I'm a bit confused regarding the order of things to make this happen.

This is what I had in mind:

1 - Generate CA public and private key.

2 - Use CA Public Key with SFTP server (TrustedUserCAKeys).

3 - Generate a user private + public key.

4 - Sign user private key using CA.

5 - Connect to the SFTP server using the private key, username and winscp.

Should this work?

1 Answer 1


CAs sign the public key (producing a certificate). They never see the signee's private key.

Besides that, the workflow seems correct, except for the WinSCP part.

The certificates used by TrustedUserCAKeys are a format invented by OpenSSH. Currently no other software supports this kind of certificate authentication – here's the PuTTY wishlist entry for them. Because WinSCP uses PuTTY as its SSH core, it does not have OpenSSH certificate support, and won't have it until PuTTY does.

  • I'm awake of that. It means that I will have to convert the key to a ppk format, which WINSCP offers right out of the box as it detects something else.
    – JustAGuy
    Nov 15, 2018 at 13:46
  • I guess I'll have to give it a go now :) Cheers.
    – JustAGuy
    Nov 15, 2018 at 13:46
  • I am not talking about the OpenSSH key format. Converting the key alone gives you nothing, because the client still won't be able to send the signed certificate to the server.
    – user1686
    Nov 15, 2018 at 13:47
  • That sounds strange... If the conversion is useless then why is it offering it automatically? Better yet, what would it take to do it right?
    – JustAGuy
    Nov 15, 2018 at 13:52
  • 1
    @JustAGuy There's Microsoft build of OpenSSH for Windows. Nov 15, 2018 at 15:12

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