Blockchain Papers

Markus Jakobsson, Moti Yung

No abstract is available for this record.

Hoi‐Kwong Lo, H. F. Chau

There had been well known claims of unconditionally secure quantum protocols for bit commitment. However, we, and independently Mayers, showed that all proposed quantum bit commitment schemes are, in principle, insecure because the sender, Alice, can almost always cheat successfully by using an Einstein-Podolsky-Rosen (EPR) type of attack and delaying her measurements. One might wonder if secure quantum bit commitment protocols exist at all. We answer this question by showing that the same type of attack by Alice will, in principle, break any bit commitment scheme. The cheating strategy generally requires a quantum computer. We emphasize the generality of this ``no-go theorem'': Unconditionally secure bit commitment schemes based on quantum mechanics---fully quantum, classical or quantum but with measurements---are all ruled out by this result. Since bit commitment is a useful primitive for building up more sophisticated protocols such as zero-knowledge proofs, our results cast very serious doubt on the security of quantum cryptography in the so-called ``post-cold-war'' applications. We also show that ideal quantum coin tossing is impossible because of the EPR attack. This no-go theorem for ideal quantum coin tossing may help to shed some lights on the possibility of non-ideal protocols.

Jacques Stern

The present paper investigates the possibility of designing zero-knowledge identification schemes based on hard problems from coding theory. Zero-knowledge proofs were introduced by Goldwasser, Micali, and Rackoff (1985). Their practical significance was soon demonstrated in the work of Fiat and Shamir [1986], who turned zero-knowledge proofs of quadratic residuosity into efficient means of establishing user identities. In the present paper, we propose a new identification scheme, based on error-correcting codes, which is zero-knowledge and seems of practical value. Furthermore, we describe several variants, including one which has an identity-based character. The security of our schemes depends on the hardness of finding a word of given syndrome and prescribed (small) weight with respect to some randomly generated binary linear error-correcting code. This is, of course, not the first attempt to design a cryptographic scheme using tools from coding theory. The difference is that identification protocols do not follow the public key paradigm based on trap-door functions and described in the seminal Diffie-Hellman paper [1976]. Rather, they only require one-way functions, which opens the way to using, in a rather direct manner, simple combinatorial problems of the kind provided by coding theory. The resulting schemes compare favorably to their number-theoretic analogs.

Shai Halevi, Silvio Micali

No abstract is available for this record.

Vincent Peloso, Barbara A. Tenenbaum

Looking at the Latin American liberal project during the century of postindependence, this collection of original essays draws attention to an underappreciated dilemma confronting liberals: idealistic visions and fiscal restraints. Liberals, Politics, and Power focuses on the inventiveness of nineteenth-century Latin Americans who applied liberal ideology to the founding and maintenance of new states. The impact of liberalism in Latin America, the contributors show, is best understood against the larger backdrop of struggles that pitted regional demands against the pressures of foreign finance, a powerful church against a decentralized state, and aristocratic desire to retain privilege against rising demands for social mobility.Moving beyond the traditional historiographical division between Eurocentric and dependency theories, the essays attempt to account for a uniquely Latin American liberal ideology and politics by exploring the political dynamics of such countries as Mexico, Colombia, Argentina, and Peru. Contributors discuss liberal efforts to build a viable legal order through elections and to implement a means of public finance that could fund the states' operations. Essays that span the entire century address issues such as the emergence of caudillos, the role of artisans, and popular participation in elections in light of fiscal, and other, impediments to progress.In their introduction, Vincent C. Peloso and Barbara A. Tenenbaum provide a hemispheric overview of liberalism that illustrates its similarities across Latin America. By exploring the liberal constitutional and economic order lying beneath apparently dictatorial states, this pathbreaking volume underlines the importance of fiscal policy in the fashioning of state power. Liberals, Politics, and Power serves not only as a guide to the liberal principles and practices that governed state formation in nineteenth-century Latin America but also as a means to evaluate the complex relationship between ideas and practical politics.

Alfredo De Santis, Giovanni Di Crescenzo, Oded Goldreich, Giuseppe Persiano

The input to the Graph Clustering Problem consists of a sequence of integers m 1 ; :::; m t and a sequence of P t i=1 m i graphs. The question is whether the equivalence classes, under the graph isomorphism relation, of the input graphs have sizes which match the input sequence of integers. In this note we show that this problem has a (perfect) zero-knowledge interactive proof system. Keywords: Graph Isomorphism, Zero-Knowledge Interactive Proofs. 1 Introduction The remarkable notion of perfect zero-knowledge proofs was introduced by Goldwasser, Micali and Rackoff [GoMiRa]. A perfect zero-knowledge proof system is a method for a prover to convince a polynomial-time bounded verifier with very high probability that a certain assertion is true without revealing any additional information (in an information-theoretic sense). Not many are the languages which have been shown to have a perfect zero-knowledge proof system; in particular, all of them share number-theoretic or random self-red...

