Hacker News Reader

Comment by ndjshe3838 | Hacker News Reader

Would it be possible for cameras to have a hardware private key?

And then sign the images in hardware so that you can prove an image came from a specific camera and hasn’t been altered?

View on HN

It's already implemented in a limited number of cameras recently.

A hardware key proves which camera it came from, and a blockchain hash proves at least when the camera first connected to the internet after taking the photo. So, if anyone tries to claim your photo as their own, you need only point to the blockchain to prove it's actually yours. It also proves you didn't use any beauty filters outside the camera hardware security bubble.

https://news.adobe.com/news/news-details/2022/Adobe-Partners...

I predict it's going to go mainstream in a new iPhone model eventually. Consumers will become sold on the idea of authenticity. They are sick of fakes and filters, but didn't yet have any way to prove something is real.

Won't work. With enough resources it's always possible to get secrets out of hardware. Once compromised then every video and photo ever taken by that camera model can no longer be trusted to be authentic on signature alone.

Photo/video signing in hardware might actually make things worse by creating a false sense of security. It's better for people to question everything they see rather than trust everything they see.

Not really. It is inevitable such a system would lead to people spoofing the sensor to get fake images signed.

I think the solution to this could be the "web of trust" - as used with PGP. Everyone can sign their images with their private keys. Whether you think those images are trustworthy then depends on who else trusts that. For example, you could have some newspapers verify/trust their journalists camera's. And you could trust your friends camera's etc.

It’s not so easy to attack secure hardware. It won’t be an option for the vast majority of deep fake producers.

it is very easy to do - point your camera and record a video that is fake - bingo, the video of the video is signed as being real.

Yes, but it seems like clever people would not have trouble bypassing this. Just take a picture of a picture.

Thats not really bypassing it. The intention of the digital signature is "I trust John at AP, and this picture has a digital signature stating that this photo is taken by him, so I trust that its valid". You taking a photo of a photo just means that we now have a photo with your signature in it, and I never trusted you in the first place. To bypass it you have to trick John into faking a picture, or steal his cammera.

That's true but then why does it need to be a hardware backed key as part of the camera?

It will be people who need to learn how to sign and encrypt and manage their keys.

Because that proves you didn’t photoshop it after taking it or sign an AI generated image

That's unrealistic in practice. What if the camera manufacturer or an employee of the camera manufacturer messes with it?

I don't believe it will be possible in practice to "granularize" trust like that. You trust a person or an institution (a person is already more ideal though). Going even further will not work in practice.

There's no need for that to be done on the camera then. John's photo manager can just add a PGP signature from his laptop. Except in practice this isn't needed. The fact that it was posted by John on the AP website is enough proof

This has already been a thing for quite a while and all the major camera manufacturers have or are working on some solution for cryptographic provenance.

https://www.dpreview.com/news/9855773515/sony-associated-pre...

Betting it'll be something like Cinavia, but for images and where the embedded data is a key instead of just a simple 1,2,3,4 code. With high color depths, such as greater than 8 bit, there's probably enough "dataspace" to embed data somehow (e.g. imagine embedding a data stream in a band above 20KHz for audio, it can be part of a 22KHz WAV file, for example, but won't be heard at all). The encoding wouldn't survive the situation where a picture is taken of a picture at a lower color depth, but that's probably OK.

What you describe is called steganography. It's a very old technique, and the implications in the [lossy] digital realm are reasonably well-understood.

Here's some code that can be played with that relates to steganography in images: https://github.com/RoliSoft/Steganography/tree/master

Sounds risky if you're taking pictures of stuff the government doesn't want you to.

I doubt they'd do it via this system. It should be easy to strip this metadata, in fact that is essentially a requirement to make the photo readable on image viewers unaware of it

However if it came out that manufacturers were secretly storing a "fingerprint" of the noise profile of each image sensor and sharing it with the government, I'm afraid I wouldn't be entirely surprised

Remember https://en.wikipedia.org/wiki/Machine_Identification_Code

A photo signed as an authentic iPhone image wouldn’t completely pinpoint the photographer, but would be good evidence that the image is authentic.

Over any period of time, no probably not. If the algorithm is simple as "This was signed by an iphone" then you have a fleet of a billion+ iphones that all must remain secure and unbroken for the entire time this fleet of phones exist trends to unlikely. Given time and motivation all systems are broken.

A much harder to break system is one uses a secret only exists on each individual phone + the generic algorithm that iphones use, but this comes back to individuals being traced.

> uses a secret only exists on each individual phone

There is actually a way to prevent individuals from being traced while having a strong membership proof. This can be achieved by issuing signatures on a relative generator created in an exponentiation mix together with a set of output pseudonyms. One can picture it as strands braided together where it is hard to trace the link between the input and output strands, while it is very easy to tell that such a link exists.

More on that can be found on:

https://github.com/PeaceFounder/ShuffleProofs.jl

It will be interesting to see what solutions people will come up with to support cropping images and videos. Perhaps one can already do that with Merkle tree inclusion and consistency proofs. Definitely good times ahead for doing cryptography.

You could crop the picture and the result would no longer be singed. However, if someone wanted proof that the cropped picture is genuine, you could offer the uncropped signed version and do a pixel by pixel comparison of the cropped area. Kind of like a chain of provenance to a signed source.

This could work for other manipulation. Change the colors in the image. Then if someone wants proof, offer the original and describe the transformation.

Sure. But what if the cropped part is sensitive content? Or if the video is exceedingly long? Then, providing a full source could become prohibitive.

IIRC there was a post here a while ago about I think Canon or Nikon working on that. But unless there's a chain of trust or journalists upload RAW files, they'd basically be untrustable.

An initiative exists: https://en.wikipedia.org/wiki/Content_Authenticity_Initiativ...

But this is essentially the same problem statement as DRM: provide the user with some cryptographic material, yet limit how they can use it and prevent them from just dumping it. Logically, there will always be a hole. Practically, you can make it very annoying to do, beyond the ability of the average consumer [1], but someone will probably manage, and given the scenarios we often talk about (e.g. state-backed disinformation), there will be plenty of resources spent on doing that. The payoff will cover the cost

Paradoxically, one could argue that a "95% trustworthy" system could actually do net harm. The higher people's trust builds in it, the greater the fall damage if someone manages to secretly subvert it, and use it on just the right bit of disinfo at the right time (contrasting my footnote about DRM)

[1] Hence why claims that DRM is a complete failure miss the point a bit - it's not needed to stop everyone. Perhaps we can crack some given DRM system, but the fact that you even have to download a new program is enough to stop a massive amount of consumers from bothering

Reply on news.ycombinator.com