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OpenSSH for Windows

Setup procedure for using OpenSSH client/server on Windows.

Client

# Install the OpenSSH Client
Add-WindowsCapability -Online -Name OpenSSH.Client~~~~0.0.1.0

Server

# Install the OpenSSH Server
Add-WindowsCapability -Online -Name OpenSSH.Server~~~~0.0.1.0

# Start the sshd service
Start-Service sshd

# OPTIONAL but recommended:
Set-Service -Name sshd -StartupType 'Automatic'

# Confirm the Firewall rule is configured. It should be created automatically by setup. Run the following to verify
if (!(Get-NetFirewallRule -Name "OpenSSH-Server-In-TCP" -ErrorAction SilentlyContinue | Select-Object Name, Enabled)) {
    Write-Output "Firewall Rule 'OpenSSH-Server-In-TCP' does not exist, creating it..."
    New-NetFirewallRule -Name 'OpenSSH-Server-In-TCP' -DisplayName 'OpenSSH Server (sshd)' -Enabled True -Direction Inbound -Protocol TCP -Action Allow -LocalPort 22
} else {
    Write-Output "Firewall rule 'OpenSSH-Server-In-TCP' has been created and exists."
}

Key based authentication

https://learn.microsoft.com/en-us/windows-server/administration/openssh/openssh_keymanagement

Generate key for client

  • "comment" = comment for user friendly listing via ssh-add -l and/or use with git (see below)
  • "filepath" = path to key file (eg. in powershell, $env:USERPROFILE\.ssh\my-key)

REMEMBER TO SET PASSPHRASE TO THE KEY FILE!!!

ssh-keygen -C comment -f filepath

Allow key on server

Manually

  1. client side: copy the public key contents to clipboard (manually or via type "c:\users\username\.ssh\my-key.pub" | clip)

  2. server side: add public key to server's authorized keys by editing C:\ProgramData\ssh\administrators_authorized_keys and appending your public key

  3. server side: grant permissions to Administrators group and SYSTEM user for the administrators_authorized_keys file

Via script

Execute this script on the client, after adjusting the variables values.

$publicKeyPath = "$env:USERPROFILE\.ssh\my-key.pub"
$serverUsername = "user"
$serverHostname = "remote.violinminds.com"
$serverPort = "22"

# Get the public key file generated previously on your client
$authorizedKey = Get-Content -Path $publicKeyPath

# Generate the PowerShell to be run remote that will copy the public key file generated previously on your client to the authorized_keys file on your server
$remotePowershell = "powershell Add-Content -Force -Path $env:ProgramData\ssh\administrators_authorized_keys -Value '$authorizedKey';icacls.exe ""$env:ProgramData\ssh\administrators_authorized_keys"" /inheritance:r /grant ""Administrators:F"" /grant ""SYSTEM:F"""

# Connect to your server and run the PowerShell using the $remotePowerShell variable
ssh ${serverUsername}@${serverHostname} -p${serverPort} $remotePowershell

SSH Agent setup

  1. setup the agent service to automatically start with Windows (see above); start the service
  2. add every key to the agent, one by one, via ssh-add; eg. in powershell: ssh-add $env:USERPROFILE\.ssh\my-key (private keys don't have ".pub" extension) (passphrase will be required)
  3. list added keys via: ssh-add -l

Test connection

Test connection via ssh -T <ssh-host> (replace "ssh-host" with your server's ip or URI).

If you wish you can add a welcome banner to the server so that you see a custom message every time you log onto it. Just edit the server's config (c:\ProgramData\ssh\sshd_config on the server's filesystem) and add/uncomment the Banner line specifying a path to a text file (eg. Banner c:\my_sshd_banner.txt). Then restart the ssh server to apply the new setting, and test the connection again; you will see your banner upon connecting.

