Background Over the past two decades the quest for safe blood supply has led to tremendous growth in the content and scope of the science and practice of Transfusion Medicine (TM). The desire by the various stakeholders in the blood establishment for zero‐risk blood transfusion has not only stretched the level of quality expected of the Transfusion Medicine Service to apical height, but has also resulted in the demand by these stakeholders for concrete proofs that expected degrees of quality have been met or preferably exceeded. Quality indicators (QIs) are a Quality Management System (QMS) tool that are instituted in an organization with intent on not just providing this much needed proof of the level of quality performance tenable in the organization, but they are also intent on utilizing the information gained to seek improving the quality of performance in the organization. In the last decade, huge efforts have been exerted by government and non‐government hospital‐based blood banks, national and international organizations to collate, select, establish and analyze quality QIs for several dimensions of healthcare quality. Notable contributions have been made by such eminent bodies as the Agency for Healthcare Research and Quality (AHRQ), the Organization for Economic Cooperation and Development (OECD) and the College of American Pathologists (CAP). Unfortunately these efforts have only sparsely addressed quality indicators for TM. A year ago, the International Society of Blood Transfusion (ISBT) instituted its Working Party on Quality Management (WPQM). Quality indicators for TM are of priority to the WPQM which presumably is intent on redressing this imbalance and providing robust and valid quality indicators to monitor quality performances in key processes and outcomes in TM practice, globally. Objective This paper therefore highlights some basic essentials for successful monitoring of quality of transfusion medicine service through appropriate selection and implementation of quality indicator projects. It is hoped the information shared through this medium might be of value to Transfusion Medicine practitioners as well as to the ISBT WPQM as they thinker with quality indicators for Transfusion Medicine. Material and Method Considerable review of published literature in the form of journal articles, books and online publications on quality management and quality indicators in Healthcare/Transfusion Medicine was performed with the view to extract essentials elements that could be considered building blocks for the selection, implementation, analysis and utilization of quality indicators in Transfusion Medicine. Result Elements deemed as essential building blocks that were appraised included, but were not limited to: understanding Transfusion Medicine terrain; concept of quality and quality indicators selection criteria; choice of improvement model, data analysis and manner of communication of findings as well as the role of effective education and leadership. Conclusion Quality indicators are indispensible tools which various stakeholders in the Blood Transfusion establishment now demand to adjudge and improve on quality performance. Practitioners as well as policy makers in Transfusion Medicine need to ensure that the quality indicators they institute are appropriately selected and analyzed to be effective and efficient monitors of quality. Knowledge of basic building blocks discussed here is therefore a fundamental prerequisite.
A public watermark detection scheme using verifiable secret sharing is proposed. It removes the expensive zero-knowledge interactive proofs and replaces the traditional trusted third party with a group of proxies. Moreover, the scheme is secure against sensitivity attacks and very efficient in terms of computation cost, the number of rounds and bandwidth required in the communications.
Open access
Advanced Steganography and Watermarking Techniques
L'interpretazione astratta è una teoria che formalizza l'approssimazione conservativa della semantica di sistemi informatici hardware e software, focalizzandosi su alcune proprietà, che espresse mediante opportune strutture algebriche (domini astratti) possono essere calcolate in modo corretto (anche se non completo). Una grande varietà di domini astratti può essere elaborata, a aseconda dei contesti di applicazione, e con scelta dei domini astratti è possibile modulare in modi diversi precisione e complessità computazionale. Questa tesi considera l'applicazione di tecniche di Interpretazione Astratta in tre diversi scenari: Program slicing; Watermarking di database relazionali; Watermarking del codice sorgente di programmi. Relativamente al Program slicing, viene proposto un raffinamento delle tecniche tradizionali già presenti in letteratura. Molto spesso, siamo interessati a una specifica proprietà delle variabili in un criterio di slicing, piuttosto che ai suoi effettivi valori. Questo è il caso, ad esempio, quando si analizza la non-interferenza in language-based security, dove le astrazioni entrano in gioco per modellare il potere osservativo degli attaccanti. In questo scenario, lo slicing tiene in considerazione le proprietà astratte delle variabili e le dipendenze astratte. Questo approccio allo slicing, non è solo la generalizzazione della tecnica tradizionale, ma offre nuovi spunti nelle relazioni tra diverse aree di ricerca dell'informatica. Un secondo scenario di applicazione delle tecniche di Interpretazione Astratta è la progettazione di watermarking di database relazionali, la cui rilevanza è legata al fatto che in Internet è molto importante preservare i diritti di proprietà nei database relazionali mantenuti in outsourcing. In tale ambito, viene proposta una tecnica di watermarking senza distorsione, che migliora la verifica dell'integrità dei database relazionali utilizzando un meccanismo di autenticazione pubblica. L'ultimo scenario considerato è quello del Watermarking del codice sorgente di programmi: all'aumentare della quantità di codice sorgente distribuito sul web, la protezione e il rilevamento delle proprietà del software è diventata una questione importante. Nella tesi, viene presentato uno schema di watermarking software a chiave pubblica (watermarking asimmetrico), basato su tecniche di trasformazione che preservano la semantica, e che è simile nello spirito alle zero-knowledge proofs. L'approccio proposto si pone come un'alternativa alla cifratura e l'autenticazione software piuttosto che come uno strumento per la protezione del copyright.
