PRIVACYPASS

Privacy Pass interacts with supporting websites to introduce an anonymous user-authentication mechanism. In particular, Privacy Pass is suitable for cases where a user is required to complete some proof-of-work (e.g. solving an internet challenge) to authenticate to a service. In short, the extension receives blindly signed ‘passes' for each authentication and these passes can be used to bypass future challenge solutions using an anonymous redemption procedure. For example, Privacy Pass is supported by Cloudflare to enable users to redeem passes instead of having to solve CAPTCHAs to visit Cloudflare-protected websites... We have written a paper that has been accepted into the 2018 edition of the Privacy Enhancing Technologies Symposium (PETS2018). In the paper, we formalize the protocol and are able prove (based on discrete-log-based cryptographic assumptions) some of the security properties that we require for guaranteeing anonymity and unforgeability. We also provide more details..