Many people have legitimate needs to avoid their online activities being tracked and linked to their real-world identities – from citizens of authoritarian regimes, to everyday victims of domestic abuse or law enforcement officers investigating organized crime. Current state-of-the-art anonymous communication systems are based on onion routing, an approach effective against localized adversaries with a limited ability to monitor or tamper with network traffic. In an environment of increasingly powerful and all-seeing state-level adversaries, however, onion routing is showing cracks, and may not offer reliable security for much longer. All current anonymity systems are vulnerable in varying degrees to five major classes of attacks: global passive traffic analysis, active attacks, “denial-of-security” or DoSec attacks, intersection attacks, and software exploits.
The Dissent project is developing a next-generation anonymity system representing a ground-up redesign of current approaches. Dissent is the first anonymous communication architecture incorporating systematic protection against the five major vulnerability classes above. By switching from onion routing to alternate anonymity primitives offering provable resistance to traffic analysis, Dissent makes anonymity possible even against an adversary who can monitor most, or all, network communication. A collective control plane ensures that a group of anonymous users behave indistinguishably even if an adversary interferes actively, such as by delaying messages or forcing users offline. Protocol-level accountability enables groups to identify and expel misbehaving nodes, preserving availability, and preventing adversaries from using denial-of-service attacks to weaken anonymity. The system computes anonymity metrics that give users realistic indicators of anonymity, even against adversaries capable of long-term intersection and statistical disclosure attacks, and gives users control over tradeoffs between anonymity loss and communication responsiveness. Finally, virtual machine insolation offers anonymity protection against browser software exploits of the kind recently employed to de-anonymize Tor users. While Dissent is still a proof-of-concept prototype with important functionality and performance limitations, preliminary evidence suggests that it may in principle be possible – though by no means easy – to hide in an Internet panopticon.