In this paper, we study methods for improving the utility and privacy of\nreputation scores for online auctions, such as used in eBay, so as to reduce\nthe effectiveness of feedback extortion. The main ideas behind our techniques\nare to use randomization and various schemes to escrow reputations scores until\nappropriate external events occur. Depending on the degree of utility and\nprivacy needed, these external techniques could depend on the number and type\nof reputation scores collected. Moreover, if additional privacy protection is\nneeded, then random sampling can be used with respect reputation scores in such\na way that reputation aggregates remain useful, but individual reputation\nscores are probabilistically hidden from users. Finally, we show that if\nprivacy is also desired with respect to the the reputation aggregator, then we\ncan use zero-knowledge proofs for reputation comparisons.\n
We study the Glauber dynamics for the zero-temperature Ising model in dimension d=4 with "plus" boundary condition.Let T+ be the time needed for an hypercube of size L entirely filled with "minus" spins to become entirely "plus". We prove that T+ is O(L^2(log L)^c) for some constant c, not depending on the dimension. This brings further rigorous justification for the so-called "Lifshitz law" T+ = O(L^2) [5, 3] conjectured on heuristic grounds. The key point of our proof is to use the detail knowledge that we have on the three-dimensional problem: results for fluctuation of monotone interfaces at equilibrium and mixing time for monotone interfaces dynamics extracted from [2], to get the result in higher dimension.
We study the Glauber dynamics for the zero-temperature Ising model in\ndimension d=4 with "plus" boundary condition.Let T+ be the time needed for an\nhypercube of size L entirely filled with "minus" spins to become entirely\n"plus". We prove that T+ is O(L^2(log L)^c) for some constant c, not depending\non the dimension. This brings further rigorous justification for the so-called\n"Lifshitz law" T+ = O(L^2) [5, 3] conjectured on heuristic grounds. The key\npoint of our proof is to use the detail knowledge that we have on the\nthree-dimensional problem: results for fluctuation of monotone interfaces at\nequilibrium and mixing time for monotone interfaces dynamics extracted from\n[2], to get the result in higher dimension.\n
In this paper, we study methods for improving the utility and privacy of reputation scores for online auctions, such as used in eBay, so as to reduce the effectiveness of feedback extortion. The main ideas behind our techniques are to use randomization and various schemes to escrow reputations scores until appropriate external events occur. Depending on the degree of utility and privacy needed, these external techniques could depend on the number and type of reputation scores collected. Moreover, if additional privacy protection is needed, then random sampling can be used with respect reputation scores in such a way that reputation aggregates remain useful, but individual reputation scores are probabilistically hidden from users. Finally, we show that if privacy is also desired with respect to the the reputation aggregator, then we can use zero-knowledge proofs for reputation comparisons.