Github setup

Common setup

  1. !!! When installing git for windows, remember to select "Use external OpenSSH" !!! image
  2. create keys for the client (see above)
    • for authentication, create a key with comment containing "git-auth", eg. in powershell ssh-keygen -C git-auth -f "$env:USERPROFILE\.ssh\git-auth"
    • for signing, create a key with comment containing "git-signing", eg. in powershell ssh-keygen -C git-signing -f "$env:USERPROFILE\.ssh\git-signing"
  3. add keys to your profile @ https://github.com/settings/keys (copy-paste both the public keys contents)

Authentication (cloning / pulling / pushing / etc)

Test auth via: ssh -T [email protected], it should print: "Hi username! You've successfully authenticated, but GitHub does not provide shell access.". If that's not the case and you get the error [email protected]: Permission denied (publickey)., debug with the -v or -vvv switches ("verbose"): ssh -vvvT [email protected]. See the Troubleshooting section for more help.

Now you should be able to clone a repository via: git clone [email protected]:violinminds/knowledgebass.git (get link in the repository page on Github by clicking the "<> Code" button and and selecting "SSH" in the clone section).

Visual Studio config

Thanks to the global git settings, Visual Studio should be already working correctly.

Visual Studio Code config

To configure vscode to use SSH instead of HTTPS, add "github.gitProtocol": "ssh", "remoteHub.gitProtocol": "ssh" to your settings.json file.

Commits signing

Configure git to always sign Github commits with your ssh key identified by the comment containing "git-signing" (run all commands in powershell):

OPTIONAL (not recommended): if you want, you can use a custom config file only for host "[email protected]": git config --global "includeIf.hasconfig:remote.*.url:[email protected]**/**.path" .github.gitconfig. If you do so, run the following commands replacing --global with --file $env:USERPROFILE/.github.gitconfig. PLEASE NOTE: if you do so, commits will be signed only after the "[email protected]" remote has been added, so initializing new repositories and immediately committing to them will create non-signed commits!

  • instruct git to use ssh instead of gpg: git config --global gpg.format ssh
  • force signing of all commits: git config --global commit.gpgsign true
  • force signing of all tags: git config --global tag.gpgsign true
  • command to retrieve public key from agent: git config --global gpg.ssh.defaultKeyCommand 'cmd /c "C:\\Windows\\System32\\OpenSSH\\ssh-add.exe" -L | findstr git-signing'

Now you can commit as usual, or by explicitly signing the commit via the -S parameter (git commit -S -m "message"); commits will always be signed by default.

Signature verification

You can (and should) verify whether your commits have been correctly signed or not.

On Github

Open the repository commits history (<repo url>/commits, eg. https://github.com/aetonsi/pwsh__Utils/commits/). If a commit is signed correctly with your registered signing key, you will see a green "Verified" label for the commit: image

Locally

Run: git log --show-signature. You will see that the commits appear as unverified and you will get an error:

error: gpg.ssh.allowedSignersFile needs to be configured and exist for ssh signature verification
commit 605862b7c393385266419b46f2409a5e019391c2 (HEAD -> master, origin/master)
No signature
Author: aetonsi <[email protected]>
Date:   Fri Jan 20 15:24:25 2023 +0100

    add util confirm
error: gpg.ssh.allowedSignersFile needs to be configured and exist for ssh signature verification

...

Just as Github knows a signature is valid by checking in its list of authorized keys, you also have to make a list of authorized keys for your local git installation. To do so, run the following commands (powershell):

git config --global gpg.ssh.allowedSignersFile "$env:USERPROFILE\.ssh\allowed_signers"

echo "$(git config --get user.email) $(type $env:USERPROFILE\.ssh\git-signing.pub)" >> "$env:USERPROFILE\.ssh\allowed_signers"

The file structure is simple: it simply contains a list of <email> <public key> rows, each one representing an authorized user.

Then you can verify your commits' signatures again and you will get "Good git signature for ...":

commit 605862b7c393385266419b46f2409a5e019391c2 (HEAD -> master, origin/master)
Good "git" signature for [email protected] with RSA key SHA256:5GiMEA805OT3GRyPCR+OJqiiPFvDomh7Kr3NGFUeSxI
Author: aetonsi <[email protected]>
Date:   Fri Jan 20 15:24:25 2023 +0100

    add util confirm

...

Visual Studio config

Thanks to the global git settings (gpg.ssh.defaultKeyCommand and core.sshCommand in particular), Visual Studio should be already working correctly.

