An empirical analysis of family in the Tor network

As one of the most popular anonymous communication systems, Tor has become a research hotspot in this area. Recently, Tor nodes from Tor families (referred to as family nodes) have played an increasingly important role and caused significant influence on the Tor network. However, existing research about Tor mostly focuses on the entire Tor network without much consideration about the difference between family nodes and the others. In order to analyze family nodes' contribution to the entire Tor network as well as their influence, this paper distinguishes family nodes from the others, and gives an empirical analysis of family nodes based on the live Tor network data of 3 years. Results show that, family nodes compose a small but full functional subset of Tor nodes; and compared with the other Tor nodes, they can provide relatively stable and high-performance service to Tor users. Furthermore, family nodes naturally form a hot area in the Tor network, relaying increasingly high-density traffic through a small number of nodes. Compared with random node targets, selective attacks focusing on family nodes can cause serious availability downgrade of the Tor network with much lower cost.