The problem Cazk solves

Via the protocol, user can create proofs of inclusion or exclusion, which allows them to hide more information whilst asserting to be part of some group. The ability to prove exclusion is especially useful as it allows assertion such as "I am not part of this group and do not satisfy this set of conditions" whilst not revealing exactly what group or what properties the prover has when proving.

Challenges we ran into

There was a lot of trouble trying to get the circuits working! It may have been working via CLI, but so far there's no luck in a short notice to get circom to work for sparse merkle trees and getting the verifier contract up. The libraries provided for zk related seems to work fine by itself but when it comes to working together, there's some inconsistency between implementations.