A Multi-path Tor Routing Algorithm Based On Composite Metrics

The Second Generation Onion Router(Tor),as the most popular anonymous communication system,has a huge user base.Tor’s initial design purpose is to provide anonymous services with low latency and reasonable throughput for interactive applications such as web browsing and instant messaging.The routing algorithm in Tor has a direct impact on these interactive users,including the anonymity and transmission performance provided to users.This thesis explains the workflow of Tor’s anonymous communication service and analyzes the potential shortcomings of Tor’s routing algorithm: the default routing algorithm may result in high latency due to circuitous link,high network node idle rate,and bulk traffic pre-empt bandwidth resources for interactive traffic.The following work has been carried out to solve the above problems.To solve the problem that the default routing algorithm of Tor may construct circuitous link,resulting in high propagation delay and lack of effective congestion control,this thesis proposes a path selection algorithm CM-Tor(Composite Metric).This algorithm will re-calculate the weight of nodes based on their geographic location and bandwidth information when selecting nodes in the link,which can avoid circuitous link.At the same time,based on the proposed delay estimation model,the RTT of the link is estimated in advance,and then the measured RTT of the link is obtained through the control unit when building the link,and the two are compared to determine whether the pre-built link is congested and whether it should be eliminated.To solve the problem of high idle node rate and bulk traffic pre-empting bandwidth resources for interactive traffic in the Tor network,this thesis proposes a multi-path transmission scheme based on composite metrics(CMM-Tor).CMM-Tor combines multiple links into a tunnel for transmitting bulk traffic.The selection of a single path in the scheme is based on CM-Tor,and the calculation method of node weight is modified to make the links in the tunnel preferentially use nodes with low bandwidth(which are generally idle).The aim is to isolate interactive traffic from bulk traffic and improve the resource utilization of the Tor network.This thesis conducts simulation tests of the improved Tor on the Shadow platform.The results show that,in highly congested network environments,CM-Tor loses 12% of anonymity compared to Tor,but reduces the time to first-byte by 14.7% and the download duration of 10 Mi B traffic by 15.0%.The simulation results also show that the CMMTor algorithm based on CM-Tor can reduce the latency of interactive traffic.In highly congested network environments,using CMM-Tor for bulk traffic can reduce the time to first-byte of interactive applications by 13.2% compared to Tor and improve the user experience of the Tor network.