LASTor: A Low-Latency AS-Aware Tor Client

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

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

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

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

Improve poor latency  Factors of causing latency Propagation delay Queuing delay Transmission delay

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

Effection on WSP  Shorter paths can greatly reduce latency  Path can not be derministic

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

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

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

Latency Comparison

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