11 mo. ago • 100%

Remote solution to decrypt disk at boot

Hi there ! I have a little box at home, hosting some little services for personal use under freebsd with a full disk encryption (geli). I'm never at home and long power outage often occurs so I always need to come back home to type my passphrase to decrypt the disk.

I was searching this week a solution to do it remotely and found the "poor-guy-kvm" solutions turning a Raspberry like board (beaglebone black in my case) in a hid keyboard. It works fine once the computer has booted but once reboot when the passphrase is asked before it loads the loader menu, nothing. When I plug an ordinary USB keyboard I can type my passphrase so USB module is loaded.

Am I missing something ? Am I trying something impossible ?

(I could've asked on freebsd forum but... Have to suscribe, presentation, etc... Long journey)

40 comments

Hi, Why not to do little bit diffrently?

Server boots into unencrypted kernel with ssh server (it has just that ssh server)

Then you connect remotely via ssh and provide password (unlock encrypted disks etc)

Then system boots to encrypted environment which you unlocked at step 2

profit

No second pc/raspberry is required

I have this done with luks on Debian: https://hamy.io/post/0009/how-to-install-luks-encrypted-ubuntu-18.04.x-server-and-enable-remote-unlocking/ I think you can adapt something similar to your freebsd

Quick google search found:

https://forums.freebsd.org/threads/encrypted-root-with-unencrypted-preboot-and-reboot-r.74378/

https://github.com/Sec42/freebsd-remote-crypto
16
- Shit, i totally missed this one, maybe not searching with good keywords... Thanks a lot, I've read fast for the moment so it doesn't seems to be fully encrypted but scenario in the forum and solution proposed can answer my needs (sorry for bad English ). Thanks !
  
  5
  
  The key to a good search is to know what your are looking for.
  
  If you know what you are looking for
  I know how you feel brother.
  At least we have the awesome members of the community showing us the other options!
  
  3
I'm not sure how it'd work for freebsd, but on Linux, you can get sshd running in your initrd. You can even go as far as getting an onion service running in your initrd, and using that for remote access.

12
- Yeah someone already told Me that some years ago (yeah, years ago...) but it doesn't work exactly like that with freebsd , it's possible but not full encrypted disk solution . thanks for your answet
  
  2
If you have a TPM you can use secure boot (custom keys) to allow Linux to decrypt itself if nothing has changed.

11
- Didn't know this thing, I will check about that, thanks !
  
  2
- What do you mean by if nothing has changed? Wouldnt this mean someone could physically steal the machine and then boot it up somewhere else and it'd auto decrypt itself?
  
  1
  
  Yes. That is possible. However if the hardware configuration/software configuration changes the TPM should trip and prevent decryption.
  
  The attackers would have to break you ssh/terminal/lock screen/other insecure software. However code injection should be impossible because you used custom secure boot keys and ideally a signed unified kernel image. (Can't even change kernel params without tripping TPM.)
  
  You would not be safe if they did a bus listening attack or if your shell pwd is not safe. If that is your threat vector this may not be a good option for you.
  
  5
I have a box at home .... I'm never at home.

How is this your home? Please resolve this mystery so I can find sleep again.

9
- I have not said "I have a box at my home" , just "at home" ;)
  
  3
Not sure about FreeBSD but under Linux I have used SSH based solutions in the past, specifically dracut-sshd to call systemd-tty-ask-password-agent and of course some early network configuration.

8
- Yeah someone already told Me that some years ago (yeah, years ago...) but it doesn't work exactly like that with freebsd , it's possible but not full encrypted disk solution . thanks for your answer
  
  1
I'm using encrypted ZFS as the root partition on my server and I've (mostly) followed the instructions in point #15 from here: https://openzfs.github.io/openzfs-docs/Getting%20Started/Debian/Debian%20Bookworm%20Root%20on%20ZFS.html

This starts dropbear as an SSH server that only has a single task: when someone logs in to it they get asked for the decryption key of the root partition.

I suspect that this could be adopted to whatever encryption mechanism you use.

