Nowadays it is widely accepted to formulate the security of a protocol carrying out a given task via the “trusted-party paradigm,” where the protocol execution is compared with an ideal process where the outputs are computed by a trusted party that sees all the inputs. A protocol is said to securely carry out a given task if running the protocol with a realistic adversary amounts to “emulating” the ideal process with the appropriate trusted party. In the Universal Composability (UC) framework the program run by the trusted party is called an ideal functionality. While this simulation-based security formulation provides strong security guarantees, its usefulness is contingent on the properties and correct specification of the ideal functionality, which, as demonstrated in recent years by the coexistence of complex, multiple functionalities for the same task as well as by their “unstable” nature, does not seem to be an easy task. In this paper we address this problem, by introducing a general methodology for the sound specification of ideal functionalities. First, we introduce the class of canonical ideal functionalities for a cryptographic task, which unifies the syntactic specification of a large class of cryptographic tasks under the same basic template functionality. Furthermore, this representation enables the isolation of the individual properties of a cryptographic task as separate members of the corresponding class. By endowing the class of canonical functionalities with an algebraic structure we are able to combine basic functionalities to a single final canonical functionality for a given task. Effectively, this puts forth a bottom-up approach for the specification of ideal functionalities: first one defines a set of basic constituent functionalities for the task at hand, and then combines them into a single ideal functionality taking advantage of the algebraic structure. In our framework, the constituent functionalities of a task can be derived either directly or, following a translation strategy we introduce, from existing game-based definitions; such definitions have in many cases captured desired individual properties of cryptographic tasks, albeit in less adversarial settings. Our translation methodology entails a sequence of steps that systematically derive a corresponding canonical functionality given a game-based definition, effectively “lifting” the game-based definition to its composition-safe version. We showcase our methodology by applying it to a variety of basic cryptographic tasks, including commitments, digital signatures, zero-knowledge proofs, and oblivious transfer. While in some cases our derived canonical functionalities are equivalent to existing formulations, thus attesting to the validity of our approach, in others they differ, enabling us to “debug” previous definitions and pinpoint their shortcomings.
Decentralization has become fashionable in governmental development of the third world. Theoretically, it is the shift of sovereign responsibilities that includes the planning, financing and management of certain public functions to field units of government agencies, subordinate units or levels of government, semi-autonomous public authorities or corporations, or area-wide regional or functional authorities. Unfortunately, Bangladesh became dysfunctional due to rampant political corruption and successive political crises since its independence. Every regime has formed a local government commission under different names, without giving much real effort to decentralising their powers to the local level. Accordingly, every regime has accused their predecessors of uncontrolled distortion. The post-liberation experience of the local government (LG) of Bangladesh suggests that the national government uses the local government bodies to strengthen its own power base in the name of decentralization. The present research asks whether the policy and the formation of different structures can achieve decentralisation. It engages in a number of theoretical, methodological and empirical debates on rural local government institutions. The history of LG in Bangladesh can be characterised as a British-invented and Pakistani-installed centrally controlled local hierarchical system. Thus, because of extreme political corruption and violence in every sphere of Bangladesh, the radical potential of civil society organisations is being appropriated and they are being used to fill gaps in service delivery, allowing the state to withdraw, which is justified by 'roll-back' neoliberalism. However, this thesis argues that the restoration of law and order and assurance of transparency are prerequisites of efficient local government. Again, endorsing the traditional informal institutions can reduce the pressure on government indifferent affairs like dispute resolution, social awareness, health and safety and so on. In addition, delegating responsibility for service provision to other quarters like NGOs and civil society can help to address the development concerns of the people, as well as capacity-building in local level institutions.
A new scheme of identity authentication that has zero-knowledge characteristics is established based on RSA algorithm.The analysis of the scheme shows that the algorithm is legible,the mutual time and the opportuni-ty be cheated is less.Only one time proof,it can meet the reliability demands for which other zero-knowledge proof algorithms need much more time proof.
