Hacker News Reader

Chain of custody is standard for evidence already. It might not be 100% infallible, but it certainly works better than nothing.

Yes, if a state actor wants to create evidence to frame you, and they didn't care about cost or returns, they could do so. But they could always do so. The fact is most of us are never going to get framed by a nation state.

The notion that you're either secure against all possible attacks or nothing is absurd.

Chain of custody implies you have some impartial authority who was actually there at the time to authenticate the recording. But then you would already have an impartial eyewitness. That doesn't work the other 99% of the time when the two parties to the case each tell a different story and one of them is offering evidence they have in their possession. The chain of custody then contains someone partial to the case and untrustworthy.

> Yes, if a state actor wants to create evidence to frame you, and they didn't care about cost or returns, they could do so. But they could always do so. The fact is most of us are never going to get framed by a nation state.

This is a major problem for elections. Nation states absolutely will doctor video of adversarial political candidates and for other propaganda purposes.

> The notion that you're either secure against all possible attacks or nothing is absurd.

But that's how signatures work. You're trusting every device in the world to sign the output of its camera. If the attacker can compromise any device, they can produce signed forgeries.

You're describing a situation where the recording ought not to be admissible anyways. If you can't trust where evidence came from, it's not evidence.

Again, nation states have always been able to doctor video of adversarial political candidates. Lookup pictures where the KGB made someone disappear.

Yes, if an attacker can compromise any device they can produce a signed forgery. But that's a really big if. There are a lot of potential attackers who can't compromise any and all devices, and signatures protect against them.

I guess the weakpoint in all of these techniques to prove a photo was taken by a certain device, at a certain time, in a certain place is for someone wearing a very good disguise to publicly commit crimes in your name. Any witnesses or photo evidence is going to point to you. A full movie costume makeup kit probably costs less than what it takes to hack Apple for someone's iPhone private key.

> The resources needed to forge a signature aren't going to be much different than the resources needed to create a deepfake to begin with.

How? If you have a public/private key pair and then do some kind of multisig process wherein the manufacturer can sign the photo, the OS can sign the photo, and then a user supplied signature could also sign the photo. You're not going to be able to fake 3 cryptographic signatures without 3 private keys. It would be extremely difficult to fake all of that. It would take a concerted, concentrated effort and would be extremely rare in practice. It would certainly improve the situation.

Once you compromise the device it doesn't matter how many keys there are because they all have to be on the device.

As a user, why does my private key need to be on the device? Especially, because I wouldn't want it there, because devices get stolen.

It has to be where the camera is. Otherwise the device holding your private key would need some way to authenticate photos from the device with the camera, which was the original problem.

First off, you'd have to steal the actual device. Then you'd have to break the device encryption itself to then extract a an encrypted version of a private key. (the private key itself can be encrypted with a password not stored on the device) You pair the 3 sigs plus a blockchain to track timestamps and photo hash signatures and maybe pair that with a different blockchain app to report lost or stolen devices...and you've got yourself as secure of a system as you can conceive in the age of deep fakes.

One threat is that a malicious actor uses a compromised device to fake a "legitimate" verified image.

This image can now be injected into the news cycle and be taken seriously.

Keeping a secret on the camera is more or less the "jailbreak problem", aka being able to make a dvd player or console that only does the things that the manufacturer wants.

I will be pretty sad if this problem is actually "solved" effectively because it portends a future where manufacturers can completely curtail user freedom. But...

If the key on the device is compromised by reverse engineering or because the manufacturer is compromised then the whole root of trust is gone.

Attackers can choose the weakest brand of camera.

You now have some doubt about any image that has been "verified" because it could have come from a compromised camera secret.

All the rest of the stuff, the blockchain, etc depends on the root of trust in the camera.

You also now have debates around camera country of origin because there is no near future world where governments can't lean on local manufacturers. Finally, doubt can be thrown on images retro-actively if we later learn that a camera we thought was secure, has vulnerabilities.

This isn't a "freedom" issue. And no, even if the private key on the device is hacked, you wouldn't be able to hack all the cameras (assuming the device manufacturer would embed a different key for each unit ID), you would still have to hack the OS and the User and the Phone's encryption. So the surface area of a hack would be small. You cannot fake all those signatures, you'd have to literally hack all that encryption.

All of this would be optional, of course. People can always edit out metadata. But it would lend credence and authority to a photograph or video. Which would carry more weight in a court of law, for example, where this stuff really matters.