Richard H. Acker, Daniel M. Kammen

No abstract is available for this record.

Robin Boadway, Isao Horiba, Raghbendra Jha, Boadway, Robin · 6 authors

It has realized since Pigou (1947) that if public goods are financed by distortionary taxation, the marginal social cost of providing the public good will exceed the actual resource cost by the marginal deadweight cost of taxation.

Ronald Cramer, Ivan Damgård

We present a 4-move zero-knowledge proof system [21] for any NP language L, which allows showing that x 2 L with error probability less than 2 \\Gammak using communication corresponding to O(jxj c )+O(k) bit commitments, where c is a constant depending only on L. We also present a 4-move perfect zero knowledge interactive argument for any NP-language L. On input x 2 L, the communication complexity is O(jxj c ) \\Delta max(k; l) bits, where l is the security parameter for the prover 1 . The protocols can be based on any bit commitment scheme with a particular set of properties. We suggest efficient implementations based on discrete logarithms or factoring. As a function of the security parameters, our protocols have the smallest known asymptotic communication complexity among general proofs or arguments for NP. Moreover, the constants involved are small enough for the protocols to be practical in a realistic situation: our protocols allows proving/arguing satisfiability of a Boo...

Mark Bray

No abstract is available for this record.

Bonnie J. Knutson, Martin Malk, Raymond S. Schmidgall

Most directors of marketing intuitively know that accepting some business has an opportunity cost of not being able to accept potentially more lucrative business. The decision becomes particularly critical when the prospective contract is for a large event, such as a conference. Some hotels address this matter by, for instance, requiring executive committee approval for all large contracts or all business that involves function space. The decision can be made much earlier and more simply by individual sales representatives or sales managers, however, if they analyze the tradeoffs of any potential contract. An analytical approach can be built into a spreadsheet calculation that takes into account such variables as special room rates, potential banquet revenues and costs, and revenues and costs of other services (e.g., audio-visual support). The decision is more than quantitative, however, and must take into account such factors as the effect on other guests' perceptions of the hotel if, say, facilities are jammed by conventioneers. Those effects cannot be modeled on a spreadsheet and are subject to the marketing director's judgment.

Carolyn Johnson, Theresa A. Nicklas, Gerald S. Berenson

No abstract is available for this record.

Stanley A. Kochanek

T HE PROLIFERATION OF INTEREST GROUPS and the explosion of group advocacy in the United States and other liberal democracies in the 1980s has led to a renewed attention to the comparative study of interest politics. Among the major questions at issue is the relationship between political, social and economic change and group formation, proliferation, organizational maintenance and group action. Interest group theory suggests that groups proliferate during periods of rapid change. As India approaches its first half century of independence, a study of changes in its interest group system provides an excellent opportunity to attempt to assess the impact of systemic change on interest group development and behavior.' In the decades since independence and especially since 1980, India has experienced an accelerated process of economic, social and political change. The Indian rate of economic growth has increased, literacy rates have risen sharply, the pace of urbanization has quickened and most importantly the size of its middle class has increased significantly. These economic and social changes have been accompanied by striking political and policy changes that include the decline of party, heightened pressure for decentralization and fundamental alteration of India's past model of planned development. These changes have begun to alter the nature and conduct of interest politics in India. India has experienced an increase in the mobilization, proliferation and transformation of groups and significant changes in interest group roles, styles and strategies. As a result the Indian system of state-dominated pluralism in which autonomous groups were overshadowed by an omnipresent state2 is eroding as interest politics have

Yung‐Hsiang Chen, Tzonelih Hwang

No abstract is available for this record.

Priscilla Wohlstetter, Richard J. Wenning, Kerri L. Briggs

By the end of 1994, 11 states had passed legislation authorizing charter schools. Following the argument that charter schools need to be autonomous, self-governing organizations to enhance their potential for high performance, this study explores legislative conditions that promote charter school autonomy. The study applies a conceptual framework of autonomy to assess variations among state charter school policies. 7he results suggest that state policies offer different levels of autonomy and thus charter schools will vary in their ability to innovate and in their potential for high performance. Differences in autonomy across charter school laws appear to be related to state political cultures and to the state's history of decentralization reform.

