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Privacy Pass

Privacy Pass

Privacy Pass helps to make solving CAPTCHAs online less painful using zero-knowledge cryptography. This project was done 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 an amount of unlinkable tokens in exchange for solving a CAPTCHA challenge. Users can redeem tokens in the future for accessing to services without having to interact with a challenge, and the service cannot link the redeemed token to previously-issued tokens.

Launched in 2017, Privacy Pass is available in the form of a browser extension, and since then, it is in use by over a hundred thousand monthly active users in Chrome and Firefox.


2022A Fast and Simple Partially Oblivious PRF, with Applications

Advances in Cryptology – EUROCRYPT 2022: 41st Annual International Conference on the Theory and Applications of Cryptographic Techniques, Trondheim, Norway, May 30 – June 3, pp. 674–705, 2022.
Nirvan Tyagi, Sofía Celi, Thomas Ristenpart, Nick Sullivan, Stefano Tessaro, Christopher A. Wood

2018Privacy Pass: Bypassing Internet Challenges Anonymously

Proceedings on Privacy Enhancing Technologies, no. 3 (2018), pp. 164-180. 2018.
Alex Davidson, Ian Goldberg, Nick Sullivan, George Tankersley, Filippo Valsorda

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