

A system like proxmox backup server can do this scurely. There you can create a user that can only add new backups and read the existing ones, but cannot delete any or read anything else on the remote host.
Otherwise if you only care to protect the remote machine, then something like an ssh chroot jail would also work.












The benfit of tang is that you don’t store the secret on a shared server.
The server has a single keypair that it reuses for every client, and each client has thier own keypair.
The encryption key can only be recovered when the client and server perform thier handshake. And only the client gets the key, the server cannot see it.