Michael L. Nance, Francis C. Nance

No abstract is available for this record.

Joan Boyar, Gilles Brassard, René Peralta

The communication complexity of zero-knowledge proof systems is improved. Let C be a Boolean circuit of size n. Previous zero-knowledge proof systems for the satisfiability of C require the use of Omega (kn) bit commitments in order to achieve a probability of undetected cheating not greater than 2/sup -k/. In the case k=n, the communication complexity of these protocols is therefore Omega (n/sup 2/) bit commitments. A zero-knowledge proof is given for achieving the same goal with only O(n/sup m/+k square root n/sup m/) bit commitments, where m=1+ epsilon /sub n/ and epsilon /sub n/ goes to zero as n goes to infinity. In the case k=n, this is O(n square root n/sup m/). Moreover, only O(k) commitments need ever be opened, which is interesting if committing to a bit is significantly less expensive than opening a commitment.>

Richard Shillito, Eric Barendt

Abstract Dissatisfaction with the law of libel has been prevalent for some time. Critics have pointed to three areas in particular as requiring reform. First, they have said that rules of pleading in libel actions are unnecessarily arcane and that the interlocutory process is unduly complex. Secondly, it is said that awards of damages are out of proportion to the loss suffered. One consequence is that defendants have in general thrown more legal resources into litigation, which in turn has increased the costs penalty for the unsuccessful litigant. A third criticism is that the balance between plaintiff and defendant, both procedurally and in relation to the burden of proof, may be tilted too far in the plaintiff’s favour. (The suggestion that, perhaps, the burden of proof ought to be reversed and placed on the plaintiff has gained increased respectability, though it has not convinced everyone.) An important incidental effect of these deficiencies in the law, say critics, is that recourse to law is too complex and expensive. The result is that, at one extreme, the impecunious plaintiff may be deprived of a remedy and, on the other hand, with so much at stake financially for the unsuccessful defendant, the law may fetter freedom of speech.

Suresh M. Joshi, Ebrahim Maghami, Atul Kelkar

Control system design is considered for attitude control and vibration suppression of flexible space structures. The problem addressed is that of controlling both the zero-frequency rigid-body modes and the elastic modes. Model-based compensators, which employ observers tuned to the plant parameters, are first investigated. Such compensators are shown to generally exhibit high sensitivity to the knowledge of the parameters, especially the elastic mode frequencies. To overcome this problem, a class of dynamic dissipative compensators is next proposed which robustly stabilize the plant in the presence of unmodeled dynamics and parametric uncertainties. An analytical proof of robust stability is given, and a method of implementing the controller as a strictly proper compensator is described. Methods of designing such controllers to obtain optimal performance and robust stability are presented. Numerical and experimental results of application of the methods are presented, which indicate that dynamic dissipative controllers can simultaneously provide excellent performance and robustness.>

Yoshiteru Ishida

The self-organizing diagnosis has been studied by applying the idea of autonomous and decentralized systems extracted from the concept of immune network. The model implements network-level recognition by connecting information from local recognition units by dynamical evaluation chain. The model has been further elaborated for engineering concerns of identifying not only sensor faults but process faults. The sensor faults will be identied by evaluating reliability of data from sensor, while the process faults will be identied by evaluating that of constraints that must be satised among these data. We have demonstrated that the extended sensor network will work against both sensor faults and process faults by an illustrative example.

Xing‐Yuan Gu, Sheng‐Lan Tang, Su‐Hua Cao

The socio-economic reforms launched in China in the late 1970s led to rapid economic growth and, with it, health sector resources expanded rapidly. The rural health services have benefited from the policies of economic reform, but not in an optimal way, particularly in poor areas. This article uses a case study of a poor county--Donglan--to illustrate that the fiscal decentralization combined with the financial responsibility system have resulted in a weakening of financing and provision of rural health services in poor areas. The need for health facilities to generate revenue has had unfortunate consequences for the style of medical care, such as over-prescription. In addition, the collapse of the cooperative medical system and the weakening of the three-tier network of rural health care in Donglan have jeopardized preventive programs and threaten access to basic health care for the peasants, especially the poor. The study found evidence that preventive programs have deteriorated over the past years, the poor had financial difficulty in access to services, particularly hospital care, health facilities at township and village levels have been run down, and less training and supervision have been provided by upper-level health facilities. The article concludes with recommendations for a strategy for rebuilding and strengthening the three-tier network of rural health care, and for establishing a cooperative medical and health care scheme to ensure that the majority of peasants in Donglan can be guaranteed access to basic health services. Limited health resources will therefore be better used.

