Masoud Akhoondi Curtis Yu Harsha V. Madhyastha

1. LASTor: A Low-Latency AS-Aware Tor Client MasoudAkhoondiCurtis YuHarshaV. Madhyastha

2. Tor • Stands for The Onion Router • Goals: • Anonymity • Each hop only knows previous and next hop on a path • Low latency communication • 90% of Tor traffic is interactive

3. Problems on Tor • High latency in practice • Over 90% of connections in Tor network incurs latencies over 5x than on the direct Internet path. • Anonymity can break down • Path selection to establish a circuit in Tor is oblivious to Internet routing • Autonomous System(AS) correlate traffic cross entry and exit segments of a circuit

4. Potential Solution • Measure latencies and routes from each relay to all end-hosts • Choose a path with low latency and no common Ases on both entry and exit segment • However, none of them is deployed yet

5. LASTor • A low-latency AS-aware Tor client • Improve poor latency for interactive communications • Modify path selection to reduce latency • Prevent anonymity from breaking down • AS-aware path selection

6. Improve poor latency • Factors of causing latency • Propagation delay • Queuing delay • Transmission delay

7. Weighted Shortest Path • Based on the expected latency • Path with lower latency has high probability to be chosen • Clustering of relays

8. Effection on WSP • Shorter paths can greatly reduce latency • Path can not be derministic

9. Tunable Path Selection • User could balance anonymity and latency • Modified weight w to w(1-α) where 0 ≤α≤ 1

10. AS-aware Path Selection • Goal • Detect common Ases on entry and exit segments • Manner • AS set prediction algorithm

11. AS Set Prediction Algorithm • Modified version of Dijkstra’s algorithm • Predict ASes on all paths compliant with routing policies • Return a set of Ases on policy-compliant routes

12. Latency Comparison

13. Conclusion • LASTor client reduce latency and protect anonymity of Tor • LASTor can deliver a 25% reduction in median path latency