As costly and spectacular art museums have proliferated since the opening of Frank Gehry's Bilbao Guggenheim, some critics have complained that “flash and bravura win out over contemplation…and architecture triumphs over art.”1 Hal Foster has even declared that museums like Gehry's Bilbao “inflate the contemporary museum into a gigantic spectacle‐space that can swallow any art, let alone any viewer, whole.”2 The problem is not that bold exteriors outshine the art, but that strange curves, odd angles, or enormous heights inside may generate a “spectacle‐space” that interferes with our attention to the art.3 For example, a number of the acutely angled gallery walls of Daniel Libeskind's 2006 Denver Art Museum addition slant inward or outward in ways that many people have found intrusive. But other critics have been willing to overlook functional defects in favor of audacious formal qualities, even if not all would go as far as Phillip Johnson's “if the architecture is as good as in Bilbao, fuck the art!”4 These conflicting responses to dramatic art museum architecture seem to reflect two deeper intuitions about architecture in general: it seems only natural to expect aesthetics and function to complement each other in architecture, yet it also seems natural to overlook functional defects when aesthetic qualities are outstanding. In this article, I will suggest a way to reconcile these two intuitions by outlining a perspective I call “moderate functionalism.” Moderate functionalism tries to avoid the faults of two polar positions on aesthetics and function in contemporary philosophy of architecture. One position, going back to Roger Scruton's Aesthetics of Architecture and recently updated by Edward Winters, accepts the necessity of function in general but denies the aesthetic relevance of particular functions, a position that would justify those who give priority to formal audacity in art museum architecture.5 At the opposite pole, Glenn Parsons and Allen Carlson's “functional beauty” proposal would make aesthetic appreciation directly depend on a building satisfying its “proper” function, a position that would support those who champion the priority of a museum's exhibition functions.6 In what follows, I criticize both the separatist and functional beauty approaches and then show how a moderate functionalist position can unite the intuition of a desirable concord between aesthetics and function and the intuition that spectacular aesthetic achievements may override functional faults. Before beginning a critique of the separatist and functionalist beauty positions, I need to outline some preliminary assumptions. The first is that the aesthetic experience of architecture is not only about the contemplation of visual form, but is also multisensory and immersive, involving the volumes, textures, and sounds that determine how a building feels as we move through it.7 Of course, we do experience many buildings only visually from the outside. In fact, the “spectacle” art museum controversy has arisen partly from the desire of some museum boards to have an iconic building whose external appearance will draw paying crowds. The importance of such issues as iconicity and symbolism suggests that our concept of aesthetic experience also needs to include a cognitive dimension. The cognitive aspect of aesthetic judgment seems especially appropriate to contemporary art museum architecture, which includes not only sculptural designs (Gehry, Zaha Hadid, Libeskind) but also works influenced by conceptual art (Elizabeth Diller and Ricardo Scofidio) or deconstruction (Peter Eisenman), whose formal and sensory satisfactions may be less important than the way they embody certain ideas. Like the concept of the aesthetic, the concept of function is not only unsettled but is also inflected by its application to architecture.8 Early modernists sometimes interpreted Louis Sullivan's “form follows function” to refer to “structural” function (form should reflect construction), at other times to refer to “practical” function (form should reflect human needs). But architecture theorists have also written of many other architectural functions: urban, environmental, social, ethical, symbolic, even aesthetic.9 The fact that there are many kinds of functions means that aesthetic and practical functions are almost always found intertwined with other functions, among which the symbolic and social are especially important for art museum architecture. Symbolic functions obviously concern architectural meanings, whether understood in terms of “exemplification,”“allusion,” or in some other way.10 Historically, one of the most important symbolic aims of art museum architecture has been to express the value of art itself. In the nineteenth century, this concern gave us those familiar classical temple forms with their grand stairways, spacious reception halls, and sumptuous materials, whereas today's “spectacle” museums try to send similar messages by means of radical shapes, dramatic massing, acres of glass, and unusual materials. Social functions in architecture concern the way buildings affect such things as our sense of well‐being, our sense of place, or the quality of human interactions within them. Arthur Danto has called attention to the way Steven Holl recently designed a stairwell in a faculty office building at New York University to invite chance meetings, thus creating “a remarkable aesthetic experience while solving a sociological problem.”11 When these kinds of social concerns inform specific practical functions in the design of schools, hospitals, or museums, spaces for teaching, healing, or exhibition can be transformed into something far richer than a neutral means to an end.12 This blending of social and practical functions also calls attention to their normative dimension, which has been so effectively described in different ways by Karsten Harries and Yuriko Saito.13 The normative dimension of functions is what makes us ready to criticize an