Any time I get someone to explain a real world use case they explain the concept of password hashing. Also, the only people who ever talk about "ZKPs" are these obviously non-technical crypto founders - it's possible they think it's a new thing when it's something we deal with everyday as developers.
I can't get anyone to explain how it's different than a password hash other than in these elaborate hypothetical scenarios that don't relate to technology.
Instead of asking your id police office pass you a circuit. You present your ID to the circuit and pass results to the officer. The officer then verifies you are not a criminal without ever looking at your documents.
This is the same fundamental thing as the password hash example. I can verify you without ever seeing your password, the policeman can verify you without ever seeing your documents - same exact concept.
My question is then: What is unique to ZKPs? Are the ZKP folks just asking us to start calling these techniques "ZKPs"?
When I use Clear for IDV is that a ZKP? Just like your example, they show the ID to Clear, but I never see the ID.
Hashing is a limited variant of ZKP which can answer one exact question. With ZKP you can also check if password has certain length, special characters, etc., without ever seen the password itself.
Clear is not ZKP because Clear servers learn all data from your documents. With ZKP Clear would only know that you hold an ID with details matching the ticket you also hold. This is just 1 bit of information instead of many.
Re: Hashing - The point of one-way encryption is that it can't be decrypted. A plaintext password has 1 job, to be read, not saved - yet you want to encrypt it as if it will be saved, but because it's one-way encrypted now it can't be read. What problem did you solve? You created a problem (that you now need ZKP to solve...)
Anyway, the ZKP concept is not about decrypting hashes at all, but looking at peripheral data to prove something (Alibaba Cave - Victor only knows Peggy knew the password because he had access to some other data - the path she took). "checking length etc." only if those hints are already available to the system in some way. And because of this approach, why would you need the hash? Just don't use passwords at all in the case of ZKP right? Simply rely on the other identifying data that you have access to, that you use anyway. Also - how secure is this loose profiling technique compared to email-backed passwords over HTTPS?
I imagine few product use cases allow for a server to trust all the clients with encryption, while not trusting itself - but there are some use cases like when the server is not the source of truth - file system service, or peer-to-peer stuff like ledgers: If the server's purpose is just to maintain a shared ledger and all the clients in the network are trusted.
But in the case we're talking about, of a service that authenticates clients, you're saying you can't trust the authenticator when that is kinda the point of authentication - they don't trust you, or rather - the server cannot tell for sure that any incoming connection is who they say they are, even if it has "zero knowledge" like their IP address and a face scan (your brother in the same house might pass). The point of a username and password is that you want the server to not trust any connecting clients unless they have this specific data precisely.
The ID would need to have some government digital signature for the ZK circuit to work. The proof would be "this digital ID that has this valid government signature shows XYZ".
The verifier would need the government public key and then can see "This ID that has been signed by the governments private key shows XYZ"
And the next question is: why bother? We have well-established protocols for the ID card: a police scanner creates a nonce and sends it to the card, the card signs it with its private key, and provides a certificate signed by the government.
The police scanner then verifies the signature and checks that the certificate is correctly signed by the government's public key.
They are useful from a mathematical point of view. (And explore the relationship between P and NP, for example.) Not sure if that counts as a 'real use' to you. See also https://en.wikipedia.org/wiki/PCP_theorem
At the moment, producing a zero knowledge proof has roughly a million-fold overhead compared to running a program directly. So there aren't many applications where that's acceptable. So I am very grateful that the blockchain people are more than happy to throw money at the math here. Very generous of them.
In principle, you can use ZKP for privacy preserving compliance work in real (ie traditional) finance.
> Eg Goldman Sachs could encode all their compliance rules in a program, and publish a proof that their books pass the check by that program, without revealing anything about their accounting.
> In a banking context, you could in theory also run your know-your-customer (KYC) rules against customer provided data, store the proof, and delete the original data. That way, you still have proof that your customers don't have ties to North Korea or Russia, but you can't be compelled by anyone to reveal the data later (nor accidentally leak that data, etc).
> Of course, for that latter application, you need a sharp lawyer to make sure that storing the proof instead of the original data is enough for your KYC obligations.
> If you want to go further, you could have your customers run the KYC rules locally, so that their data never leaves their premises.
> (For all these applications, you still have to have a mechanism that connects the real world to the inputs of the programs whose execution you are proving.
> So eg Goldman Sachs would still need an auditor that checks that the assets and obligations they have in their balance sheet actually exist, but the auditor does not otherwise need to make judgement calls or apply any rules.)
ZKPs have only become cheap and easy enough to do in the last few years, so of course Goldman Sachs doesn't use them yet. They'll be using them in a decade, for now look at startups. https://github.com/zk-passport/openpassport is one that is working today, worldcoin ID verification is another.
I carefully gave examples of where ZKP can be useful outside of blockchains.
> Like they don't use blockcrap for interbank settlements, asset tracking, notary, etc.
Yes. So far the only way to track real world assets on a blockchain is to have a trusted third party (or third parties) that connect whatever your blockchain says to the real world.
But if you have that trusted third party, you might as well have them run the database that keeps track of who owns what. No need for a blockchain.
ZKP is different in the sense that it's one of only a few things to come out of the 'crypto' world that has at least a _chance_ of being useful in the real world. One day. Perhaps.
(Cryptography in general is enormously useful. Have a look at HTTPS for one example. When I just say 'crypto' I mean specifically everything to do with the blockchain ecosystem. So far the only real applications of crypto / blockchains that I've seen are gambling (generously called 'speculation' or 'investment') and ransomware payments. Cryptocurrencies aren't even good for buying drugs on the black market so far.)
In any case, ZKP is still very immature. But we are very fortunate that the crypto-people are generously funding this area of essentially pure mathematics research.
This must be a mistake or misunderstanding, because "blockcrap" is hardly mentioned in contrast with examples like confirming someone is of age, meets certain insurance requirements or has certain financial status without revealing anything about them. No blockchain is needed in any of these examples.
Part of growing up means realizing that cryptocrap is cryptocrap.
> examples like confirming someone is of age
When where are the companies that do that? Can I replace my Washington driving license with a ZKP that I can show to police officers or to enter a pub?
There are really no practical examples of the actual usages. Just hand-waving. And moreover, all the examples you provided make no sense. They are far better achieved using classic asymmetric systems.
I can't get anyone to explain how it's different than a password hash other than in these elaborate hypothetical scenarios that don't relate to technology.