What is the payoff here? Is the projector sold below cost and is the manufacturer recouping that via the cartridges? If not, what's the loss to them?

Regarding the proposed mitigations, I'm very doubtful on whether they would substantially change anything here:

> Use real crypto (AES-128 or lightweight stream) and make the cartridge carry per-title key (or an IV)

> Copying now requires cloning/extracting the original token secrets.

Sounds like a great idea, and fortunately we don't even need to speculate about whether it would work: Nintendo did this with Amiibo.

> If true anti-cloning matters, this requires an authenticated token (DESFire / NTAG 424 DNA class).

And where do you securely store the validation key for a symmetric encryption/authentication scheme? This would require adding a SAM to the projector as well.

The "use non-default NFC keys" suggestion shares the same problem: Where would you securely store these?

It would save the world so, so much grief and cheap insecure consumer devices. I will flip my lid if I see another kiddy-cam on Shodan.

For example, what kind of moron would put a secret you mustn't learn right next to data you can choose? A good solution wouldn't care, but surely a bad solution where that would cause a problem would never encounter real world scenarios where.... oh right HTTP Cookies

Good solutions won't lose security from repeating transactions, but while accidents might cause one or two repetitions surely no real world systems would need to withstand millions of... oh yeah, Javascript loops exist

Unpopular opinion here: but this article is perfect proof of concept that when trying to take something to market you need a non technical person put the brakes on some technical teams.