Hi, I’m running a ubuntu based backup server. And was wondering if there’s a simple way to encrypt my drives in case they get swiped or something by a break in. But also in a way that the computer can be restarted and decrypt the drive without me needing to stick a key in everytime. Any ideas? It seems basic but I’m not an expert on all these newfangled encryption terminology, so would like something idiot proof (by idiot proof, not idiot enough to lose/forget the decryption key)
You can actually unlock LUKS from another machine over SSH: https://www.cyberciti.biz/security/how-to-unlock-luks-using-dropbear-ssh-keys-remotely-in-linux/
I’m pretty happy with this solution
LUKS can use a TPM now.
Wait, how’s this gonna help? If someone swipes the machine, they also have the TPM. TPM only helps against someone reading the disks on another machine. TPM is only useful to protect data during physical access if the rest of the firmware/software stack is impenetrable. In practical terms this would mean locked UEFI, disabled alternate boot device, Secure Boot, locked GRUB, and locked logins. In effect the security of the data is transferred from the knowledge of a passphrase to the knowledge of a login password, and the attack surface is expanded across multiple systems that all have to be secure and configured correctly to not allow access prior to OS login.
I read it as external drives, as someone “swiping the drives” without having stolen the whole ass computer kinda requires that?
I agree that if someone steals the whole computer, you’re pretty fucked unless you have a password entered somewhere in the chain to actually do the decryption, but I mean, they explicitly didn’t want that.
I’m not sure there’s a good way to encrypt a system that’ll boot with no interaction (and thus has to be able to decrypt itself with no input) and prevent access if it’s stolen.
This is one of those ‘software security doesn’t matter if you can’t guarantee physical security’ meta-problems, probably.
Yeah, you’re right, if it’s meant as disks-only, then TPM is the easy solution.
I think SSH unlocked LUKS at boot might be a decent compromise, with the SSH server at a different physical location.
I mean, TPM-locked machine with all the other parts configured correctly should be reasonably secure. It would boot without interaction and be available on the network. It would require a sophisticated and motivated actor to find a vulnerability in one of the systems in the boot chain to get in. That’s probably good enough for preventing data leaks from theft. But the user has to make sure the whole boot chain is configured securely.
Do encrypted backups with Borgbackup or similar. That means the server never sees the plaintext or the decryption keys. The encryption happens on the client. Since it’s public-key encryption (separate keys for encryption and decryption), the client doesn’t need the decryption key either, except when restoring. So your backup can be automated without secret keys.
I worte a guide last year on how I do network bound encryption - that is the disk will automatically decrypt at boot if it’s connected to my home network, but not if the disk or machine is removed from my house. The advantage over the dropbear method is that you can set unattended upgrades to auto reboot your server whenever it installs security updates, and it’ll come back up with no manual intervention from you.
If you want simple you’ll have to manually decrypt each time it needs doing.
If you want it to be “automatic” then your best bet is something network based. A “simple” would be to just have a script ssh’s somewhere, pulls the decryption key, and then decrypts the disks. There’s plenty of flaws with this though as while a threat actor couldn’t swipe a single encrypted disk they could just log in as root, get your script, and pull the decryption key themselves.
The optimal solution would be to also encrypt the root partition but now you need to do network based decryption at boot which adds further complexity. I’ve previously used Clevis and Tang to do this.
I personally don’tencrypt my server root and only encrypt my data disks. Then ssh in on a reboot or power event and manually decrypt. It is the simplest and most secure option.
