Research On Congestion Control Of The Second Genetation Onion Router

With the development of Internet,people are paying more and more attention on the protection of privacy.Anonymous communication system can effectively protect the privacy of Internet users.The second generation onion routing system Tor is the most widely used anonymous communication system.With the growing number of Tor users,the problem of congestion in Tor is attracting more and more attention.Tor's congestion problems hurt Tor's performance and Tor user's experience.In this paper,we first introduce Tor's basic theoretical,including Tor's network structure,circuit construction,data forwarding and circuit's queue structure.Then,based on Tor's online statistics and Tor's fundamentals,we summarize the causes of congestion.Based on the analysis of the causes,this paper classifies the Tor's congestion control solutions proposed by researchers in recent years,and introduces some typical congestion control solutions.Secondly,this paper proposes a circuit scheduling algorithm based on Weighted Round Robin(WRR).This paper describes the algorithm's design goals,the design and implementation of the algorithm,and the design of weight functions.Afterwards,this paper compares three kinds of weighting functions under different network congestion using Shadow,the simulator of Tor.And we choose the best performing weighting function under heavy network congestion.Then this paper introduces two circuit scheduling algorithms implemented in Tor,analyzes the shortcomings of these two algorithms,and simulates those circuit scheduling algorithms under different network congestion.By analyzing the simulation's results,it is verified that the WRR-based circuit scheduling algorithm can successfully mitigate the network congestion when the network is under heavy network congestion.Finally,this article analyzes the Sniper attack on IMUX.Firstly,this paper introduces the basic principles of IMUX and Sniper attacks.Subsequently,the paper describes the basic attack,efficient attack,and parallelizing attack on IMUX,and analyzes the attacker's bandwidth overhead and time overhead.Meanwhile,this paper introduces the defenses against Sniper attack,point out the influence of the serial number and timestamp of cell on the defense,and proposes the defense against the Sniper attack on IMUX.