Sharon S. Ehrmeyer, Ronald H. Laessig

All decentralized testing is regulated according to the Clinical Laboratory Improvement Amendments of 1988. Two organizations, the Joint Commission on Accreditation of Health Care Organizations and the College of American Pathologists, have received deemed status for their voluntary standards from the Health Care Financing Administration. Deemed status means that the organizations' voluntary standards meet or exceed the federal requirements. The decentralized testing sites can exercise several options in determining which organization, and hence which set of standards, will be used to regulate their testing processes. In this article, the authors outline the various regulatory requirements, provide insight into the relationship of each, and offer a framework for decentralized testing sites to follow to meet the requirements.

M. Dewatripont, Eric Maskin

We study a credit model where, because of adverse selection, unprofitable projects may nevertheless be financed. Indeed they may continue to be financed even when shown to be low-quality if sunk costs have already been incurred. We show that credit decentralization offers a way for creditors to commit not to refinance such projects, thereby discouraging entrepreneurs from undertaking them initially. Thus, decentralization provides financial discipline. Nevertheless, we argue that it puts too high a premium on short-term returns. The model seems pertinent to two issues: “soft budget constraint” problems in centralized economies, and differences between “Anglo-Saxon” and “German-Japanese” financing practices.

Laura Levitt

Embracing, Ambiguities. EMBRACING, AMBIGIDTIES. by Laura Levitt Laura Levitt works as an Assistant Professor of Religion at Temple University, teaching also in the Women's Studies Program. Her writing attends to feminist theory and contemporary Jewish culture. She is the author of the forthcoming book Ambivalent Embraces: Jewish Feminist Identities as Home (New York: Routledge). 131 Perhaps "embrace" is an odd way to explain a methodological turn in one's work, but it captures well the way I work with texts. According to·The American Heritage Dictionary, to "embrace" means: To clasp or hold with arms, usually as an expression of affection.... To surround; enclose.... To twine around. . .. To include as part of something broader. . . . To take up willingly or eagerly. . . . An act of holding close with the arms, usually as an expression ofaffection; a hug.... An enclosure or encirclement. . . . Eager acceptance.1 Implicit in this definition is a desire, an attraction that calls for a response. An embrace is such a response. But in acting on such a desire, there is already a tension. Although an embrace can be a loving gesture, a tender act of affection, or protection, it has other connotations. To hold is also to assume control over another, even, and perhaps especially, the other who is the object of one's affection. In the American Heritage to "embrace" is to surround or enclose. One may hold on too tight, not allowing the other enough space to breathe and to grow on their own. When I think about being entwined I worry about the damage done by vines like kudzu that take over all that comes into their grasp. These vines kill the trees and bushes within their embrace. lThe American Heritage Dictionary of the English Language, Third Edition, (Boston, Houghton, Mimin Company, 1992). 132 SHOFAR Fall 1995 Vol. 14, No.1 Reading is about desire, and about different kinds of embraces. In reading a text, something brings you in, captures your imagination, hooks you. To embrace a text is to give yourself to these desires. This is a joy, but with dangers. One danger is holding on too tightly; the text loses its distinct character and becomes a reflection of the reader. The reader takes the text into herself. It becomes an extension of her. Another danger, an inversion of the first: the reader loses herself in the text. Whereas in the first danger, the text gets swallowed, here the reader's difference dissolves. She is reduced to another instance ofthe text's argument. In becoming the text, she loses her own voice by taking on that of the text. Both of these forms ofreading blur boundaries. Distinctions between reader and text are lost. This blurring of distinctions gets tricky when such reading is accompanied by, and part of, one's writing. In writing we stake out positions and this feels risky. Yet, what goes on in forms of writing-such as academic scholarship-that depend on citations of other writers' texts? Sometimes finding and staking out one's own positions happens in response, while reading texts with similar commitments. Their similarities offer a kind of (em)brace. They hold us up as we attempt to take a stand, especially for the first time. Citations of other people's writing can brace our own argument. They provide weight, authority, and precedent. But sometimes in this process, one of the writers gets lost. As readers who write about other people's writing, we can lose our own voices, holding on too tightly to the authority of other people's writing. And so in writing this essay, I find myself a bit wobbly. There are texts that I want to bring into this discussion, passages I want to cite as proof for what I am saying. For the moment, I will resist the temptation. I will let my words stand alone. I have been able to find my voice as a writer by reading and engaging with the texts of others. The text that speaks to me right now-pushing through the seams of my essay with such force that I can barely keep myself from quoting it at length-is Susan Rubin Suleiman's Risking Who...