XRD: Scalable Messaging System with Cryptographic Privacy
summary
XRD (Crossroads) is a deployed-style messaging design that uses many parallel mix networks and a new primitive aggregate hybrid shuffle to make verifiable shuffles practical; proof costs drop to n+2 exponentiations for provers and four for verifiers. With 100 servers it handles 2 million users in ~228 seconds, resists active attacks via lightweight zero-knowledge checks, and in experiments is multiple× faster than prior cryptographic systems (Atom, Pung) while keeping cryptographic metadata privacy.
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chapters (13)
- 0:00Intro
- 0:25Motivation: whistleblowing
- 2:03Metadata private messaging system
- 2:56Deployment and threat model
- 5:13XRD: Overview
- 10:16Problem: Active attack
- 11:18Solution: Zero-knowledge proofs
- 12:52Chain selection
- 13:54Scalability properties
- 15:12Implementation and setup
- 16:10Latency increases linearly with the number of users
- 17:32XRD scales with more servers
- 18:52Summary of XRD • Cryptographic metadata privacy + scalability
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