Karsten Loesing

Learn More
The Tor network is one of the largest deployed anonymity networks, consisting of 1500+ volunteer-run relays and probably hundreds of thousands of clients connecting every day. Its large user-base has made it attractive for researchers to analyze usage of a real deployed anonymity network. The recent growth of the network has also led to performance(More)
Tor (the onion routing) provides a secure mechanism for offering TCP-based services while concealing the hidden server's 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(More)
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(More)
This paper proposes a protocol for decentralized service discovery with guarantees. We use a peer-to-peer network based on the distributed hashtable Chord that provides a structured overlay network in order to avoid flooding the whole network. Service descriptions are decomposed into portions which can be efficiently distributed and retrieved. We propose a(More)
Being a volunteer-run, distributed anonymity network, Tor is vulnerable to Sybil attacks. Little is known about real-world Sybils in the Tor network, and we lack practical tools and methods to expose Sybil attacks. In this work, we develop sybilhunter, the first system for detecting Sybil relays based on their appearance, such as configuration; and(More)
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(More)
Information about online presence allows participants of instant messaging (IM) systems to determine whether their prospective communication partners are able to answer their requests in a timely manner, or not. This makes IM more personal and closer than other forms of communication such as e-mail. On the other hand, revelation of presence constitutes a(More)
We propose a completely distributed peer-to-peer protocol for atomic reliable multicast based on view consistency. We implemented our protocol using the peerto-peer middleware JXTA for use in TCP/IP-connected networks. This implementation offers its service to other applications via a Java API. Typical applications are those requiring group communication(More)
The Tor network is periodically subject to Sybil attacks. Most of these attacks were not carefully executed and Tor directory authority operators were quick to detect and block the malignant relays. However, the Tor network lacks sophisticated tools to detect and protect against Sybil attacks. As a result, more advanced attacks could remain undetected.(More)
  • 1