Scalable and Anonymity Preserving Overlays for Voice over IP Communications

Anonymous Voice over IP (VoIP) communication is an important tool to provide freedom of speech. For achieving a good trade-off between quality of service (QoS) and anonymity, connecting mixes by padded links is a promising approach. However, constructing suitable overlay topologies for establishing padded links is not easy: existing approaches are either not scalable with regard to the number of mixes because of using full meshes or impractical due to computational complexity of the algorithms used to create optimal reduced topologies. This prevents them from being deployed as volunteer-based networks like Tor. In this paper, we propose and study different heuristic strategies for reduced topology construction and path selection with low computational complexity. We evaluate our approach using latency and bandwidth estimations from the Tor network and demonstrate that we can achieve appropriate performance and anonymity metrics for VoIP. Especially, the achieved properties are similar to those of a recently proposed approach that calculates optimal topologies for small networks.