Installing SFTP/SSH Server on Windows using OpenSSH

Recently, Microsoft has released a port of OpenSSH for Windows. You can use the package to set up an SFTP/SSH server on Windows.

Installing SFTP/SSH Server
- On Windows 10 version 1803 and newer
- On earlier versions of Windows
Configuring SSH server
Setting up SSH public key authentication
Connecting to the server
- Finding Host Key
- Connecting
Further reading

Installing SFTP/SSH Server

On Windows 10 version 1803 and newer

In Settings app, go to Apps > Apps & features > Manage optional features.
Locate “OpenSSH server” feature, expand it, and select Install.

Binaries are installed to %WINDIR%\System32\OpenSSH. Configuration file (sshd_config) and host keys are installed to %ProgramData%\ssh (only after the server is started for the first time).

You may still want to use the following manual installation if you want to install a newer version of OpenSSH than the one built into Windows 10.

On earlier versions of Windows

Download the latest OpenSSH for Windows binaries (package OpenSSH-Win64.zip or OpenSSH-Win32.zip)
As the Administrator, extract the package to C:\Program Files\OpenSSH

As the Administrator, install sshd and ssh-agent services:

powershell.exe -ExecutionPolicy Bypass -File install-sshd.ps1

Configuring SSH server

Allow incoming connections to SSH server in Windows Firewall:
- When installed as an optional feature, the firewall rule “OpenSSH SSH Server (sshd)” should have been created automatically. If not, proceed to create and enable the rule as follows.
- Either run the following PowerShell command as the Administrator:
```
New-NetFirewallRule -Name sshd -DisplayName 'OpenSSH SSH Server' -Enabled True -Direction Inbound -Protocol TCP -Action Allow -LocalPort 22 -Program "C:\System32\OpenSSH\sshd.exe"
```
  Replace C:\System32\OpenSSH\sshd.exe with the actual path to the sshd.exe (C:\Program Files\OpenSSH\ssh.exe, had you followed the manual installation instructions above).
- or go to Control Panel > System and Security > Windows Defender Firewall1 > Advanced Settings > Inbound Rules and add a new rule for port 22.
Start the service and/or configure automatic start:
- Go to Control Panel > System and Security > Administrative Tools and open Services. Locate OpenSSH SSH Server service.
- If you want the server to start automatically when your machine is started: Go to Action > Properties. In the Properties dialog, change Startup type to Automatic and confirm.
- Start the OpenSSH SSH Server service by clicking the Start the service.

These instructions are partially based on the official deployment instructions.

Setting up SSH public key authentication

Follow a generic guide for Setting up SSH public key authentication in *nix OpenSSH server, with the following difference:

Create the .ssh folder (for the authorized_keys file) in your Windows account profile folder (typically in C:\Users\username\.ssh).2
For permissions to the .ssh folder and the authorized_keys file, what matters are Windows ACL permissions, not simple *nix permissions. Set the ACL so that the respective Windows account is the owner of the folder and the file and is the only account that has to write access to them. The account that runs OpenSSH SSH Server service (typically SYSTEM or sshd) needs to have read access to the file.
Though, with the default Win32-OpenSSH configuration there is an exception set in sshd_config for accounts in Administrators group. For these, the server uses a different location for the authorized keys file: %ALLUSERSPROFILE%\ssh\administrators_authorized_keys (i.e. typically C:\ProgramData\ssh\administrators_authorized_keys).

Connecting to the server

Finding Host Key

Before the first connection, find out the fingerprint of the server’s host key by using ssh-keygen.exe for each file.

In Windows command-prompt, use:

for %f in (%ProgramData%\ssh\ssh_host_*_key) do @%WINDIR%\System32\OpenSSH\ssh-keygen.exe -l -f "%f"

Replace %WINDIR%\System32 with %ProgramFiles%, if appropriate.

In PowerShell, use:

Get-ChildItem $env:ProgramData\ssh\ssh_host_*_key | ForEach-Object { . $env:WINDIR\System32\OpenSSH\ssh-keygen.exe -l -f $_ }

Replace $env:WINDIR\System32 with $env:ProgramFiles, if appropriate.

You will get an output like this:

C:\Windows\System32\OpenSSH>for %f in (%ProgramData%\ssh\ssh_host_*_key) do @%WINDIR%\System32\OpenSSH\ssh-keygen.exe -l -f "%f"
1024 SHA256:K1kYcE7GHAqHLNPBaGVLOYBQif04VLOQN9kDbiLW/eE martin@example (DSA)
256 SHA256:7pFXY/Ad3itb6+fLlNwU3zc6X6o/ZmV3/mfyRnE46xg martin@example (ECDSA)
256 SHA256:KFi18tCRGsQmxMPioKvg0flaFI9aI/ebXfIDIOgIVGU martin@example (ED25519)
2048 SHA256:z6YYzqGiAb1FN55jOf/f4fqR1IJvpXlKxaZXRtP2mX8 martin@example (RSA)

Connecting

Start WinSCP. Login dialog will appear. On the dialog:

Make sure New site node is selected.
On New site node, make sure the SFTP protocol is selected.
Enter your machine/server IP address (or a hostname) into the Host name box.
Enter your Windows account name to the User name box. It might have to be entered in the format user@domain if running on a domain.
For a public key authentication:
- Press the Advanced button to open Advanced site settings dialog and go to SSH > Authentication page.
- In Private key file box select your private key file.
- Submit Advanced site settings dialog with the OK button.
For a password authentication:
- Enter your Windows account password to the Password box.
- If your Windows account does not have a password, you cannot authenticate with the password authentication (i.e. with an empty password), you need to use the public key authentication.
Save your site settings using the Save button.
Login using Login button.
Verify the host key by comparing fingerprints with those collected before (see above).

If you cannot authenticate to the server and use Windows 10 Developer mode, make sure that your OpenSSH server does not conflict with an internal SSH server used by the Developer mode. You may need to turn off the SSH Server Broker and SSH Server Proxy Windows services. Or run your OpenSSH server on a different port than 22.