I'd like to give my users some private network storage (private from me, ie. something encrypted at rest with keys that root cannot obtain).
Do you have any recommendations?
Ideally, it should be something where files are only decrypted on the client, but server-side decryption would be acceptable too as long as the server doesn't save the decryption keys to disk.
Before someone suggests that, I know I could just put lucks-encrypted disk images on the NAS, but I'd like the whole thing to have decent performance (the idea is to allow people to store their photos/videos, so some may have several GB of files).
edit:
Thanks everyone for your comments!
TLDR: cryfs
Turns out I was looking at the problem from the wrong point of view: I was looking at sftpgo and wondering what I could do on the server side, but you made me realise this is really a client issue (and a solved one at that).
Here's a few notes after investigating the matter:
- The use case is exactly the same as using client-side encryption with cloud storage (dropbox and those other things we self-hoster never use).
- As an admin I don't have to do anything to support this use case, except maybe guiding my users in choosing what solution to adopt.
- Most of the solutions (possibly all except cryfs?) encrypt file names and contents, leaking the directory structure and file size (meaning I could pretty much guess if they are storing their photos or... unsavory movies).
- F-droid has an Android app (called DroidFS) that support gocryptfs and cryfs
I'll recommend my users try cryfs before any other solution. Others that may be worth it looking at (in order): gocryptfs, cryptomator, securefs.
I'll recommend my users to avoid cryptomator if possible, despite its popularity: it's one of those commecrial open source projects with arbitrary limitations (5 seats, whatever that means) and may have nag screens or require people to migrate to some fork in the future.
ecryptfs is to be avoid at all costs, as it seems unamaintaned.
The host mounts no LUKS. The host just exports a network share via NFS. The client mounts that NFS share to a local mount pount. Then the client has a dir which actually resides on the host. So far completely standard NAS stuff. Then the client creates a file in that dir. E.g. secretcontainer.img. This file is then encrypted on the client using cryptsetup (LUKS). Then it's mounted on the client using LUKS. All the LUKS stuff happens on the client. The only interaction with the host is throgh NFS. The host just sees a file appear called secretcontainer.img on its storage. The same idea would work with VeraCrypt instead of LUKS. Or Cryptomator. Or anything else that can store encrypted data in file(s) in a directory.
LUKS can be used on a single file where the file acts as a disk device.
Also what I'm describing here is bog-standard Linux functionality that's existed at least for 2 decades. Nothing fancy. It's stuff that's good to know so I'd be happy to answer questions.
E:
The procedure on the client is roughly:
Once that's done, subsequent uses are:
Of course that can be automated further.
Just tested it in a local dir and it works fine. The only difference between that and the real scenario is whether
test.imgresides on a network mount or local disk. Since the network mounts behave like normal disks, everything else works the same. The only concern is what the performance would be, which depends on how the underlying network fs handles reads/writes totest.img. E.g. if you change 0.5MB, does it send that 0.5MB or does it rewrite the whole 1GB file. When reading, does it have to read the whole 1GB file or just parts of it as needed. Etc.Bud...been doing this for 20 years. Don't need your explainer.
The fact you didn't mention the barest of minimums in your comment if where the issue lies. You're just adding stacks on stacks of things by using any other network mount and having the user manage an encrypted image inside that mount. Also absent from what you were trying to explain. I'd work on that.
Point being, for a multi-user/tenant utility like OP is asking for, there are better tools for the job, of which I just named a couple standalone options. If they are running TrueNAS, Synology, or QNAP, or even NextCloud, there are already built-ins for this purpose, and apps to match.
If not, any of the other solutions I mentioned are much better suited for the use-case, especially, and if not only because, OP specifically said they DID NOT want exactly what you're describing.
I described the procedure step-by-step mentioning each layer. That's the best I could do.
OP said they're worried about performance with this solution. Hence why my first response addressed the performance issue. The rest was responding to you (and anyone else who is reading) since you thought that is not an E2E solution. I tried explaining why it's client-side encryption and no keys are stored on the host.