Research On The Availability Technique Of Anonymous Communication System

The rapid development of the Internet has made sharing information among all the people within a society a reality. And information security and privacy are gaining increasing attention. Confidentiality of user data is made possible in practice by the techniques of modern cryptography. Anonymity systems seek build an infrastructure running on top of the existing Internet pro-tocols which allows people to communicate with each other without revealing their personal network identities, so the attacker cannot learn who is commu-nicating with whom. Anonymity has been an essential requirement of many network applications. This thesis focuses on the problem of how to improve the availability and reachability of anonymity system under network censor-ship, the main contributions are listed as follows:·A general model of central resource distribution is proposed by study-ing the design of existing anonymity system and publishing the access-point resources with central-controlled discovery authority. Based on this model, mathematical and experimental analysis of its specialized model with random-choice strategy is given in two scenarios. In the case of non-confrontation, the relationship between the probability of all resources enumerated and the amount of attacker's enumeration. The result shows that the resource distribution service should select the appropriate amount of access points for each user and have a large number of active access points to improve the ability. In the case of confrontation, methods to measure the quality of resource distribution service and analysis of the two distribution strategies are given. Mechanisms for testing whether bridges are available, renewal speed of resources and the number of users attacker monitors and impersonates are important factors to the quality of the ser- vice.·According to the characteristics of distributing the resources through the social network where links reflects real-world social relationships among users, a resource distribution model is proposed. We analyze this model on the'small-world'network by numerical simulation. In the case of non-confrontation, attacker will discover all resources finally. In the case of confrontation, without renewal of resources, a small amount of avail-able resources still remains for some user on the network when there is no resources distribution between users. With renewal mechanism of re-sources, the confrontation also has a steady state. We find that the small world structure stands out as an efficient architecture for resource distri-bution service in scope of resource dissemination, proportion of available resources and average lifetime. And the attacker should use appropriate strategies to counter.·Existing anonymity systems are facing the problem that deploying a large number of access points requires significant investment to build resources or necessary incentives to attract more volunteers. We propose a system builds on existing overlay network, called SkyF2F. SkyF2F is a plug-in for Skype client that allows a user to establish a covert communication channel with her friends. We describe the design, a prototype implemen-tation and security analysis of SkyF2F. SkyF2F can successfully circum-vent several sophisticated censoring techniques. In addition, SkyF2F is easy to use, low cost, low latency. SkyF2F is very flexible. For example, it could be used as the access points to existing anonymous communica-tion systems. The idea of SkyF2F can also be adapted to other popular IM overlays.