Hang With Your Buddies to Resist Intersection Attacks

TL;DR

Buddies is a novel system that enhances user anonymity in dynamic networks by grouping users into buddy sets, resisting intersection attacks while balancing privacy and communication responsiveness.

Contribution

It introduces a systematic design for intersection attack resistance that allows dynamic grouping and customizable attack mitigation policies in practical anonymity systems.

Findings

Buddies guarantees non-trivial anonymity sets in realistic scenarios.

The system effectively balances anonymity and responsiveness.

Prototype and simulations validate its practical effectiveness.

Abstract

Some anonymity schemes might in principle protect users from pervasive network surveillance - but only if all messages are independent and unlinkable. Users in practice often need pseudonymity - sending messages intentionally linkable to each other but not to the sender - but pseudonymity in dynamic networks exposes users to intersection attacks. We present Buddies, the first systematic design for intersection attack resistance in practical anonymity systems. Buddies groups users dynamically into buddy sets, controlling message transmission to make buddies within a set behaviorally indistinguishable under traffic analysis. To manage the inevitable tradeoffs between anonymity guarantees and communication responsiveness, Buddies enables users to select independent attack mitigation policies for each pseudonym. Using trace-based simulations and a working prototype, we find that Buddies can guarantee non-trivial anonymity set sizes in realistic chat/microblogging scenarios, for both short-lived and long-lived pseudonyms.