Utilizing Public Blockchains for the Sybil-Resistant Bootstrapping of Distributed Anonymity Services

Distributed anonymity services, such as onion routing networks or cryptocurrency tumblers, promise privacy protection without trusted third parties. While the security of these services is often well-researched, security implications of their required bootstrapping processes are usually neglected: Users either jointly conduct the anonymization themselves, or they need to rely on a set of non-colluding privacy peers. However, the typically small number of privacy peers enable single adversaries to mimic distributed services. We thus present AnonBoot, a Sybil-resistant medium to securely bootstrap distributed anonymity services via public blockchains. AnonBoot enforces that peers periodically create a small proof of work to refresh their eligibility for providing secure anonymity services. A pseudo-random, locally replicable bootstrapping process using on-chain entropy then prevents biasing the election of eligible peers. Our evaluation using Bitcoin as AnonBoot's underlying blockchain shows its feasibility to maintain a trustworthy repository of 1000 peers with only a small storage footprint while supporting arbitrarily large user bases on top of most blockchains.Comment: To be published in the proceedings of the 15th ACM ASIA Conference on Computer and Communications Security (ACM ASIACCS'20

Decentralized Resource Availability Prediction in Peer-to-Peer Desktop Grids

Grid computing is a form of distributed computing which is used by an organiza­ tion to handle its long-running computational tasks. Volunteer computing (desktop grid) is a type of grid computing that uses idle CPU cycles donated voluntarily by users, to run its tasks. In a desktop grid model, the resources are not dedicated. The job (computational task) is submitted for execution in the resource only when the resource is idle. There is no guarantee that the job which has started to execute in a resource will complete its execution without any disruption from user activity (such as keyboard click or mouse move). This problem becomes more challenging in a Peer-to-Peer (P2P) model of desktop grids where there is no central server which takes the decision on whether to allocate a job to a resource. In this thesis we propose and implement a P2P desktop grid framework which does resource availability prediction. We try to improve the predictability of the system, by submitting the jobs on machines which have a higher probability of being available at a given time. We benchmark our framework and provide an analysis of our results

Geostry - a Peer-to-Peer System for Location-based Information

An interesting development is summarized by the notion of ”Ubiquitous Computing”: In this area, miniature systems are integrated into everyday objects making these objects ”smart” and able to communicate. Thereby, everyday objects can gather information about their state and their environment. By embedding this information into a model of the real world, which nowadays can be modeled very realistically using sophisticated 3D modeling techniques, it is possible to generate powerful digital world models. Not only can existing objects of the real world and their state be mapped into these world models, but additional information can be linked to these objects as well. The result is a symbiosis of the real world and digital information spaces. In this thesis, we present a system that allows for an easy access to this information. In contrast to existing solutions our approach is not based on a server-client architecture. Geostry bases on a peer-to-peer system and thus incorporates all the advantages, such as self-organization, fairness (in terms of costs), scalability and many more. Setting up the network is realized through a decentralized bootstrapping protocol based on an existing Internet service to provide robustness and availability. To selectively find geographic-related information Geostry supports spatial queries. They - among other things - enable the user to search for information e.g. in a certain district only. Sometimes, a certain piece of information raises particular interest. To cope with the run on the single computer that provides this specific information, Geostry offers dynamic replication mechanisms. Thereby, the information is replicated for as long as the rush lasts. Thus, Geostry offers all aspects from setting up a network, providing access to geo-related information and replication methods to provide accessibility in times of high loads

Content-Addressable Network for Distributed Simulations

The development of distributed systems, parallel computation technology, and Peer-to-Peer systems facilitates the realization of a distributed interactive world model. Thereby, we can implement a worldwide distributed simulation and virtual community, e.g., city traffic simulation and Massively Multiuser Virtual Environments (MMVE). In this thesis, we present Content-Addressable Network for Simulations (CANS), which is based on CAN. Thus, it incorporates all the advantages of CAN, such as self-organization, scalability, and fault-tolerance. The peers in CANS carry out the simulation for the zone assigned to them, and the zones are allocated in such a way that there is as little communication between the peers as possible. We propose two approaches for reorganizing zone-assignments after peers churn. These approaches are based on the distributed tree structure and prefix code. In comparison to existing approaches, our proposed approaches are more efficient and reliable. Since CANS is used to simulate “city traffic” and MMVE, it requires a low-dimensional key space, i.e., a two-dimensional or three-dimensional key space. Thus, we propose CAN tree routing and zone code routing, both of which adopt long links. CAN tree routing has a hierarchical design that is based on the CAN tree. Each peer equips two long links on average. Zone code routing is based on B*-tree. Each peer equips long links and shares the load evenly. Both of these routing solutions achieve routing hops on average. Consequently, the existing CAN can be optimized to perform simulations efficiently and reliably

Forschungsbericht Universität Mannheim 2006 / 2007

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