powershell – nullteilerfrei

I have a Windows VM that can has an internet connection that acts as a tunnel into a VPN, and this VM is supposed to share this internet connection with the host. This works perfectly in principle: On that Windows VM, I have a network interface named Outbound which represents the VPN connection, and an interface named Gateway which represents the connection that is shared with the host. I use Windows Internet Connection Sharing (ICS) to provide routing to the Gateway interface via Outbound. For reasons unknown to me, however, this sometimes just breaks and the only way to get it running again is to simply disable ICS on the Outbound interface and re-enable it. Doing this through the UI every time became annoying, so I researched how to do it programmatically. There is [a great superuser answer](https://superuser.com/a/649183/222330) which provides _almost_ all the details you need, but not quite. Do you want to know more?

I am writing a backup script which is supposed to backup data to a remote server, encrypted, and run as a scheduled task on a Windows machine. If you want all of that, you will have to store the encryption key somewhere. Instead of storing the password in plaintext, I had the idea to use the [Data Protection API]. Initially worried that I might have to write a wrapper for [CryptProtectData] myself, I quickly found the decent looking github project [DPAPIbridge]. Ultimately however, I figured out that Powershell can do all things. Presenting vault.ps1:

Param(
  [string] $StoreSecret,
  [Parameter(Mandatory=$True,Position=0)]
  [string] $filename )
[void] [Reflection.Assembly]::LoadWithPartialName("System.Security")
$scope = [System.Security.Cryptography.DataProtectionScope]::CurrentUser
if ($StoreSecret -eq "") {
  $data = Get-Content $filename
  $ciphertext = [System.Convert]::FromBase64String($data)
  $plaintext = [System.Security.Cryptography.ProtectedData]::Unprotect(
    $ciphertext, $null, $scope )
  [System.Text.UTF8Encoding]::UTF8.GetString($plaintext)
} else {
  $plaintext = [System.Text.UTF8Encoding]::UTF8.GetBytes($StoreSecret)
  $ciphertext = [System.Security.Cryptography.ProtectedData]::Protect(
    $plaintext, $null, $scope )  
  [System.Convert]::ToBase64String($ciphertext) > $filename
}

This script can be run as vault.ps1 [-StoreSecret SECRET] FILE. If the optional argument is present, it will store a protected blob containing SECRET in FILE, otherwise it will read a blob of protected data from FILE and print the enclosed secret string. [DPAPIbridge]: https://github.com/vincepare/DPAPIbridge [Data Protection API]: https://msdn.microsoft.com/en-us/library/ms995355.aspx [CryptProtectData]: https://msdn.microsoft.com/de-de/library/windows/desktop/aa380261(v=vs.85).aspx [Borg]: https://borgbackup.readthedocs.io/en/1.1.2/usage/general.html?highlight=borg_passcommand#environment-variables

Programmatic Internet Connection Sharing

Powershell DPAPI Script