I didn't follow it exactly, because I didn't want the "real" SSH host keys of the host to be accessible unencrypted in the initrd, so the "locked host" has a different SSH host key than when it is fully booted, which is preferred for me.

7
- I've read that freebsd 14 proposed zfs native encryption, so it could worked. Maybe it's time to upgrade, I will see. Thanks !
  
  3
Have you looked into policy-based decryption? Here's an knowledge base page on the RHEL customer portal that goes over it well. I'm not sure if this will work on freebsd but it does offer a solution that allows for zero-touch reboots.

4
- Oh interesting, I will read that back to my computer , thanks !
  
  1
- Oh interesting, I will read that back to my computer , thanks !
  
  1
I'm in the market for a similar solution. Is the BeagleBone being powered via USB? If so, it might be trying to pull more current than the USB stack will allow at that point. Can you debug the board while it's in the non-working state? Also, does it present as a single HID device?

4
- Yes the beaglebone black is currently powered by USB. Unfortunately I am not able to debug the board while it's not working due to my lack of skill... I don't know how to do... Maybe I can read dmesg on the bbb for a message stating this nonworking state while it asks for passphrase on the PC for a first step... Yes once it's booted, freebsd see it as a single hid device, just a hid device
  
  1
You gave some options

TPM 2 based disk encryption. This is basically what bitlocker does, but it isn't great. It uses an encryption key stored on your TPM chip, that shouldn't ever be accessible to be exported. This means the disk should only be decryptable in the machine it's in. That in conjunction with secure boot can give you some guarantees that the only way to access data is through the the computer itself (no pulling the disk first). The issue is there are many potential vulnerabilities that could subvert this, logoFAIL being the most recent.

You could setup a proper KVM. The two gotos are PiKVM and TinyPilot. Jeff Geerling did a good video on these. It'll cost a few 100 bucks but can definitely be worth it. You might consider a motherboard with a builtin KVM in your next build too.

Setup NBDE (Network Bound Disk Encryption). This is pretty new, but what I'm planning to move to. Redhat has an implementation with Tang & Clevis (server and clients). You might be able to eventually use Clevis with other alternative backend too.
4
- Thanks for your answer ! Someone already mention TPM, I will check about that when I will have free time. Already try pikvm and tinypilot with no success unfortunately.. Didn't know NBSDE, will take a look too !
  
  1
I think you are over thinking it. Most remote solutions like rustdesk and moonlight allow you to remotely log in.

Another thought is you could setup cockpit so you can control it remotely if everything else fails

3
You could buy a remote KVM device. The serial port of your target box connects to that and the KVM connects to the internet. With that, you can watch the device during boot and access the console remotely.

I used to run a web hosting business and we used those. I have not shopped for a personal one, but surely there must be old and used ones for sale.

Bonus: our hosting business ran on FreeBSD so I can confirm there was no problem there. Because it’s a serial connection no OS support is required.

3
- Hmm I've read it's expensive but never verified I admit it. And no serial port on my box... Will check the price of new and second hand device
  
  2
Did you try this: https://github.com/touchgadget/usbkwa ?

I use this to unlock Windows when I WOL it.

3
- Hmm seems to be hid keyboard "emulator" too. Having tried this kind of solution makes me think I have a problem with the hid module at boot so I will maybe abandoned this solution, will see. Thanks for your answer !
  
  1
Like someone already mentioned, you can use dracut-ssh for rpm-based distros or dropbear-initramfs for deb-based distros. My idea would be to use debian as host and virtualize or dockerize the freebsd system/software part.

2
- Thanks for your answer but... I like freebsd as a host
  
  2
  
  Tried to help :P What's your take on using freebsd instead of linux? More security?
  
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Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters	More Letters
IP	Internet Protocol
PCIe	Peripheral Component Interconnect Express
SSH	Secure Shell for remote terminal access
ZFS	Solaris/Linux filesystem focusing on data integrity

4 acronyms in this thread; the most compressed thread commented on today has 12 acronyms.

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