MASOUD AKHOONDICURTIS YU

HARSHA V. MADHYASTHA

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 pathLow 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 downPath 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

communicationsModify path selection to reduce latency

Prevent anonymity from breaking downAS-aware path selection

Improve poor latency Factors of causing latency

Propagation delay Queuing delayTransmission 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

MannerAS 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