Dissertation Defense

Non-Hierarchical Networks for Censorship-Resistant Personal Communication

David R. Bild

The Internet promises widespread access to the world's collective information
and fast communication among people, but common government censorship and
spying undermines this potential. This censorship is facilitated by the Internet's
hierarchical structure. Most traffic flows routers owned by a small number of
ISPs, who can be secretly coerced into aiding such efforts. Traditional defenses
use cryptographic means to provide security and anonymity at the cost of key
management schemes that are confusing to common users. This thesis instead
advocates non-hierarchical networks that lack such chokepoints, instead requiring
would-be censors to control a substantial fraction of the participating devices"”an
expensive proposition.
We take four steps towards the development of practical non-hierarchical networks.
(1) We first describe Whisper, a non-hierarchical mobile ad hoc network
(MANET) architecture for personal communication among friends and family that
resists censorship and surveillance. At its core are two novel techniques, an efficient
routing scheme based on the predictability of human locations and a variant
of onion-routing suitable for decentralized MANETs. (2) We describe the design
and implementation of Shout, a MANET architecture for censorship-resistant,
Twitter-like public microblogging. (3) We describe the Mason test, a method to
detect Sybil attacks in ad hoc networks in which trusted authorities are not available
and used by Whisper. (5) We characterize and model the aggregate behavior
of Twitter users to enable simulation-based studied of systems like Shout. We use
our characterization of the retweet graph also study the retweet graph to analyze a
novel spammer detection technique for Shout.

Sponsored by

Robert Dick