Shepherding the Tor network

Roger Dingledine, one of Tor's original developers, opens with the network's basics: volunteer relays, three-hop circuits, exit policies, and nine directory authorities that publish the hourly consensus. He explains why directory information was later moved onto relays so censors could not block the network by blocking a few addresses. He then ranks threats by how often they occur in practice, putting operational security mistakes first, followed by browser fingerprinting, browser exploits, traffic confirmation and traffic analysis.

The middle of the talk covers relay operators. The pool has shifted from home computers to university and nonprofit exit relays and then to cloud VPS providers, so a single host can end up carrying a large share of the network. Stories include an early abuse complaint triggered by a Windows installer, spoofed SSH scans that got directory authority addresses blocklisted, a botnet that briefly multiplied users, and a campaign of fake cryptocurrency exchange sites. The talk also covers legal and ethical questions around exit relays, content filtering, and the research safety board that reviews studies of users.

He closes with open problems: admission control that is less centralized, tracking how many relays the team personally knows, and routing that does not overload Europe. He urges the DEF CON audience to run relays and help build relay capacity in the United States.