommended to open an issue first.

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Copyright 2017 Valtteri Vuorikoski

Based on ssh-pageant, copyright (C) 2009-2014 Josh Stone

Licensed under the GNU GPL version 3 or later, http://gnu.org/licenses/gpl.html

This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

See the COPYING file for license details.
Part of weasel-pageant is derived from the PuTTY program, whose original license is in the file COPYING.PuTTY.