Perry E. Metzger

@perrymetzger · Twitter · 2025-10-01 14:53 UTC

So, every time people propose fixing a social problem with security technology, the security people immediately shake their heads and say “I don’t think that’s possible”, the people insisting that it must be possible push it anyway, the security people then break the extremely expensive systems about fifteen minutes later and do some really devastating demos at security conferences that make the (experienced) audience laugh at how anyone could have imagined the idea would have worked in the first place, the people who proposed the impossible technology get angry and demand that Congress immediately pass laws repealing both mathematics and physics, and the cycle continues. In the current case, there’s essentially no way to do this. It’s a fractally broken idea. People have to edit images for one thing and there’s no way to maintain provenance through that. The public keys installed in image sensors will be easy for third parties to obtain to sign completely fake images. Keys embedded in sensors will themselves be easy to extract because you simply can’t make sufficiently secure hardware for a buck or two, certainly not hardware that can withstand even a modestly skilled home lab attack. (Yes, there are people who decap and scan chip dies at home. With cheap equipment. No, you can’t stop them.) Managing the provenance chain to do the verification will become unwieldy on end user devices. The images that your social media app confirms are real could be of an event that has nothing to do with what someone claims they are of even if they're images that were captured by a real image sensor. I could go on and on. The idea itself is broken. I can understand the demand that somehow it be possible to prove that an image came from the real world. Magic would make so much of life easier, but we don’t have magic. Guaranteeing provenance is not going to be possible. You are going to have to live with the fact that, as has been the case for decades now, you can’t trust images. I wish this was the first time that I have had to say something like this. It’s not even the fiftieth time. People who haven’t broken security systems on a regular basis (yes, I have) simply lack an intuition for what could work because they don’t have a developed adversarial mindset, and decades of experience say you can’t even learn that sort of mindset easily. People without that mindset routinely insist that something that is impossible must be easy. “Just do this obvious thing!” they say. But the obvious thing almost universally turns out to be unable to achieve what those people want it to achieve.