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Comment by noman-land | Hacker News Reader

There are a few that I've thought about but the first one that comes to mind is proving you're 21+ to an alcohol store cashier without handing over your ID with all your personal info. You could just give them a ZK proof that returns a true/false and they could check it against encrypted data (signed by the DMV).

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Why is that preferable over a message attesting “over 21” signed by the DMV?

The hard parts here are retrofitting society to use a digital ID and how to prove that the human in front of you is attached to that digital ID.

The solutions there all seem like dystopias where now instead of a bouncer looking at your ID for a few seconds, technology is taking pictures of you everywhere and can log that with location and time trivially.

It doesn't have to be a digital ID, it can just be encrypted data encoded on a regular ID on a QR code.

Age depends on timestamp. The encrypted data is stored on the ID and signed by the DMV, with a function that can be run by the bouncer's scanning machine that plugs in a now() timestamp, and receives a boolean in return. The DMV doesn't even need to be involved after the issuance of the ID and no network access is needed for this calculation.

No one's location was tracked and no one's picture was taken and now a bouncer who fancies you can't turn up at your house after glancing at your ID.

Age verification (without leaking other PII) was the illustrative scenario for W3C Verified Credentials (it lets you use a validating authority to sign specific subset of your schema).

There’s lots of other ways to solve the problem for verification/signing use cases tbh. Homomorphic encryption shines best when you are looking at more complex calculations than just a Boolean result - such as tax calculations.

Can you submit your financial information and have your taxes calculated without revealing the amounts involved? Can you apply filters to an image without having the image readable by the server? It essentially allows us to “trust a remote server” in scenarios where one wouldn’t usually.

Still doesn’t quite justify homomorphic encryption if the computations involved are mundane (like tax calculations). The true use case is when the computation itself is proprietary, so that users don’t want to reveal their data but the provider also doesn’t want to divulge their algorithm. This is why ML models or finely tuned search engines are the examples most commonly cited, but of course those are also far outside the scale that could be achieved.

How do you know that the bouncers scanning machine didn’t log the interaction?

The whole value prop is built on not trusting that bouncer and by extension their hardware.

Everything would have to be encrypted leading to the bouncer also needing to establish that this opaque identifier actually belongs to you. This is where some picture or biometric comes into play and since the bouncer cannot evaluate it with their own wetware you are surrendering more data to a device you cannot trust.

They also cannot trust your device. So, I don’t see a scenario where you can prove ownership of the ID to a person without their device convincing them of it.

> No one's location was tracked and no one's picture was taken

I assume you mean the bouncer didn't take a photo, they just looked at the DMV photo embedded in the ID and did a visual comparison in their meat brain.

If there's no photo anywhere, how does the bouncer know I'm not using someone else's ID?

It's not. And since it is also 10000x slower than merely checking a signed number, nobody is interested in doing this.

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