To provide a high level of security guarantee cryptography is introduced into the design of the voting machine. The voting machine based on cryptography is vulnerable to attacks through covert channels. An adversary may inject malicious codes into the voting machine and make it leak vote information unnoticeably by exploiting the randomness used in encryptions and zero-knowledge proofs. In this paper a voting machine resistant to covert channels is designed. It has the following properties: Firstly, it is tamper-evident. The randomness used by the voting machine is generated by the election authority. The inconsistent use of the randomness can be detected by the voter from examining a destroyable verification code. Even if malicious codes are run in the voting machine attacks through subliminal channels are thwarted. Next, it is voter-verifiable. The voter has the ability to verify if the ballot cast by the machine is consistent with her intent without doing complicated cryptographic computation. Finally, the voting system is receipt-free. Vote-buying and coercion are prevented.
2 source records
Internet Traffic Analysis and Secure E-voting
Cryptography and Data Security
Advanced Steganography and Watermarking Techniques
Many business models for smart products, like pay-per-use, require that the smart product can digitally verify whether the user has a contract with the smart product and should be granted access to privileged functionality. Traditional means to do so, e.g. password login, are very obtrusive and can thus not be applied for smart product scenarios. In this paper, we present the mechanism of association. Associations represent the abstract concept of a digitally checkable contract on the middleware level. Associations use a service for digitally representing the user that performs the tedious parts of creating a digitally checkable contract automatically. Thus, the interaction can be established unobtrusively. As this service acts on behalf of the user, the user must trust this service. We address this issue in two ways: the service is executed on the personal trusted device of the user and the user can control and inspect the actions of the service via a user interface.
The recent development in the mobile technology (mobile phones, middleware, wireless networks, etc.) created a need for new methods of protecting the code transmitted through the network. The oldest and the simplest mechanisms concentrate more on integrity of the code itself and on the detection of unauthorized manipulation. The newer solutions not only secure the compiled program, but also the data, that can be gathered during its “journey,” and even the execution state. Some other approaches are based on prevention rather than detection. In this chapter we present a new idea of securing mobile agents. The proposed method protects all components of an agent: the code, the data, and the execution state. The proposal is based on a zero-knowledge proof system and a secure secret sharing scheme, two powerful cryptographic primitives. Next, the chapter includes security analysis of the new method and its comparison to other currently more widespread solutions. Finally, we propose a new direction of securing mobile agents by straightening the methods of protecting integrity of the mobile code with risk analysis and a reputation system that helps avoiding a high-risk behavior.Request access from your librarian to read this chapter's full text.
Paul Berg-Dick, Michel Carreau, Deanne Field, Mireille Ethier
This book analyzes political decentralization and fiscal federalism in Canada and Germany, both traditional federal countries, and in Spain, a unitarian country engaged in the last two decades in a process of decentralization. Three key issues required for a well designed financing system are analyzed in depth, namely: tax assignment, equalization grants – i.e. redistribution of money from the wealthy regions or the national government to poorer regions, and the role of local governments in the administration of taxes.
We present an efficient simultaneous broadcast protocol ν-SimCast that allows n players to announce independently chosen values, even if up to t < n players are corrupt. Independence is guaranteed in the partially syn-2 chronous communication model, where communication is structured into rounds, while each round is asynchronous. The ν-SimCast protocol is more efficient than previous constructions. For repeated executions, we reduce the communication and computation complexity by a factor O(n). Combined with a deterministic extractor, ν-SimCast provides a particularly efficient solution for distributed coin-flipping. The protocol does not require any zero-knowledge proofs and is shown to be secure in the standard model under the Decisional Diffie Hellman assumption.
