Divisible E-Cash from Constrained Pseudo-Random Functions

International audienceElectronic cash (e-cash) is the digital analogue of regular cash which aims at preservingusers’ privacy. Following Chaum’s seminal work, several new features were proposed for e-cash toaddress the practical issues of the original primitive. Among them,divisibilityhas proved very usefulto enable efficient storage and spendings. Unfortunately, it is also very difficult to achieve and, todate, quite a few constructions exist, all of them relying on complex mechanisms that can only beinstantiated in one specific setting. In addition security models are incomplete and proofs sometimeshand-wavy.In this work, we first provide a complete security model for divisible e-cash, and we study the linkswith constrained pseudo-random functions (PRFs), a primitive recently formalized by Boneh andWaters. We exhibit two frameworks of divisible e-cash systems from constrained PRFs achievingsome specific properties: either key homomorphism or delegability. We then formally prove theseframeworks, and address two main issues in previous constructions: two essential security notionswere either not considered at all or not fully proven. Indeed, we introduce the notion ofclearing,which should guarantee that only the recipient of a transaction should be able to do the deposit,and we show theexculpability, that should prevent an honest user to be falsely accused, was wrongin most proofs of the previous constructions. Some can easily be repaired, but this is not the casefor most complex settings such as constructions in the standard model. Consequently, we providethe first construction secure in the standard model, as a direct instantiation of our framework

A Digital Cash Paradigm with Valued and No-Valued e-Coins

Digital cash is a form of money that is stored digitally. Its main advantage when compared to traditional credit or debit cards is the possibility of carrying out anonymous transactions. Diverse digital cash paradigms have been proposed during the last decades, providing different approaches to avoid the double-spending fraud, or features like divisibility or transferability. This paper presents a new digital cash paradigm that includes the so-called no-valued e-coins, which are e-coins that can be generated free of charge by customers. A vendor receiving a payment cannot distinguish whether the received e-coin is valued or not, but the customer will receive the requested digital item only in the former case. A straightforward application of bogus transactions involving no-valued e-coins is the masking of consumption patterns. This new paradigm has also proven its validity in the scope of privacy-preserving pay-by-phone parking systems, and we believe it can become a very versatile building block in the design of privacy-preserving protocols in other areas of research. This paper provides a formal description of the new paradigm, including the features required for each of its components together with a formal analysis of its security.This research was funded by the Spanish Ministry of Science, Innovation and Universities grant number MTM2017-83271-R

A Search Theory of Money and Commerce with Neoclassical Production

This paper advances a highly tractable model with search theoretic foundations for money and neoclassical growth. In the model, manufacturing and commerce are distinct and separate activities. In manufacturing, goods are efficiently produced combining capital and labor. In commerce, goods are exchanged in bilateral meetings. The model is applied to study the effects of in ation on capital accumulation and welfare. With realistic parameters, in ation has large negative effects on welfare even though it raises capital and output. In contrast, with cash-in-advance, a device informally motivated with bilateral trading, in ation depresses capital and output and has a negligible effecton welfare. (Keywords: search, money, commerce, in ation, neoclassical production, capital accumulation, optimum quantity of money.)search, money, commerce, in;ation, neoclassical production, capital accumulation, optimum quantity of money.

Labor-Market Heterogeneity, Aggregation, and the Policy-(In)variance of DSGE Model Parameters

Data from a heterogeneous-agents economy with incomplete asset markets and indivisible labor supply are simulated under various fiscal policy regimes and an approximating representative-agent model is estimated. Preference and technology parameter estimates of the representative-agent model are not invariant to policy changes and the bias in the representative-agent model’s policy predictions is large compared to predictive intervals that reflect parameter uncertainty. Since it is not always feasible to account for heterogeneity explicitly, it is important to recognize the possibility that the parameters of a highly aggregated model may not be invariant with respect to policy changes.Aggregation, DSGE Models, Fiscal Policy, Heterogeneous-Agents Economy, Policy Predictions, Representative-Agent Models

