13,131 research outputs found

    Phase-noise limitations in continuous-variable quantum key distribution with homodyne detection

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    In continuous-variables quantum key distribution with coherent states, the advantage of performing the detection by using standard telecoms components is counterbalanced by the lack of a stable phase reference in homodyne detection due to the complexity of optical phase-locking circuits and to the unavoidable phase noise of lasers, which introduces a degradation on the achievable secure key rate. Pilot-assisted phase-noise estimation and postdetection compensation techniques are used to implement a protocol with coherent states where a local laser is employed and it is not locked to the received signal, but a postdetection phase correction is applied. Here the reduction of the secure key rate determined by the laser phase noise, for both individual and collective attacks, is analytically evaluated and a scheme of pilot-assisted phase estimation proposed, outlining the tradeoff in the system design between phase noise and spectral efficiency. The optimal modulation variance as a function of the phase-noise amount is derived

    CryptoMaze: Atomic Off-Chain Payments in Payment Channel Network

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    Payment protocols developed to realize off-chain transactions in Payment channel network (PCN) assumes the underlying routing algorithm transfers the payment via a single path. However, a path may not have sufficient capacity to route a transaction. It is inevitable to split the payment across multiple paths. If we run independent instances of the protocol on each path, the execution may fail in some of the paths, leading to partial transfer of funds. A payer has to reattempt the entire process for the residual amount. We propose a secure and privacy-preserving payment protocol, CryptoMaze. Instead of independent paths, the funds are transferred from sender to receiver across several payment channels responsible for routing, in a breadth-first fashion. Payments are resolved faster at reduced setup cost, compared to existing state-of-the-art. Correlation among the partial payments is captured, guaranteeing atomicity. Further, two party ECDSA signature is used for establishing scriptless locks among parties involved in the payment. It reduces space overhead by leveraging on core Bitcoin scripts. We provide a formal model in the Universal Composability framework and state the privacy goals achieved by CryptoMaze. We compare the performance of our protocol with the existing single path based payment protocol, Multi-hop HTLC, applied iteratively on one path at a time on several instances. It is observed that CryptoMaze requires less communication overhead and low execution time, demonstrating efficiency and scalability.Comment: 30 pages, 9 figures, 1 tabl

    How to Incentivize Data-Driven Collaboration Among Competing Parties

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    The availability of vast amounts of data is changing how we can make medical discoveries, predict global market trends, save energy, and develop educational strategies. In some settings such as Genome Wide Association Studies or deep learning, sheer size of data seems critical. When data is held distributedly by many parties, they must share it to reap its full benefits. One obstacle to this revolution is the lack of willingness of different parties to share data, due to reasons such as loss of privacy or competitive edge. Cryptographic works address privacy aspects, but shed no light on individual parties' losses/gains when access to data carries tangible rewards. Even if it is clear that better overall conclusions can be drawn from collaboration, are individual collaborators better off by collaborating? Addressing this question is the topic of this paper. * We formalize a model of n-party collaboration for computing functions over private inputs in which participants receive their outputs in sequence, and the order depends on their private inputs. Each output "improves" on preceding outputs according to a score function. * We say a mechanism for collaboration achieves collaborative equilibrium if it ensures higher reward for all participants when collaborating (rather than working alone). We show that in general, computing a collaborative equilibrium is NP-complete, yet we design efficient algorithms to compute it in a range of natural model settings. Our collaboration mechanisms are in the standard model, and thus require a central trusted party; however, we show this assumption is unnecessary under standard cryptographic assumptions. We show how to implement the mechanisms in a decentralized way with new extensions of secure multiparty computation that impose order/timing constraints on output delivery to different players, as well as privacy and correctness

    Managing Development: EU and African Relations through the evolution of the Lomé and Cotonou Agreements

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    The relationship between the European Union 1 and Africa has been formalised since the beginning of the European integration project in the evolving Yaoundé, Lomé and now Cotonou Agreements. The relationship has shifted in line with the emerging global framework for neoliberal accumulation. This shift has involved the re-designing’ of developmental strategies and their ‘locking-in’ in the long term. Theoretically, this global shift in the organisation of both production and social relations (including popular understandings) has been well documented and the changing dominant patterns of production in advanced industrial economies has been highlighted at length. However, this article aims to develop further the idea of ‘locking-in’, outlined in the work of Stephen Gill, and to place an increased emphasis on the phenomena of both re-designing and locking-in as they apply to the alteration of developmental strategies in Less Developed Countries (LDCs), among which those in Africa have suffered from extreme marginalisation and exploitation. This article reveals the often ignored role of the EU in this process. It argues that the EU, through its institutionalised link with Africa, has played a key role in re-designing developmental strategies to complement the global shift to neoliberal accumulation which, in its latest phase, is aimed particularly at the complex, multifaceted and increasingly integrated project to ‘lock-in’ the gains of capital over labour on a global scale. The article begins with a brief introduction to the complementary projects of ‘re-designing’ and ‘locking-in’ before considering these against the historical evolution of the Lomé and Cotonou relationship
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