Research On Security Analysis And Anonymity Enhancement Of Loopix Anonymous Communication System

Anonymous communication technology aims at secure communication over inse-cure channels to protect users’metadata.The prism incident has raised unprecedented concerns about privacy among Internet users.The fall of the Dark Web“Silk Road”has intensified doubts about the security of anonymous systems.Loopix,first proposed in2017,seeks to overcome the lack of security such as Tor network and build a new anony-mous communication infrastructure with high security and low latency.The Nym network based on Loopix has deployed a large number of volunteer nodes worldwide.However,there is currently a lack of in-depth research on Loopix’s security and vulnerability at home and abroad.The Loopix system is a new anonymous communication system based on the mes-sage architecture of mix-based technology.It mainly relies on cover traffic,Sphinx packet format and Poisson mixing strategy to achieve strong anonymity.This paper first builds the Loopix network experimental platform to test the system characteristics and analyzes the security of the Loopix system.On this basis,from the perspective of system anonymity enhancement,an experiment is designed to evaluate the contribution of loop messages generated by mixing nodes to the anonymity of system,and a non-cooperative adaptive adjustment scheme based on the loop messages send by the mixing nodes is proposed.The main work is as follows:（1）In view of the lack of research on the new Loopix anonymous communication system at home and abroad,this paper systematically summarizes seven attack modes.The security of Loopix system is analyzed,and the attack types that Loopix system can defend against are theoretically analyzed according to the seven types of attack modes.Combined with the characteristics of Loopix system,the vulnerability of Loopix system is found and two possible security threats are analyzed:intersection attack and denial of service attack.（2）In view of the lack of effective evaluation method for the contribution of Loopix system anonymity from the loop messages generated by mixing nodes,the anonymity evaluation indexεis firstly studied.Based on the construction of Loopix anonymous network experimental platform and system characteristics test,we point out the limitation ofεwhen evaluating the end-to-end anonymity by designed experiment and verify the influence of p₁（p₂）onε.Then combined with the control variable method to ensure the consistency of p₁（p₂）,the influence of loop messages generated by the mixing node on system anonymity was tested.The experimental results show that the anonymity gain of the loop message sent by mixing nodes is obvious,even stronger than that of the cover message sent by the clients.（3）In view of the lack of concrete and effective implementation scheme of the loop messages generated by the mixing nodes in the existing research papers,based on the anonymity measurement theory of continuous-timing model,combined with the require-ments of“minimum anonymity”guarantee,resistance to intersection attack and reduction of resource consumption,and considered the defense measures against n-1 attack.This paper proposes a non-cooperative adaptive adjustment scheme for the sending rate of loop messages generated by mixing nodes in Loopix system,which ensures the anonymity of the system and reduces the resource consumption of the system.Comparative experi-ments show that the non-cooperative adaptive adjustment algorithm achieves the desired effect.