Cryptography and Its Applications in Information Security

Nowadays, mankind is living in a cyber world. Modern technologies involve fast communication links between potentially billions of devices through complex networks (satellite, mobile phone, Internet, Internet of Things (IoT), etc.). The main concern posed by these entangled complex networks is their protection against passive and active attacks that could compromise public security (sabotage, espionage, cyber-terrorism) and privacy. This Special Issue “Cryptography and Its Applications in Information Security” addresses the range of problems related to the security of information in networks and multimedia communications and to bring together researchers, practitioners, and industrials interested by such questions. It consists of eight peer-reviewed papers, however easily understandable, that cover a range of subjects and applications related security of information

Constrained Pseudorandom Functions from Pseudorandom Synthesizers

In this paper we resolve the question of whether or not constrained pseudorandom functions (CPRFs) can be built directly from pseudorandom synthesizers. In particular, we demonstrate that the generic PRF construction from pseudorandom synthesizers due to Naor and Reingold can be used to construct CPRFs with bit-fixed predicates using the direct-line\u27\u27 approach. We further introduce a property of CPRFs that may be of independent interest

Modeling VIX And VIX Derivatives With Mean Reverting Models And Parameter Estimation Using Filter Methods

In this thesis, we study the mean reverting property of the VIX time series, and use the VIX process as the underlying. We employ various mean reverting processes, including the Ornstein-Uhlenbeck (OU) process, the Cox-Ingersoll-Ross (CIR) process and the OU processes driven by Levy processes (Levy OU) to fit historical data of VIX, and calibrate the VIX option prices. The first contribution of this thesis is to use the Levy OU process to model the VIX process, in order to explain the observed high kurtosis. To price the option using the Levy OU process, we develop a FFT method. The second contribution is to build a joint framework to consistently model the VIX and VIX derivatives together on the entire time series of market data. We choose multi-factor mean-reverting models, in which we model the VIX process as a linear combination of latent factors. To estimate the models, we use Euler approximation to find a discrete approximation for the VIX process. Based on this approximate, we consider various filter methods, namely, the Unscented Kalman Filter (UKF), constrained UKF, mixed Gaussian UKF and Particle Filter (PF) for estimation. The performances of these models are compared and discussed. Radon Nikodym derivatives of the risk-neutral measure are discussed with respect to the physical measure for the jumps. A simple dynamic trading strategy was tested on these models

Structural Econometric Methods in Auctions: A Guide to the Literature

Auction models have proved to be attractive to structural econometricians who, since the late 1980s, have made substantial progress in identifying and estimating these rich game-theoretic models of bidder behavior. We provide a guide to the literature in which we contrast the various informational structures (paradigms) commonly assumed by researchers and uncover the evolution of the eld. We highlight major contributions within each paradigm and benchmark modi cations and extensions to these core models. Lastly, we discuss special topics that have received substantial attention among auction researchers in recent years, including auctions formultiple objects, auctions with risk averse bidders, testing between common and private value paradigms, unobserved auction-speci c heterogeneity, and accounting for an unobserved number of bidders as well as endogenous entry

Proceedings of the second "international Traveling Workshop on Interactions between Sparse models and Technology" (iTWIST'14)

The implicit objective of the biennial "international - Traveling Workshop on Interactions between Sparse models and Technology" (iTWIST) is to foster collaboration between international scientific teams by disseminating ideas through both specific oral/poster presentations and free discussions. For its second edition, the iTWIST workshop took place in the medieval and picturesque town of Namur in Belgium, from Wednesday August 27th till Friday August 29th, 2014. The workshop was conveniently located in "The Arsenal" building within walking distance of both hotels and town center. iTWIST'14 has gathered about 70 international participants and has featured 9 invited talks, 10 oral presentations, and 14 posters on the following themes, all related to the theory, application and generalization of the "sparsity paradigm": Sparsity-driven data sensing and processing; Union of low dimensional subspaces; Beyond linear and convex inverse problem; Matrix/manifold/graph sensing/processing; Blind inverse problems and dictionary learning; Sparsity and computational neuroscience; Information theory, geometry and randomness; Complexity/accuracy tradeoffs in numerical methods; Sparsity? What's next?; Sparse machine learning and inference.Comment: 69 pages, 24 extended abstracts, iTWIST'14 website: http://sites.google.com/site/itwist1