Signal Secure Backups

Without paying for remote backups, can I just manage my own backup on my own hard drive, and restore it when I want to?

Yes! That has been supported for a long while. At least on Android, go to Settings -> Chats -> Chat Backups. Set up a schedule and a passphrase and a folder, and it will export your chats every day.

I do that and then sync that folder with another computer using SyncThing.

> I do that and then sync that folder with another computer using SyncThing.

AFAIK SyncThing only monitors for changes between files with matching names, and Signal stores each backup with a separate (timestamped) filename. Are you storing every day's backup individually, or do you have some tool for deduplicating?

Encrypted backups can't be deduplicated unless the encryption is flawed. There shouldn't be a way to tell that one Signal backup is somewhat related to another, unless you have the passphrase.

That also means that Syncthing can't do better than sending the full backup. But if you're syncing via wifi (e.g. at home) it's not really a problem anyway.

> Encrypted backups can't be deduplicated unless the encryption is flawed

This isn't an encryption problem; each device can only have one instance of Signal installed, and the latest backup (assuming it has terminated successfully) is a superset of the previous ones (aside from any messages that have dropped from retention, which you presumably don't want to be preserving, by definition).

"Deduplicate" in this context means ensuring that you only have N backups in your remote storage, rather than cumulatively storing every day.