PrivacyPass

Privacy Pass is a privacy-enhancing protocol and browser extension that enables users to authenticate to services without compromising their anonymity. The extension interacts with supporting websites to introduce a blind signing procedure, ensuring that passes redeemed in the future are not linkable to those signed. The protocol is based on Verifiable, Oblivious Pseudorandom Functions (VOPRFs) built from elliptic curves, guaranteeing privacy and anonymity for users. Key features include the ability to bypass internet challenges, anonymous redemption of passes, and a fast and secure protocol. The extension has undergone extensive testing and review, and is available for download. Use cases include bypassing CAPTCHAs on Cloudflare-protected websites, and the protocol has been standardized by the IETF. Technical implementation details include the use of elliptic curves, blind signing, and batch discrete logarithm equivalence proof. The extension is open-sourced under the BSD-3 license, and code contributions are welcome.