Programming Zero Knowledge Proofs: From Zero to Hero

Imagine you are Goldman Sachs and a client wants to make a 100mm USD wire transfer to one of their accounts at Citibank. How does citibank know that the account at GS has the money to cover this transfer?

Right now, the way this works is essentially through a lot of trust and some guarantees by the fed. This has some downsides: because you need a lot of confirmations, it makes transfers take longer. Also, small players can't really get in on this system, so some regional banks are at a disadvantage.

How do you make this safer and more robust? GS obviously can't send info on all of its clients accounts and balances to Citi. You could imagine a protocol where the client/GS sends Citi a zkp to prove that the client has the money (as long as all inputs are agreed upon).

Of course, you don't really need zkps. You could also have the fed keep a database on all money in all accounts (like they do in Brazil), so that the bank only has to ask the central bank to give you an ok. But that is a whole lot of power in the hands of a central authority, as well as a single point of failure, which is something banking systems should avoid imo

The most common example in the talks I've been to have been for verifying anonymous voting amongst a group that you want to verify is valid to vote in the process. ZKPs allow for doing this without needing a central authority to attest to the person's credentials.

But it is early days and I think there's going to be many more use cases in the future around data privacy. Take an example of credit bureaus. What if instead of a lender sending over all the personally identifiable information needed to do a lookup it could instead send a ZKP to prove it knows enough information about an individual to be authorized to retrieve their record, meaning instead of sending SSN, DOB, Address, Phone, Name, they could instead just send enough specific values in the hash of a combo of some of those fields to prove that the full hash is known but without exposing the full hash itself (along with the existing shared secret to have authorization do lookup a value in the credit bureau in the first place).

This is a great explainer from one of the pioneers in this space, in case you weren't already familiar with it: https://www.wired.com/video/watch/5-levels-zero-knowledge-pr...

Are there any real uses of ZKP outside of blockcrap?

> without disclosing the actual birthdate

What prevents the birthdate from being gleaned through a simple binary search? Or, if it's specifically an "over 18 today?" query based on some decentralized timestamp source, what prevents the query from just being repeated every day until the result changes (assuming it returns "under 18" at first)?