Still, unique keys for each camera would lessen the risk of someone leaking a single code that undermines the whole system, as happened with DVDs.
And if an interested party wanted to steal a camera’s private key to fake an image’s provenance they’d need to get physical access to that very camera. Perhaps a state-sponsored group could contrive this (or intervene during manufacturing), but it is a challenge and an even bigger challenge for everyone else.
Physical access means all bets are off, but it’s not required for these attacks. If it’s got a way to communicate with the outside world, it can get hacked remotely. For example here’s an attack that silently took over iphones without the user doing anything. That was used for real to spy on many people, and Apple is pretty good at security. Most devices you own such as cameras with wifi will likely be far worse security-wise.
