Karsten Loesing

Performance Measurements and Statistics of Tor Hidden Services

Tor (the onion routing) provides a secure mechanism for offering TCP-based services while concealing the hidden servers IP address. In general the acceptance of services strongly relies on its QoS properties. For potential Tor users, provided the anonymity is secured, probably the most important QoS parameter is the time until they finally get response by such a hidden service. Internally, overall response times are constituted by several steps invisible for the user. We provide comprehensive measurements of all relevant latencies and a detailed statistical analysis with special focus on the overall response times. Thereby, we gain valuable insights that enable us to give certain statistical assertions and to suggest improvements in the hidden service protocol and its implementation.

Performance Measurements of Tor Hidden Services in Low-Bandwidth Access Networks

Being able to access and provide Internet services anonymously is an important mechanism to ensure freedom of speech in vast parts of the world. Offering location-hidden services on the Internet requires complex redirection protocols to obscure the locations and identities of communication partners. The anonymity system Tor supports such a protocol for providing and accessing TCP-based services anonymously. The complexity of the hidden service protocol results in significantly higher response times which is, however, a crucial barrier to user acceptance. This communication overhead becomes even more evident when using limited access networks like cellular phone networks. We provide comprehensive measurements and statistical analysis of the bootstrapping of client processes and different sub-steps of the Tor hidden service protocol under the influence of limited access networks. Thereby, we are able to identify bottlenecks for low-bandwidth access networks and to suggest improvements regarding these networks.

Implementation of an Instant Messaging System with Focus on Protection of User Presence

Instant messaging (IM) systems provide its users with the information of which of their contacts are currently online. This presence information supplements text communication of IM systems and is an additional value compared to other synchronous communication media. Unauthorized users could illegally generate online logs of users by exploiting their presence information. Public IM systems lack the reliable means to protect user presence and force the user to trust in the central registry server. In this paper, we propose an IM system, which is explicitly designed to protect user presence without the need of a trusted central registry. We present a Java implementation based on the anonymous communication network Tor [1], the cryptographic suite Bouncy Castle [2], and the distributed hash table OpenDHT [3].

An implementation of reliable group communication based on the peer-to-peer network JXTA

Summary form only given. In this paper we propose a new peer-to-peer protocol for atomic reliable multicast based on view consistency. It is designed for nearly real-time collaborative applications which require consistency of data in a group of participants. A typical example for this is drawing on a shared whiteboard. Collaborations frequently arise in an ad-hoc way in which setting up and operating a dedicated server is not feasible. Thus, our protocol is intended to be used in server-less environments and avoids dependence on central components. We implemented our protocol using the peer-to-peer middleware JXTA for use in TCP/IP-connected networks. This implementation offers its service to other applications via a lean Java API.