268 research outputs found
MeritRank: Sybil Tolerant Reputation for Merit-based Tokenomics
No full textDecentralized reputation schemes present a promising area of experimentation in blockchain applications. These solutions aim to overcome the shortcomings of simple monetary incentive mechanisms of naive tokenomics. However, there is a significant research gap regarding the limitations and benefits of such solutions. We formulate these trade-offs as a conjecture on the irreconcilability of three desirable properties of the reputation system in this context. Such a system can not be simultaneously generalizable, trustless, and Sybil resistant. To handle the limitations of this trilemma, we propose MeritRank: Sybil tolerant feedback aggregation mechanism for reputation. Instead of preventing Sybil attacks, our approach successfully bounds the benefits of these attacks. Using a dataset of participants’ interactions in MakerDAO, we run experiments to demonstrate Sybil tolerance of MeritRank. Decay parameters of reputation in MeritRank: transitivity decay and connectivity decay, allow for a fine-tuning of desirable levels of reputation utility and Sybil tolerance in different use contexts.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Data-Intensive System
Achieving Sybil-Proofness in DistributedWork Systems
No full textIn a multi-agent system where agents provide quantifiable work for each other on a voluntary basis, reputation mechanisms are incorporated to induce cooperation. Hereby agents assign their peers numerical scores based on their reported transaction histories. In such systems, adversaries can launch an attack by creating fake identities called Sybils, who report counterfeit transactions among one another, with the aim of increasing their own scores in the eyes of others. This paper provides new results about the Sybil-proofness of reputation mechanisms. We revisit the impossibility result of Seuken and Parkes (2011), who show that strongly-beneficial Sybil attacks cannot be prevented on reputation mechanisms satisfying three particular requirements. We prove that, under a more rigorous set of definitions of Sybil attack benefit, this result no longer holds. We characterise properties under which reputation mechanisms are susceptible to strongly-beneficial Sybil attacks. Building on our results, we propose a minimal set of requirements for reputation mechanisms to achieve resistance to such attacks, which are stronger than the results by Cheng and Friedman (2005), who show Sybil-proofness of certain asymmetric reputation mechanisms.Dataintensive SystemsDiscrete Mathematics and Optimizatio
Towards Sybil Resilience in Decentralized Learning
No full textFederated learning is a privacy-enforcing machine learning technology but suffers from limited scalability. This limitation mostly originates from the internet connection and memory capacity of the central parameter server, and the complexity of the model aggregation function. Decentralized learning has recently been emerging as a promising alternative to federated learning. This novel technology eliminates the need for a central parameter server by decentralizing the model aggregation across all participating nodes. Numerous studies have been conducted on improving the resilience of federated learning against poisoning and Sybil attacks, whereas the resilience of decentralized learning remains largely unstudied. This research gap serves as the main motivator for this study, in which our objective is to improve the Sybil poisoning resilience of decentralized learning.We present SybilWall, an innovative algorithm focused on increasing the resilience of decentralized learning against targeted Sybil poisoning attacks. By combining a Sybil-resistant aggregation function based on similarity between Sybils with a novel probabilistic gossiping mechanism, we establish a new benchmark for scalable, Sybil-resilient decentralized learning.A comprehensive empirical evaluation demonstrated that SybilWall outperforms existing state-of-the-art solutions designed for federated learning scenarios and is the only algorithm to obtain consistent accuracy over a range of adversarial attack scenarios. We also found SybilWall to diminish the utility of creating many Sybils, as our evaluations demonstrate a higher success rate among adversaries employing fewer Sybils. Finally, we suggest a number of possible improvements to SybilWall and highlight promising future research directions.Computer Engineering | Distributed System
MarketPalace: A Sybil-Resistant and Decentralized Marketplace
No full textFraudulent behavior within online marketplaces is a prominent but unsolved problem. Most marketplace operators try to mitigate this behavior by serving as the central authority. This approach requires user data collection and is not privacy-friendly. In an attempt to build a foundation for solving the fraud concerns and privacy issues, this paper elaborates on the design and implementation of a simple marketplace system using peer-to-peer (P2P) technology in combination with a Self-Sovereign Identity (SSI) solution. The P2P network ensures no single points of control, reduces risks of a big data breach and simply costs less to operate. The SSI solution makes sure that users cannot create multiple accounts to whitewash their dishonest behavior. Ensuring every user has only one identity makes the platform Sybil-resistant. In contrast to other identity verification systems used in marketplaces, such as Facebook Login, SSI aims to put the user in control and to not collect personal data. Users know what data are asked and give explicit consent for each request. This user-centric approach makes them privacy-friendly. Reaching Sybil resistance without having a central authority in a marketplace has not been done before. In the future a reputation system can be built on top of the Sybil-resistant P2P system, ensuring users’ behavior can not be whitewashed. Several methods are used during the design and the implementation process. They include the Scrum framework, MoSCoW prioritization and Class-Responsibility-Collaboration cards. Git was used for version control while code quality was kept high through a custom CI setup. Additionaly, every merge request required at least two approvals to ensure thorough code review. This resulted in an application that is both Sybil-resistant and privacy-friendlyElectrical Engineerin
Web3 Sybil avoidance using network latency
