Hector Martin

Am I tripping or if you upgrade Signal Desktop, it saves all your messages in plain text (messages.json) + attachments locally so you can re-import them in the newer version? #fail #wtf

There is no magical pixie dust encryption algorithm that will protect your messages in such a way that whatever new version of Signal can access them but no other app or user can (on a desktop). If you have local access it's game over.

How about a non-magical average good encryption scheme where messages stores are encrypted using a password as salt? I don't know why you need to be condescending or exasperated about something as basic as encryption at rest.

What's the point? So you save the messages encrypted, import them, and then what? They're going to be decrypted to be useful, with credentials that any other app can hijack out of the running Signal instance even if they're encrypted "at rest".

If you encrypt at rest with a password based key (using KDF) that you don't store anywhere, and decrypt only chunks of the data at rest to store in memory, then you are limiting the attack surface. Also, this helps against device theft where they don't conrol your running app

Unless you want to input your password for every single message you view, the key has to be in memory while you use the app, at which point any other process can grab it.

'Chunks' can mean 'your last 5 days of messages'. Scrolling further would require a retype. But even if it is kept in memory, it's still good against device theft.

We already have FDE to protect against device theft. Doing it in the app would require you to log in on every boot. It makes a lot more sense to have FDE for the whole system rather than each app implementing its own thing.