  Anonymity networks hide user identities with the help of relayed anonymity
routers. However, the state-of-the-art anonymity networks do not provide an
effective trust model. As a result, users cannot circumvent malicious or
vulnerable routers, thus making them susceptible to malicious router based
attacks (e.g., correlation attacks). In this paper, we propose a novel social
network based trust model to help anonymity networks circumvent malicious
routers and obtain secure anonymity. In particular, we design an input
independent fuzzy model to determine trust relationships between friends based
on qualitative and quantitative social attributes, both of which can be readily
obtained from existing social networks. Moreover, we design an algorithm for
propagating trust over an anonymity network. We integrate these two elements in
STor, a novel social network based Tor. We have implemented STor by modifying
the Tor's source code and conducted experiments on PlanetLab to evaluate the
effectiveness of STor. Both simulation and PlanetLab experiment results have
demonstrated that STor can achieve secure anonymity by establishing trust-based
circuits in a distributed way. Although the design of STor is based on Tor
network, the social network based trust model can be adopted by other anonymity
networks.
