The 5th amendment explicitly permits courts to issue warrants to seize evidence of a crime upon probable cause. YOU can not be compelled to testify against yourself. But your possessions certainly can be, if a judge believes there is probable cause that said possessions contain record of a crime. If you run someone over with your car and the ambulance crew notices you have a dash cam, I guarantee your car's getting impounded and the cops will ask for and receive a warrant pronto.
The purpose of this feature, and a large part of any computer's full disk encryption, is to defy warrants.
Using public/private key crypto for this is NOT pie in the sky wishful thinking, it is an absolute requirement. And "password-protected storage" isn't enough. If the dash cam is capable of playing back on its own screen, then it's not meaningfully encrypted.
I will offer, that pub/priv crypto is much slower than symetric, so the better way to implement this is to use seperate files for each minute with random symetric keys, and then journal those keys to a text file using pub/priv crypto and erase from memory after each minute has passed. To survive catastrophic failure, the symetric keys should be generated in batch several minutes beforehand, and sync'd to storage after the pub/prib encryption. Then they stay in ram until used. Design the hardware so that disconnecting power causes a reboot. Not even three letter agencies are going to be able to hack it in less than 60 seconds after pulling you out of the car. Wanna make it even better, figure out how to reboot it any time a door is opened.
And it's not just about the dash cam owner getting away with reckless driving. I've spent hours talking with attornies in my car. I've spoken highly sensitive passwords and information. I've discussed posessions of extraordinary value with trusted passengers. I'm not some flippant millenial happy to use uber and not own a car. My car is a secured space the integrity of which I depend on. If some dumb dash cam recorded that and some crackhead could just break a window and walk off with that information, lives could very realistically be lost over it.
And about "new users" coming in all the time and bringing this up... I'll mention, because I am one such new user.... I came here because it's the most obvious group of knowledgable dashcam users and makers. I didn't see the feature I require listed on the front of any product on amazon. So I came here for recommendations. I rather don't care if it's expensive. It has to be secure. And it can't be substantially larger on the window glass, but I WOULD tolerate if the cameras were all wired back to a computer module that I could put in or behind the glovebox in the dash area of the car. The less visible the cameras themselves are, the better in my mind since I don't want to attrack crackheads to break in and steal the damn cameras.
