But.. if the camera app automatically signs pics/vids, that would mean that a private key is available to the app without any passphrase (or one embedded in the app :O).. So why not just extract they key and sign your fake vid?
Well, for something like this the user's signing key itself would probably be managed by the OS, so not extractable. When the app is done editing, it asks the user via the OS to approve the result and the OS performs the signature. You could even embed a downsample of the original that came signed from the camera hardware.
If the key is managed by the OS but is inaccessible to the user, the concept would seem to be incompatible with free software operating systems. Also, if the camera app can have anything it "makes" approved, the app itself could take a deepfake video (from the web or device storage) and have the OS sign it.
The only way I see it working is if the key is "burnt-in" to in the camera hardware and any applications cannot MitM it.
Why would you assume it would be inaccessible to the user? I'd expect a key management interface at least. I guess I did say "not extractable", but I meant more that random apps don't have access to it directly, but they call an api to do the signing.
> the app itself could take a deepfake video and have the OS sign it
Note how I said "it asks the user via the OS to approve the result". I would expect a modal OS dialog to let the user review and approve the content before being signed and passed back to the app.
Thinking about it, there's actually nothing stopping this from happening on today's hardware using just application sandboxing. Substitute "OS" above with "Signing App" that does the same thing (accepts media signature requests from other apps, and opens dialog to request approval from user with a preview).