This is an interesting conversation because we both seem convinced we're "obviously right". I am clearly having trouble understanding your point of view. I apologise in advance if I'm mis-understanding your argument. Perhaps "First off, you'd have to steal the actual device" from upthread is the clue.

I think the disconnect might be that you are working from a threat model where someone else is trying to tamper with an image from your camera. I agree you could make that arbitrarily difficult. But I am primarily concerned with the threat where someone is tampering with their own camera to fake evidence. This possibility makes it harder for you to prove that your own image is legitimate.

Your reasoning implies that one or two hacked cameras are not a problem. To my way of thinking, the possibility that "at least 1 hacked camera exists" or "any camera could possibly be hacked" are enough to throw doubt on any "verified" images that someone tries to present in a high stakes context such as national security or the courtroom. We're back to debating provenance.

I don't know. I don't want to live in a world where someone can literally murder someone on camera and get away with it on a technicality. Witness testimony is already used in court and is quite unverifiable and subject to all sorts of psychological phenomenon where people sometimes believe they saw something entirely different than what actually happened. I think cryptographic signatures couldn't guarantee validity 100%, but they could improve the situation in a world of deep fakes on demand.

It would require a larger degree of premeditation and effort to convincingly pull off a deep fake in that world.

> a technicality

It's not a technicality if the video can't be distinguished from perfect nonsense. Just as you don't let someone with a documented history of hallucinations testify on their own.

You'd make the camera reach out to a signing server for the user's signature. You'd even sign the whole photo, not a hash supplied by the camera, to give you (via the server) a chance to verify the image was correct.

Or, you'd adapt a hardware wallet to do the same. Either way, there'd be two devices from two manufacturers, communicating over a transparent protocol.

> The resources needed to forge a signature aren't going to be much different than the resources needed to create a deepfake to begin with

I imagine deepfakes will become way easier in the near future because there are legitimate commercial reasons to make them easy and accessible (for example digital art assets). I don't see the same happening for cracking devices, which is more a standard security cat and mouse game between hackers and device manufacturers.

All you're saying is that creating deepfakes would get easier, not that cracking devices would get harder. And it's already not hard enough to be a significant barrier.

One possibility would be for all recording devices to immediately upload checksums of their recorded footage to multiple trusted online authorities upon recording.

If someone presents altered footage, you can show that the checksum of the original was uploaded earlier.

This of course only covers certain cases. If the deepfake is crafted from scratch or from a camera that doesn't upload its checksums, and the incentive for the creation of the deepfake arises before the supposed time the deepfake takes place, then this method won't be of use.

Opt out and it's an invasion of privacy, opt in and nobody does and it isn't applicable to 99% of authentic footage.

And subject to attack. Don't want to be recorded? Jam wireless so they can't have anyone sign their videos, then claim they're fake.

Also doesn't work for state actors. A country can compromise three separate signing authorities.

I don't quite understand how it would be an invasion of privacy. All that's needed is a checksum paired with a timestamp, you don't even need to identify yourself. There is no way anyone could extract any meaningful information out of that without the footage.

And you can just upload it to ten different authorities in ten different jurisdictions, or even a hundred if you're paranoid. States are powerful but they're not _that_ powerful. It's the same principle that makes Tor work.

I agree jamming wireless could be an issue, but only for prosecution. In the case of proving innocence it's a moot point because this checksum system only covers after-the-fact fabrication anyway.

> you don't even need to identify yourself.

They'd also have logged the IP, which combined with a time will probably significantly narrow down the individual in question if you can also access telco records. Especially if inadvertently more information is also documented (such as a user agent).

> It's the same principle that makes Tor work.

Tor doesn't work for this kind of problem, unless you are significantly more technically savvy (and even then...) then the average smartphone user.

I think you missed the point regarding Tor. I mean that for Tor to be compromised, a state actor would need to compromise on the order of dozens to hundreds of nodes simultaneously. The fact that Tor works shows that they are unable to do this, and so they would also be unable to simultaneously compromise dozens of checksum authorities. Nothing to do with using Tor for uploading checksums, I was just using it as an example.

You’ve explained why it wouldn’t work flawlessly, but that doesn’t mean it wouldn’t work better than the current state of affairs. Video evidence is already useful in the legal system despite “video evidence” obviously not being a flawless system. A state actor or even a competent video effects studio with a modest budget could already create a convincing fake video!