Privacy Pass

Launched in 2017 to help make solving CAPTCHAs online less painful using zero-knowledge cryptography in collaboration with researchers from Royal Holloway and the University of Waterloo. The core of Privacy Pass is a 1-RTT cryptographic protocol (based on an implementation of an oblivious pseudorandom function) that allows users to receive a significant amount of anonymous tokens in exchange for solving a challenge. These tokens can be exchanged in the future for access to services without having to interact with a challenge and without the service knowing which specific challenge was originally solved.

Privacy Pass is now in use by over a hundred thousand monthly active users in the form of the Privacy Pass browser extension for Chrome and Firefox.