River floods can be very damaging. Since numerous human responses to floods are possible, the question arises: What is the organization of flood management that leads to the most efficient results? The dissertation first considers flooding and flood management in Germany. Based on that analysis, a theoretical, political-economy model of public flood defense is developed. The basic model is then extended to allow migration between upstream and downstream regions as well as between flood-prone areas and zones without risk. As different flood protection measures have quite different spatial characteristics, the distribution of responsibilities between the different actors is decisive for the overall performance of flood management. The distribution of public responsibilities among the different federal actors is crucial for two reasons. First, there are unidirectional upstream-downstream spillovers that raise the question whether decentralized or centralized provision of public goods is more efficient. Second, benefits from flood protection are concentrated to flood-prone areas near rivers. This concentration creates a natural heterogeneity of preferences for flood defense. These two aspects are also relevant for other issues in water management. Unidirectional spillovers and spatially heterogeneous preferences for public goods challenge the federal organization of flood defense. Following the lead of recent political-economy contributions to fiscal federalism, both aspects are investigated in a two region model with majority voting. Four different decision-making structures are compared: classical decentralization or centralization (based on jurisdictions containing voters both with and without preferences for the public good) and decentralized or centralized single issue authorities (whose jurisdictions, by definition, contain only high preference voters). Decentralized jurisdictions separate upstream and downstream voters, whereas a centralized jurisdiction comprises both groups. It turns out that centralized jurisdictions lead to a very low public good surplus and that either classical decentralization or decentralized single issue authorities achieve the best results under most conditions. The centralized provision of public goods is flawed because there is either an extreme over- or an extreme under-provision of the downstream public good. This can, however, be mitigated if there is a common standard for flood protection or if only the upstream provision of the public good is centralized. Whether or not these two solutions are beneficial depends on the magnitude of spillovers and also on the voting majorities in the two regions. Expanding the model to consider migration led to more complex results. First, citizens can migrate to flood-prone areas. Such migration flows can be induced by too large public flood defense, which is favored if citizens outside of flood-prone areas also finance the public good. Second, migration flow is also influenced by spillovers. The socially efficient population distribution is U-shaped with respect to spillovers. With symmetry assumptions, negative as well as positive unidirectional spillovers favour larger downstream populations. With myopic voters that neglect migration flow, this pattern is not achieved and the downstream population is large for positive spillovers and small for negative spillovers. Centralized jurisdictions are preferable to decentralized ones for smaller spillover effects if migration is possible. This argument is even stronger if voters take migration responses to the provision of public goods into account. The results shed light not only on the federal organization of flood management, but also on the institutional difficulties that arise from the current policy paradigm of the river basin approach to water management.
Modeling security for protocols running in the complex network environment of the Internet can be a daunting task. Ideally, a security model for the Internet should provide the following guarantee: a protocol that implements a particular task specification will retain all the same security properties as the specification itself, even when an arbitrary set of protocols runs concurrently on the same network. This guarantee must hold even when other protocols are maliciously designed to interact badly with the analyzed protocol, and even when the analyzed protocol is composed with other protocols. The popular Universal Composability (UC) security framework aims to provide this guarantee.
Unfortunately, such strong security guarantees come with a price: they are impossible to achieve without the use of some trusted setup. Typically, this trusted setup is global in nature, and takes the form of a Public Key Infrastructure (PKI) and/or a Common Reference String (CRS). However, the current approach to modeling security in the presence of such setups falls short of providing expected security guarantees. A quintessential example of this phenomenon is the deniability concern: there exist natural protocols that meet the strongest known security notions (including UC) while failing to provide the same deniability guarantees that their task specifications imply they should provide.
We introduce the Generalized Universal Composability (GUC) framework to extend the UC security notion and enable the re-establishment of its original intuitive security guarantees even for protocols that use global trusted setups. In particular, GUC enables us to guarantee that secure protocols will provide the same level of deniability as the task specification they implement. To demonstrate the usefulness of the GUC framework, we first apply it to the analysis and construction of deniable authentication protocols. Building upon such deniable authentication protocols, we then prove a general feasibility result showing how to construct protocols satisfying our security notion for a large class of two-party and multi-party tasks (assuming the availability of some reasonable trusted setup). Finally, we highlight the practical applicability of GUC by constructing efficient protocols that securely instantiate two common cryptographic tasks: commitments and zero-knowledge proofs.