No full textWeb3 is emerging as the new Internet-interaction model that facilitates direct collaboration between strangers without a need for prior trust between network participants and without central authorities. However, one of its shortcomings is the lack of a defense mechanism against the ability of a single user to generate a surplus of identities, known as the Sybil attack. Web3 has a Sybil attack problem because it uses peer sampling to establish connections between users. We evaluate the promising but under-explored direction of Sybil avoidance using network latency measurements, according to which two identities with equal latencies are suspected to be operated from the same node, and thus are likely Sybils. Network latency measurements have two desirable properties: they are only malleable by attackers by adding latency, and they do not require any trust between network participants. Our basic SybilSys mechanism avoids Sybil attackers using only network latency measurements if attackers do not actively exploit their malleability. We present an enhanced version of SybilSys that protects against targeted attacks using a variant of the flow correlation attack, which we name TrafficJamTrigger. We show how the message flows of Round-Trip Time measurements can be used to expose attack patterns and we propose and evaluate six classifiers to recognize these patterns. Our experiments show, through both emulation and real-world deployment, that enhanced SybilSys can serve a fundamental role for Web3, effectively establishing connections to real users even in the face of networks consisting of 99% Sybils
TrustChain: A Sybil-resistant scalable blockchain
No full textTrustChain is capable of creating trusted transactions among strangers without central control. This enables new areas of blockchain use with a focus on building trust between individuals. Our innovative approach offers scalability, openness and Sybil-resistance while replacing proof-of-work with a mechanism to establish the validity and integrity of transactions.TrustChain is a permission-less tamper-proof data structure for storing transaction records of agents. We create an immutable chain of temporally ordered interactions for each agent. It is inherently parallel and every agent creates his own genesis block. TrustChain includes a novel Sybil-resistant algorithm named NetFlow to determine trustworthiness of agents in an online community. NetFlow ensures that agents who take resources from the community also contribute back. We demonstrate that irrefutable historical transaction records offer security and seamless scalability, without requiring global consensus. Experimentation shows that the transaction throughput of TrustChain surpasses that of traditional blockchain architectures like Bitcoin. We show by using extracted data from a live network that TrustChain has sufficient informativeness to identify freeriders, leading to refusal of service.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Education and Research SupportData-Intensive System
Detecting Sybil Nodes in Static and Dynamic Networks
No full textabstract: Peer-to-peer systems are known to be vulnerable to the Sybil attack. The lack of a central authority allows a malicious user to create many fake identities (called Sybil nodes) pretending to be independent honest nodes. The goal of the malicious user is to influence the system on his/her behalf. In order to detect the Sybil nodes and prevent the attack, a reputation system is used for the nodes, built through observing its interactions with its peers. The construction makes every node a part of a distributed authority that keeps records on the reputation and behavior of the nodes. Records of interactions between nodes are broadcast by the interacting nodes and honest reporting proves to be a Nash Equilibrium for correct (non-Sybil) nodes. In this research is argued that in realistic communication schedule scenarios, simple graph-theoretic queries such as the computation of Strongly Connected Components and Densest Subgraphs, help in exposing those nodes most likely to be Sybil, which are then proved to be Sybil or not through a direct test executed by some peers.Dissertation/ThesisPh.D. Computer Science 201
Implication de l\u27apolipoprotéine AV dans le déterminisme des hyperchylomicronémies
No full textLe gène de l\u27apolipoprotéine (apo) AV, est un nouveau gène candidat pour étudier les mécanismes des hyperchylomicronémies, largement méconnus. Nous avons identifié, dans une cohorte de 286 patients ayant présenté une hyperchylomicronémie, indemnes de mutation sur la lipoprotéine lipase (LPL) ou l\u27apoCII, 3 mutations de l\u27APOA5 : Q139X et Q97X, et L242P. Nous présentons, à travers 2 études, la description phénotypique et génotypique des cas index et de leurs familles ainsi que la caractérisation fonctionnelle des mutations. Les mutations Q97X et Q139X ont été clairement impliquées dans l\u27hyperchylomicronémie à l\u27état homo ou hétéroygote, et associée à un défaut de lipolyse intravasculaire. L\u27expression phénotypique des mutations chez les hétérozygotes était très variable, influencée par des co-facteurs génétiques, en particulier les haplotypes variants de l\u27APOA5, et plus faiblement par l\u27environnement métabolique. Par ailleurs, nous avons montré, dans une 3ème étude, l\u27association des haplotypes variants de l\u27APOA5 et la survenue d\u27une hypertriglycéridémie modérée ou sévère dans une cohorte de patients diabétiques de type 2. Nos travaux ont permis de confirmer pour la première fois chez l\u27homme le lien fonctionnel entre l\u27apoAV et la lipoprotéine lipase (LPL). Nous proposons un nouveau modèle d\u27interaction entre ces deux protéines : l\u27apoAV régulerait la lipolyse intravasculaire par la LPL en agissant sur son expression à la surface de l\u27endothélium vasculaire
Stage and radio organist Sybil Chism.
No full textStage and radio organist Sybil Chism. From the back: "'Lovely Muscian' Sybil Chism is the organist of the NBC One Man's Family heard each Wednesday from 8:00 to 8:30 p.m., EST, over the NBC-Red Network. As pretty as her melodies, Miss chism attained fame as a pianist and theater organist before Carlton Morse, author of One Man's Family, selected her over leading Hollywood artists."To order a reproduction, inquire about permissions, or for information about prices see:
http://www.lib.washington.edu/specialcollections/services/reproduction/reproduction
Please cite the Order NumberScanned at 600ppi with an Epson 20000 flatbed scanner. Image then rotated, cropped, level-adjusted, and sharpened using Photoshop CS3. Converted to a JPEG2000 image upon ingest into CONTENTdm
Disraeli's Political Philosphy as Expressed Through Coningsby and Sybil
No full textiii, 65 p.Coningsby and Sybil are not only works of art, but
the manifesto of Young England, and as such, political documents.
It is with these two novels that this paper will
deal, not as works of art, but as vehicles to a Greater
understanding of the political philosophy of the author, Benjamin
Disraeli
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