otherwise aesthetically and symbolically exciting building for failing its practical or social purposes or, to criticize an otherwise functionally efficient building, for its sterility and lack of aesthetic vitality. With these general considerations in mind, we are in a better position to examine the separatist view that aesthetic and practical functions should be treated as simply parallel to each other. Roger Scruton and Edward Winters, reacting to extreme versions of “functionalism,” have claimed that a building's specific functions are irrelevant to its aesthetic appreciation.14 Scruton goes so far as to declare that the very idea of function is “fundamentally, and perhaps irremediably, obscure,” so that “all we can say … is that buildings have uses.”15 Moreover, both he and Winters believe that even if we could somehow get a clearer concept of function, it would not make any difference since a building's functions are liable to change with time.16 What remains most important for Scruton is “to find meaning in appearance itself,” so that “aesthetic considerations … must take precedence over all other factors.”17 But the separatist approach cannot do justice to the fact that most architects’ aesthetic choices take into consideration practical and other kinds of functions in the process of design, so that a particular set of functional concerns becomes embodied in architectural form. Major encyclopedic art museums, for example, are likely to have specialized spaces for a variety of practical functions, such as reception (entry halls), exhibition (galleries), or halls), whose architectural forms will have also been for social, symbolic, and aesthetic The specific practical functions of and for example, are dramatic such as for the or for the Art whose architectural forms not only aesthetic responses but also at the a of from the even as they symbolic similar of aesthetic qualities with social, and symbolic functions in the museum gallery the between the and as we move from the and architectural has to the less dramatic forms and spaces may be to a for a for art not that the architecture as in with design for the in New architectural forms should be aesthetically in ways that complement the art even as those forms a for and aesthetic I believe at this of the social, and aesthetic of gallery design when he neutral works of art as as spaces that make the building into a of In for example, one through its dramatic the of the for seem like an Libeskind's radical in Denver sometimes with the art for our go to the other extreme and an aesthetically less for than for The between the aesthetic and practical functions for gallery architecture can be to what has about the halls, such as in or Frank Gehry's in their designs to of an experience architecture by means of the as the are for the quality of their so the gallery designs make of natural to the experience of for example, Louis for the for the Steven walls for the Museum or for the museum in that give it a and In what to be an to this of aesthetic and practical concerns in gallery design, the Frank who so to the function of to in has as the idea that museum architecture should be and not with the the Bilbao museum's than a with a by and be a “spectacle‐space” to swallow almost in this is not the at also designed a number of for and and sculptural for contemporary and of the at Bilbao are are most of intrusive. In the design of the Bilbao Guggenheim, practical and social concerns in aesthetic and symbolic even if he not always a that I believe the of the functional in museum the of separatist and approaches that particular functions in aesthetic practical and other functional aims may as external to a have into their design, they to the to the way the external of a becomes of the of the would be as to the of a of architecture to the of practical and social functions in its forms as it would be to an extreme functionalist that in a should be by its The separatist position, the moderate functionalist approach I have been aesthetic judgment by the aesthetic function of forms from their practical and social Of course, a separatist to the idea of embodied functions, beginning with Scruton's and that since a building's practical functions may change with we are better them. from the that there is some “aesthetic that can be from a building, this the fact that through or the formal and sensory of many buildings may also change over so that involving practical functions are in this than formal a separatist that we may not be to whether the concord between the aesthetic and practical functions of a museum's art is to the design or to choices the of how to and so it is that a may make of an architectural designed for art or a designed for art, in most it is not to out the architectural choices from the One of the Denver for example, Libeskind's that the a of of the function as as they their When the Denver museum first in for example, by from the walls and to be from their on the walls by of on the When I the museum two these been by on the walls to to and on the to at a if one accepts these there remains a to the idea of embodied practical functions: the fact that many important art museums have been in and in which it would be to that we something about the of practical and aesthetic functions from the way the buildings the of many buildings for as art museums have been to make to But even in have been as at or even if one to a building into a museum at our judgment of the aesthetic qualities of the building in its would be by how the aesthetic and practical have been Of course, our attention in such would from the choices of the to the architectural choices of those for a museum in this particular At this a separatist or the by that aesthetic simply are about formal and sensory and the to make is the to responses to aesthetic from responses to like or to like and some be willing to the moderate functionalist that we can make the way practical functions have architectural but they