Sophia: A local trust system to secure key-based routing in non-deterministic DHTs

Today, many distributed applications are typically deployed at a large scale, including Grid, web search engines and content distribution networks, and it is expected for their scale to grow more in terms of number of machines, locations and administrative domains. This poses many scalability issues related to the scale of the environment they run in. To explicitly address these issues, many distributed systems and everyday services use peer-to-peer (P2P) overlays to allow other parts of the system to benefit from the fault-tolerance and scalability of P2P technology. In particular, Distributed Hash Tables (DHTs), which implement a simple put-and-get interface to a dictionary-like data structure, have been extensively used to overcome the current limitations associated with the centralized and hierarchical components of distributed systems, including data management, resource discovery, job scheduling etc.However, DHTs exhibit a number of security problems in large-scale systems, where a large number of users are unknown to administrators (e.g., desktop grids). This makes the detection of malicious behavior an extremely complex task. As a result, attackers can disrupt the system in very dangerous ways, leading ultimately to the failure of the routing service, which is catastrophic for any DHT. To address this issue, we introduce Sophia, a new security technique which combines iterative routing with local trust to implement a secure lookup service with almost zero overhead. The key aspect to incur zero overhead is the use of local trust. In Sophia, each user identifies which routing entries are cooperative based on the success and failure of his own lookups, so no trust information is shared. Our simulation results demonstrate that Sophia does better than existing state-of-the-art solutions for secure routing in DHTs, both in stable and high dynamic environments, and even for collusive threat models.

► Secure lookup service for DHTs using local trust to allocate paths free of attackers.
► Exhaustive evaluation under several threat models and dynamic scenarios.
► Analysis of how the presence of whitewashers affects our lookup service.