A fair exchange protocol allows two parties to exchange items in a fair way so that either each party gets the other's item or neither party does. In this paper, we propose a key-exposure-free chameleon hashing scheme based on the discrete logarithm assumption, and prove that it enjoys all advantages of previous schemes: collision resistant, semantic security, message hiding and key exposure freeness. Using this new scheme as kernel, an efficient and secure chameleon-based optimistic fair exchange protocol is proposed. Unlike the vast majority of previously proposed protocols, above approach has no use for verifiably encrypted signature and does not use any zero knowledge proofs, which avoids most of the costly computations. The security of the newly devised protocol is also examined. It is showed that the proposed scheme is secure and efficient.
This book analyzes political decentralization and fiscal federalism in Canada and Germany, both traditional federal countries, and in Spain, a unitarian country engaged in the last two decades in a process of decentralization. Three key issues required for a well designed financing system are analyzed in depth, namely: tax assignment, equalization grants – i.e. redistribution of money from the wealthy regions or the national government to poorer regions, and the role of local governments in the administration of taxes.
Public institutions have recently been faced with multiple challenges arising from increased \ncompetition from the private sector and public scrutiny. To remain competitive as well as \nprofitable, some have resulted to privatization. The Kenya Tea Development Authority has faced \nserious challenges both in the internal operating and external environment which required urgent \nattention to avoid any serious impact in the local tea industry. This was made worse by global \ndevelopments in the tea industry, resulting in low returns in the entire tea value chain and the \nfarm level. KTDA therefore needed to position itself to increase its competitiveness, global \nmarket share and increase returns. The objectives of the study were to establish the approaches \nthat KTDA Ltd had used in its privatization process and also, the challenges it encountered in its \nprivatization. \nThis was a case study which sampled ten employees thus achieving a 100% response rate. Both \nprimary and secondary data were collected. Primary data was collected through face to face \ninterviews and also through self administered semi-structured questionnaires. Data was analyzed \nusing frequencies, means and standard deviations. These were presented in tabular format. \nQualitative data was analyzed using content and factor analysis. \nThe research findings revealed that various approaches implemented by KTDA towards \nachieving its privatization were not well defined to most stakeholders. It was evident that the \nneed to plan ahead, pressure from stakeholders and response to customer needs were viewed as \nthe important factors that necessitated the privatization. The objectives of the privatization \naccording to those interviewed were to increase competitiveness of KTDA Ltd and reduce costs. \nIt was evident that privatization changes were largely initiated at the top management level and \nthe privatization vision was clearly articulated, nor understood by all staff. The privatization \nprocess faced rather strong resistance from stakeholders, due to issues such as, parochial self \ninterest, fear of the unknown, fear of inability to develop relevant skills among other factors. In \nan attempt to react to these factors, training and education, communication, use of local change \nleaders, promise of reward, coercion and authority, manipulation and use of reward were the \ncommonly used mechanisms. Other factors that had hindered the privatization process were \ninterference by factories and politicians. Out of the set out objectives, interviewees agreed that \nthe privatization had enabled KTDA Ltd to operate on autonomous basis, as well as enhancing \nefficiency of the organization, while the main key successes factors present included properly \ntrained staff to manage the privatized institution and who are well equipped to drive the business. \nIt was however recommended that for an effective privatization of KTDA Ltd to take place, the \nshareholding structure of the organization and the factory companies should be restructured. The \ndual role of KTDA Ltd as a management agent and a tea grower's investment issue should be \naddressed to avoid the current confusion with a subsidiary company being formed to manage the \nfactories. The organization should further decentralize its function to the regional offices to \nenhance service delivery to the various factories. Implementation of proper management of the \nhuman capital and good corporate governance policies are paramount factors for streamlining the \nprivatization process of KTDA Ltd.