Visual Studio Code config

If you want to be sure to enforce commit signing in vscode, add "git.enableCommitSigning": true to your settings.json file.

Enforce SSH transport protocol for git

To disallow any transport protocol except SSH (recommended for consistency), run:

git config --global protocol.http.allow never
git config --global protocol.https.allow never
git config --global protocol.git.allow never
git config --global protocol.file.allow never
git config --global protocol.ssh.allow always

Please note: some platforms (eg. Heroku) allow access only via a single protocol (eg. HTTPS). For those repositories, you have to allow the protocol you need: git config protocol.https.allow always. You will never be able to do a "clone" operation; instead, you will have to init an empty repository, run the aforementioned config command, add the remote, fetch, then checkout the branch you need with git checkout -b. You could create a git alias to simply this procedure, for example (powershell):

git config --global alias.clone-https "!f() { newdir=`"`$(basename `"`$1`")`" ; mkdir `"`$newdir`" ; cd `"`$newdir`" ; git init ; git config protocol.https.allow always ; git remote add origin `"`$1`" ; git fetch ; git checkout -b master origin/master ; }; f"
# then you can run:
git clone-https https://git.heroku.com/your-heroku-repo.git

Setup SSH Banner

Add/uncomment the Banner line in C:\ProgramData\ssh\sshd_config:

Banner c:\banner_to_show_when_sshing_-T.txt

Troubleshooting tips

  • verify that git is also loading the Github config file, by running git config -l --show-origin in a Github working copy

  • if you get the warning "@ WARNING: UNPROTECTED PRIVATE KEY FILE! @" when trying to use the keys, fix the private key(s) file(s) permissions to allow FULL CONTROL to the current user, SYSTEM and the Administrators group

  • if a repository was already cloned via HTTPS and you want to start working via SSH, change its remote via: git remote set-url origin [email protected]:violinminds/knowledgebass.git. To verify the current remotes, run: git remote -v

  • if you get an error, eg. "Permission denied (publickey). fatal: Could not read from remote repository.", to debug, you can add the -v switch to core.sshCommand setting in the git config to be more verbose (use -vvv to be even more verbose)

    • a possible problem might be that, for some reason, ssh is not using the agent's keys. In the verbose debug log, ssh reports a list of the keys it tries to use when connecting to an ssh host, which should also include the agent's keys. If the agent keys are missing, see the following Troubleshooting tips. Example of correct debug log:
      debug1: Will attempt key: git-auth RSA SHA256:yyyyyyyyyyyyyyyyyyyyyyyyyyyy agent
  debug1: Will attempt key: git-signing RSA SHA256:xxxxxxxxxxxxxxxxxxxxxxxxxxxx agent
  debug1: Will attempt key: C:\\Users\\username/.ssh/id_dsa
  debug1: Will attempt key: C:\\Users\\username/.ssh/id_ecdsa
  debug1: Will attempt key: C:\\Users\\username/.ssh/id_ecdsa_sk
  debug1: Will attempt key: C:\\Users\\username/.ssh/id_ed25519
  debug1: Will attempt key: C:\\Users\\username/.ssh/id_ed25519_sk
  debug1: Will attempt key: C:\\Users\\username/.ssh/id_xmss

  • if by debugging with a verbose core.sshCommand or simply by trying the authentication with ssh -vT [email protected] you see that ssh is not trying the agent's keys, it might be that the agent service is not running. Start it via sc start ssh-agent and try again

    • If the agent is running but the problem is still present, it might be that git is not using the system's OpenSSH suite. This might happen if you didn't select "Use external OpenSSH" during git setup. To verify this, you can either set core.sshCommand to where.exe ssh > ~/sshlocation.txt && notepad ~/sshlocation.txt && rm ~/sshlocation.txt then run a git command again (eg. git clone), or you can to run which ssh in git Bash; both are ways to determine which ssh binary git is trying to run. If it's not the OpenSSH binary (located in C:/WINDOWS/System32/OpenSSH), fix your PATH environment variable. If git is using its internal ssh (C:\Program Files\Git\usr\bin), reinstall git for windows and select "Use external OpenSSH"