Windows 10/11 PowerShell Script to create and add SSH keys to a Linux server

use_ssh_keys.ps1

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# https://github.com/1x24
# 1x24 AT tuta.io
# March 31, 2023
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# This PowerShell script checks if you have SSH keys on your Windows 10 or Windows 11 machine.
# If you do not have the SSH keys, it generates a modern one for you.
# In either case, it copies the key to your server and makes some configuration changes to make it easy to login with the keys.
# Save then use as follows: 
#   (1) In Windows Explorer, open the folder where this script use_ssh_keys.ps1 is saved 
#   (2) Press Shift+F10 and choose "Open Powershell window here". This is the easiest way. 
#       	Don't have function keys? Then you can `Shift + Right-click` and select "Open Powershell window here".
#       	Note that in some versions of Windows, after that Shift+Right click you need to select 
#			"Show more options" before you can launch PowerShell from there.
#   (3) Inside the Powershell window run the script as follows, substituting in your server username (to replace USERNAME), server host (to replace MY.SERVER.HOST) 
#		    and the server port to replace SERVER_SSH_PORT (unless told otherwise, use the number 22)
#       PowerShell -ExecutionPolicy Bypass -file .\use_ssh_keys.ps1 -Username USERNAME -ServerHost MY.SERVER.HOST -ServerPort SERVER_SSH_PORT
#   (4) The script is going to ask you for a passphrase. You may simply press enter here.
#	  	   N.B. The passphrase secures your new key, but if you forget the password the key becomes unusable. I recommend pressing enter here. Do it twice.
#   (5) Now the script will ask you for your SSH password. Enter the password as requested, and the script will finish its process.
#   (6) From now on you can simply open PowerShell (see step 2) and run ssh MY.SERVER.HOST (no need for PuTTY or plink.exe) e.g. ssh fancy.server.com 
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param (
    [Parameter(Mandatory=$true)] [string] $Username,
    [Parameter(Mandatory=$true)] [string] $ServerHost,
    [Parameter(Mandatory=$true)] [int] $ServerPort
)

try {
    $keysFound = $false
    $homeDir = [Environment]::GetFolderPath('UserProfile')
    $sshDir = Join-Path $homeDir ".ssh"

    # Default key type and path
    $keyType = "ed25519"
    $keyPath = Join-Path $sshDir "id_$keyType.pub"
    $keyPathNoPub = Join-Path $sshDir "id_$keyType"

    # Check for existing keys in the common locations
    foreach ($potentialKeyType in @("rsa")) {
        $potentialKeyPath = Join-Path $sshDir "id_$potentialKeyType.pub"
	  $potentialKeyPathNoPub = Join-Path $sshDir "id_$potentialKeyType"
        if (Test-Path $potentialKeyPath) {
            $keysFound = $true
            $keyType = $potentialKeyType
            $keyPath = $potentialKeyPath
		$keyPathNoPub = $potentialKeyPathNoPub
            break
        }
    }

    # Generate a new SSH key if none are found
    if (-not $keysFound) {
        Write-Host "No SSH keys found. Generating a new one..."
        $keyType = "rsa"
        $keyPathNoPub = Join-Path $sshDir "id_$keyType"
        $keyPath = $keyPathNoPub + ".pub"
        ssh-keygen -o -t ed25519 -f $keyPathNoPub -q
    }

    # Copy the key to the remote server
    Write-Host "Copying SSH key to the remote server..."

    $sshCommands = "mkdir -p ~/.ssh && chmod 700 ~/.ssh && cat >> ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys"    
    type $keyPath | ssh -o StrictHostKeyChecking=no -o PreferredAuthentications=password -o PubkeyAuthentication=no `"$Username@$ServerHost`" $sshCommands

    # Append configuration to the local SSH config file
    $sshConfig = Join-Path $sshDir "config"
    Write-Host "Appending configuration to the local SSH config file..."

    if (-not (Test-Path $sshConfig)) {
        New-Item -ItemType File -Path $sshConfig -Force | Out-Null
    }

@"
Host $ServerHost
  Hostname $ServerHost
  User $Username
  Port $ServerPort
  IdentityFile $($keyPath -replace ".pub$","")
  PreferredAuthentications publickey
  GSSAPIAuthentication no
  ChallengeResponseAuthentication no
  HashKnownHosts no
  KbdInteractiveAuthentication no
  TCPKeepAlive yes
  ServerAliveInterval 25
  ServerAliveCountMax 600
"@ | Add-Content -Path $sshConfig


    Write-Host "Done! Press any key to exit."
    $host.UI.RawUI.ReadKey("NoEcho,IncludeKeyDown") | Out-Null
}
catch {
    Write-Host "Error: $($_.Exception.Message)"
    Write-Host "Press any key to exit."
    $host.UI.RawUI.ReadKey("NoEcho,IncludeKeyDown") | Out-Null
}