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.
We introduce Torsk, a structured peer-to-peer low-latency anonymity protocol. Torsk is designed as an interoperable replacement for the relay selection and directory service of the popular Tor anonymity network, that decreases the bandwidth cost of relay selection and maintenance from quadratic to quasilinear while introducing no new attacks on the anonymity provided by Tor, and no additional delay to connections made via Tor. The resulting bandwidth savings make a modest-sized Torsk network significantly cheaper to operate, and allows low-bandwidth clients to join the network. Unlike previous proposals for P2P anonymity schemes, Torsk does not require all users to relay traffic for others. Torsk utilizes a combination of two P2P lookup mechanisms with complementary strengths in order to avoid attacks on the confidentiality and integrity of lookups. We show by analysis that previously known attacks on P2P anonymity schemes do not apply to Torsk, and report on experiments conducted with a 336-node wide-area deployment of Torsk, demonstrating its efficiency and feasibility.  We introduce a novel model of routing security that incorporates the ordinarily overlooked variations in trust that users have for different parts of the network. We focus on anonymous communication, and in particular onion routing, although we expect the approach to apply more broadly. This paper provides two main contributions. First, we present a novel model to consider the various security concerns for route selection in anonymity networks when users vary their trust over parts of the network. Second, to show the usefulness of our model, we present as an example a new algorithm to select paths in onion routing. We analyze its effectiveness against deanonymization and other information leaks, and particularly how it fares in our model versus existing algorithms, which do not consider trust. In contrast to those, we find that our trust-based routing strategy can protect anonymity against an adversary capable of attacking a significant fraction of the network. Network information distribution is a fundamental service for any anonymization network. Even though anonymization and information distribution about the network are two orthogonal issues, the design of the distribution service has a direct impact on the anonymization. Requiring each node to know about all other nodes in the network (as in Tor and AN.ON -- the most popular anonymization networks) limits scalability and offers a playground for intersection attacks. The distributed designs existing so far fail to meet security requirements and have therefore not been accepted in real networks. In this paper, we combine probabilistic analysis and simulation to explore DHT-based approaches for distributing network information in anonymization networks. Based on our findings we introduce NISAN, a novel approach that tries to scalably overcome known security problems. It allows for selecting nodes uniformly at random from the full set of all available peers, while each of the nodes has only limited knowledge about the network. We show that our scheme has properties similar to a centralized directory in terms of preventing malicious nodes from biasing the path selection. This is done, however, without requiring to trust any third party. At the same time our approach provides high scalability and adequate performance. Additionally, we analyze different design choices and come up with diverse proposals depending on the attacker model. The proposed combination of security, scalability, and simplicity, to the best of our knowledge, is not available in any other existing network information distribution system. The ability to locate random relays is a key challenge for peer-to-peer (P2P) anonymous communication systems. Earlier attempts like Salsa and AP3 used distributes hash table lookups to locate relays, but the lack of anonymity in their lookup mechanisms enables an adversary to infer the path structure and compromise used anonymity. NISAN and Torsk are state-of-the-art systems for P2P anonymous communication. Their designs include mechanisms that are specifically tailored to mitigate information leak attacks. NISAN proposes to add anonymity into the lookup mechanism itself, while Torsk proposes the use of secret buddy nodes to anonymize the lookup initiator. In this paper, we attack the key mechanisms that hide the relationship between a lookup initiator and its selected relays in NISAN and Torsk. We present passive attacks on the NISAN lookup and show that it is not as anonymous as previously thought. We analyze three circuit construction mechanisms for anonymous communication using the NISAN lookup, and show that the information leaks in the NISAN lookup lead to a significant reduction in user anonymity. We also propose active attacks on Torsk that defeat its secret buddy mechanism and consequently compromise user anonymity. Our results are backed up by probabilistic modeling and extensive simulations. Our study motivates the search for a DHT lookup mechanism that is both secure and anonymous. We consider using trust information to improve the anonymity provided by onion-routing networks. In particular, we introduce a model of trust in network nodes and use it to design path-selection strategies that minimize the probability that the adversary can successfully control the entrance to and exit from the network. This minimizes the chance that the adversary can observe and correlate patterns in the data flowing over the path and thereby deanonymize the user. We first describe the general case in which onion routers can be assigned arbitrary levels of trust. Selecting a strategy can be formulated in a straightforward way as a linear program, but it is exponential in size. We thus analyze a natural simplification of path selection for this case. More importantly, however, when choosing routes in practice, only a very coarse assessment of trust in specific onion routers is likely to be feasible. Therefore, we focus next on the special case in which there are only two trust levels. For this more practical case we identify three optimal route-selection strategies such that at least one is optimal, depending on the trust levels of the two classes, their size, and the reach of the adversary. This can yield practical input into routing decisions. We set out the relevant parameters and choices for making such decisions.