Best option for secure cloud file sync

Question

I would like to sync my files, as dropbox does for example. However, I want my files to be very secure. The main things I want are for it to be secure, 'just work' without hassle, and reasonably fast.

Options I am considering:

• Local encryption such as Veracrypt/Truecrypt with Dropbox sync or equivalent.
• Rclone encrypted sync to unencrypted cloud such as Dropbox.
• mega.io, icedrive.net, tresorit.com

My constraints are:

1. Content is "large" in that I cannot resync the whole content every change.
2. I am using Linux.
3. It must be a cloud service available over the public internet (I don't want to host / maintain my own service / hardware).
4. The files will be synced to multiple computers I own.
5. The files should be continually automatically synced to minimize conflicts (ie. not manually triggered).
6. Any installed software is open source.
7. I don't trust the cloud storage provider to keep stored data private on their systems.
8. The solution should not require the local files be stored encrypted (ie. if the password is lost or software breaks local files are still accessible).

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Bonus nice to have constraints:

1. Ideally I would like good OS integration. ie. Sync starts on system start, standard packages with provided updates, so I don't have to write my own scripts which may get out of date and break.
2. Occasionally I edit files in offline locations leading to conflicts. The system should be able to handle this. Software I have used in the past renames one of the files to indicate the conflict and that is a good solution.
3. Some files are "large" in that I would prefer not to resync the whole file if a small change is made.

From what I have read, there is no perfect answer today. To make this question more answerable, just saying which of the options I have listed is best (or worst) for my requirements would be a great answer. For example, if the answer is none are truly secure, but mega.io security is at least as good as any other option, plus it has change conflict handling, then I would use mega.io.

I think local encrypted volume, unencrypted cloud is not so good for handling change conflicts?

I don't mind paying for the service. The things I am storing are things like business information. I won't die if they get stolen.

Related questions:

• https://security.stackexchange.com/questions/153180/is-it-safe-to-have-a-truecrypt-container-file-synced-with-dropbox
• https://security.stackexchange.com/questions/150837/keep-encrypted-files-in-sync-on-a-cloud-service-without-having-to-upload-an-ent

Answer 1

Check out Cryptomator. I'm not sure if it's suitable for large files, but from a security perspective, the program seems pretty good.

Answer 2

Check out SyncThing. Although you mentioned Linux, if you (or anyone who will be reading this) will need to run it on a Windows machine, use this packaging of it, which make things much easier to setup: SyncTrayzor.

I believe it will check all of your boxes:

• #1 syncs only blocks that have changed.
• #2 Multi-platform, basically runs on everything mobile, pc etc.
• #4 The more computers you have, the better bandwidth you'll have - as it uses a bittorrent-like protocol
• #5 Once the deamon is running, it syncs all endpoints continually.
• #6 Completely open-source

Note that #3 and #7 are somewhat contradictory in your requirements, but I still think this is the solution you are looking for:

• #3 you can run this on any VPS and setup is rather easy, especially if using a dockerised option
• #7 you DON'T need a cloud provider here, as there is no server involved, unless you want one (#3). The clients will sync between themselves without involving 'a server'.

Hope you find this helpful.