would that these cognitive only concern and are irrelevant to aesthetic would that if we are to justify the of embodied functions in aesthetic we must make aesthetic only one of an judgment or the of aesthetic judgment in a way that these the of aesthetic responses only one of an judgment would aesthetic and practical functions they what we to is whether practical achievements or defects in a of architectural art can into the process of aesthetic itself. recently versions of to this by on our to than to works of art, and both in idea of I will on the position of Glenn Parsons and Allen since they not only make architecture a concern but also to Scruton's the concept of function by as the of can our to a building or an be by of its and the of can we the “proper” function of a building or an to the of on idea of of to that in the of how function us to different aesthetic qualities in of approach seems to show some for with architectural since spaces for and art have been for a so that one idea of forms to the of iconic art museums like Gehry's Bilbao or Libeskind's Denver addition and say that their or may be as an aesthetically or an aesthetically when it to the appearance of such it would seem to determine which forms are for an art museum for many other building so that are of value in at an aesthetic Parsons and Carlson's to Scruton's that the concept of function is also since they to be to determine a building's function” by to a concept on the function of an is some in the that it to a need in the in its In addition to some with the of it seems for architectural designs like art One is that Parsons and seem to architectural works as if they could have only a For example, in the controversy over the in as an but for its lack of formal in the as if the must be in that its “proper” function is to or the architecture critics must be in its “proper” function is to make a bold Parsons and that it may be so to the function in many that it will the of and social and even then it is what the of may But in the of building like art museums, we can to of the art that there is in fact function that has been by The functions of art museums have been since their in the of with and in the of art, and a for aesthetic Moreover, over priority among these functions has been going on since the beginning and of the for any one function as the function of an art museum seem some functions are obviously than for example, functions like or contemplation all depend on the functions of and architectural works like art museums a than like function” can the of both the separatist and functional beauty we are with an of how aesthetic art museums can include social, and symbolic functions and we need to show in what way a practical or can an aesthetic or in an architectural that I will first to idea of of a judgment of beauty for is a to the of the as in a of the and a judgment of beauty a concept of the that what the is to One of of a judgment of beauty concerns architecture, our to a that would be to our intuition could be to a building, “if only it not to be a When that such of beauty are not aesthetic some have how they could be aesthetic at the he on the of and But seems in this to of a that in a judgment of the concept of a not but the of the to of a the of a as a of which architectural forms can us but it not determine in any particular that would the needs of have interpreted of a or as external and that we first take of an as an of its found it to its we then it as have interpreted of beauty as an of a judgment on in the of to a judgment on a in of these that a building is of a certain us to expect that it will the functions of that if it we may go on to its formal But when a building its functions we may find our in its to the building's the and the of of beauty do make function to aesthetic by a both to the separatist position we are to What we need is an of of beauty that can show how function can be a of the process of aesthetic Of the of idea of beauty that for a I find most that of in on and For aesthetic judgment in general attention to all the of an as these are in the of and In a judgment of this of our experience is on the form, but in a judgment of such as aesthetic or the are into an … of the on we an as a the that make it a of its are to be aesthetically aesthetic In of an practical purposes do not judgment from the or get with in an way but also are an of a process of are the appropriate of what I have to as embodied as must practical and other functions with their aesthetic so those who the building must to and other or, in to the aesthetic function” of the Of course, by of or into the of and such are and can to But the of a concept such as beauty is to make for a of aesthetic judgment that the of like social, and symbolic are aesthetic in the sense that they are of are they that directly a general can be into a aesthetic judgment of architecture so as function is in to be in with the other it seems to is what when we take in the way the inward walls of Steven for addition to the Museum are at one and the forms and of natural who is otherwise to concept of that to the specific functions of building into aesthetic may find I believe is the problem of the of seems for any approach to aesthetic judgment that a cognitive Moreover, the of a to the is than for by the of a of beauty that as to take into than those that an simply “a good of its I would that we should not the of aesthetic, and other functions of a particular museum in a way that it as an of the general building art but always move to the appropriate of The kinds of architectural forms that would the function of a museum like the in with its of are likely to be different from the forms appropriate to the New Museum of Art in New York or to a museum such as the Museum in The need to take into the of functions appropriate to different kinds of art museums means that the of beauty I to be by the that “all are preliminary on an of beauty is a there may be in the way