Zuzana Beerliová-Trubíniová, Martin Hirt, Jesper Buus Nielsen
Abstract. Secure multiparty computation (MPC) allows a set of parties to securely evaluate any agreed function of their inputs, even when up to t of the n parties are faulty. Protocols for synchronous networks (where every sent message is assumed to arrive within a constant time) tolerate up to t < n/2 faulty parties, whereas in the more realistic asynchronous setting (with no a priory information on maximal message delay) only security against t < n/3 is possible. Note that even asynchronous Byzantine agreement requires t < n/3. In this paper, we are interested in the minimal synchronicity assumption for achieving security against t < n/2. It turns out that the bottleneck of asynchronous MPC is the distribution of the inputs: Once the inputs are correctly distributed, any deterministic function can be computed over a fully asynchronous network with t < n/2. Furthermore, we show that the inputs can be verifiably distributed with t < n/2, if a single round of synchronous broadcast is available. Composing the above, we obtain the first MPC protocol that achieves security against t < n/2 without assuming a fully synchronous network. Actually our protocol guarantees security against any faulty minority in an almost asynchronous network, i.e. in a network with one single round of synchronous broadcast (followed by a fully asynchronous communication). Furthermore our protocol takes inputs of all parties (in a fully asynchronous network only inputs of n−t parties can be guaranteed), and so achieves everything that is possible in synchronous networks (but impossible in fully asynchronous networks) at the price of just one synchronous broadcast round. As tools for our protocol we introduce the notions of almost non-interactive verifiable secret-sharing and almost non-interactive zero-knowledge proof of knowledge, which are of independent interest as they can serve as efficient replacements for fully non-interactive verifiable secret-sharing and fully non-interactive zero-knowledge proof of knowledge.
The selective decommitment problem can be described as follows: assume an adversary receives a number of commitments and then may request openings of, say, half of them. Do the unopened commitments remain secure? Although this question arose more than twenty years ago, no satisfactory answer could be presented so far. We answer the question in several ways: 1. If simulation-based security is desired (i.e., if we demand that the adversary's output can be simulated by a machine that does not see the unopened commitments), then security is not achievable for non-interactive or perfectly binding commitment schemes via black-box reductions to standard cryptographic assumptions. However, we show how to achieve security in this sense with interaction and a non-black-box reduction to one-way permutations. 2. If only indistinguishability of the unopened commitments from random commitments is desired, then security is not achievable for (interactive or non-interactive) perfectly binding commitment schemes, via black-box reductions to standard cryptographic assumptions. However, any statistically hiding scheme does achieve security in this sense. Our results give an almost complete picture when and how security under selective openings can be achieved. Applications of our results include: • Essentially, an encryption scheme must be non-committing in order to achieve provable security against an adaptive adversary. • When implemented with our secure commitment scheme, the interactive proof for graph 3-coloring due to Goldreich et al. becomes zero-knowledge under parallel composition. On the technical side, we develop a technique to show very general impossibility results for black-box proofs.
This paper covers network investment problems under decentralized control of regulation, infrastructure ownership and management. The model features two countries managing domestic infrastructures, used simultaneously for downstream international service provision. Initially, the welfare losses from non-cooperative investment financing policy and access pricing are derived. The impact of strategic interaction between the countries' access prices on the choice of financing policy is investigated. Under strict budget balancing, there are no incentives for efficiency improving investments. Further, investment coordination is shown useless in the absence of regulatory coordination. Illustrations from European network regulation policy for energy and rail are presented.
This book analyzes political decentralization and fiscal federalism in Canada and Germany, both traditional federal countries, and in Spain, a unitarian country engaged in the last two decades in a process of decentralization. Three key issues required for a well designed financing system are analyzed in depth, namely: tax assignment, equalization grants – i.e. redistribution of money from the wealthy regions or the national government to poorer regions, and the role of local governments in the administration of taxes.
This book analyzes political decentralization and fiscal federalism in Canada and Germany, both traditional federal countries, and in Spain, a unitarian country engaged in the last two decades in a process of decentralization. Three key issues required for a well designed financing system are analyzed in depth, namely: tax assignment, equalization grants – i.e. redistribution of money from the wealthy regions or the national government to poorer regions, and the role of local governments in the administration of taxes.