Optimizing Anonymity and Efficiency: A Critical Review of Path Selection Strategies in Tor

TL;DR

This paper evaluates five path selection strategies in Tor through high-fidelity simulations, revealing that geographic and congestion-aware methods improve latency and throughput, guiding future optimization of Tor's performance and anonymity balance.

Contribution

It provides a comprehensive comparative analysis of multiple path selection strategies in Tor, highlighting their strengths and limitations across different network scales.

Findings

Geographic (Latency-Optimized) strategy achieves lowest latency (40 ms).

Congestion-Aware strategy improves throughput by up to 42%.

No single strategy is optimal for all scenarios.

Abstract

The Onion Router (Tor) relies on path selection algorithms to balance performance and anonymity by determining how traffic flows through its relay network. As Tor scales and usage patterns evolve, default strategies such as bandwidth-weighted random selection and persistent guard nodes face increasing performance limitations. This study presents a comparative evaluation of five path selection strategies: Random, Guard, Congestion-Aware, and two Geographic approaches (Diversity Driven and Latency-Optimized) using a high-fidelity simulation model inspired by TorPS (Tor Path Simulator). Experiments were conducted across five network scales, simulating 37,500 circuits under realistic relay conditions. Results show that Geographic (Latency-Optimized) consistently achieved the lowest latency (40.0 ms) and highest efficiency, while Congestion-Aware strategies delivered the best throughput, outperforming the baseline by up to 42%. Guard nodes maintained stable routing but exhibited latency increases under larger networks. No single method proved optimal across all scenarios, but each revealed clear strengths for specific use cases. These findings demonstrate that targeted path selection can significantly improve Tor's performance without compromising anonymity, providing guidance for optimizing circuit construction in future development and deployments.