Privacy Pass - Reducing CAPTCHAs for Tor users

Speaker/Bio

Sarah Scheffler is a PhD student studying applied cryptography in the computer science department working with Dr. Mayank Varia.

Abstract

Content Distribution Networks (CDNs) show CAPTCHAs when the user's IP address has low reputation. Tor exit nodes tend to have especially low IP reputation, so benevolent Tor users often see CAPTCHAs on every page they visit. Privacy Pass is a cryptographic protocol used by Cloudflare to grant tokens to Tor users that let them bypass CAPTCHAs while still preserving Tor's anonymity properties, using a Verifiable Oblivious Pseudorandom Function.