people in the aesthetic judgment of a of architecture, one they cannot they cannot give the specific practical functions of a building in an aesthetic This to may seem a especially since at the very of of seems to the out from not only an view of practical functions in aesthetic judgment but even from the and that a through of an or by from such a as if it is to out that when we are of a building's we are when we a strange or are likely to to a of architecture as form. But other that even when we what the function is we may from while also seems to with the idea of could be as the of aesthetic and practical functions, a to the social, and symbolic functions of a of architecture whereas I have that the idea of beauty that a cannot such functions have ways to as with idea of I in the way it a of the other intuition about works of architecture that I at the beginning of this and to which we must our I there that our intuition that aesthetic qualities and practical functions should be in architecture, we seem to have an natural intuition that some buildings are aesthetically so that we may their appearance their practical One way of this other intuition is by to the between architecture and building, by the art is a is architecture. architecture only to buildings designed with a view to aesthetic a similar in some of on architecture, that as of the human is not “a so functional is not on the he designed for in he that in of its satisfying and practical it what he called In these seems to the architecture building to an even than “aesthetic the has interpreted the building architecture as one between and architecture, for which he the of the and the of one of the we have the a and to … at at the other we have the which and us with buildings or are by who as with their to a of practical and aesthetic on the other are designed by who as the of who are us the most spectacular of The problem with the is that most have at some aesthetic and most or works of have some so that the to be an as a the of architecture and building may have some for or to it as for practical functions in the aesthetic judgment of works would simply make practical functions irrelevant by Gehry's or Libeskind's Denver Museum addition may so us by their and that we may be to some of their practical faults. But that is very different from that their specific function of art is irrelevant to in the of “spectacle” or architecture, we need to the that “all are when we a of aesthetic, symbolic, social, and practical as for aesthetic of course, the of works like the the or which we as of architectural art that can be simply as of even they may be for some even their I believe it will us how a functional in a of architecture can to an aesthetic judgment and how a similar functional in a different may not in an judgment by the problem of the between defects and aesthetic For many like functional have been irrelevant or at to from aesthetic At the other pole, the position sometimes called that a in a of art is always an aesthetic and should to a aesthetic What calls “moderate both that an may in certain an aesthetic In a for example, a may try to the that a with a but the is something with the of the has not been designed on its As this of aesthetic to a of art is the of an of many of the not simply the of a or But as it is to at an aesthetic in some it is also to at an in other in which a when all things are defects that are by its other such as formal approach to and aesthetics the of of beauty that I to a similar of practical and formal in an aesthetic is I have called perspective on architecture “moderate “moderate The moderate functionalist not the in aesthetic and practical functions as but the moderate functionalist “functional beauty” in that the aesthetic of an must be in terms of how they a “proper” a moderate functionalist a judgment about a of architecture that is aesthetically exciting but it will be the to embody its practical functions the of its formal and other aesthetic the moderate functionalist is also ready to that a of architecture to all things are defects that are by its other such as formal architecture, of course, will into the of what called the but buildings are less important or of for their aesthetic in aesthetic with practical and other functions than is the spectacular building that so us with that we what it to as a in a or remains a the aesthetic so a practical and social in a of architecture remains a practical and social even when we that it is by aesthetic In I to to the two of spectacular art museum architecture with which I The sculptural and the of its are not only aesthetically but also the symbolic function of important for our the aesthetically of the of its for art are appropriate to the kinds of art each is to In the Bilbao museum's aesthetic and symbolic could be as for the practical of a of its gallery In the of Libeskind's Denver on the other a that is aesthetically and symbolically as a the walls of of its with their exhibition function in ways that have many aesthetic judgment of the there are a the museum's and walls complement particular contemporary in many other the architecture on the art in Libeskind's Museum in and symbolic that give meaning to its aesthetic and for its functional as an exhibition the Denver symbolic and aesthetic not seem to for its practical As these aesthetic of the “moderate will not only kinds of functions into the process of aesthetic but there will also be in the that may be to each the of such not into but to about how a museum's functions have been in the In can an appropriate aesthetic judgment practical functions as irrelevant in the museum's aesthetic as the separatist approach would on the other can one that there is a “proper” function that should be the in the aesthetic judgment of a museum In this I one can both our intuition of a desirable concord between the aesthetic and practical of works of architecture and our intuition that some works are aesthetically so that we may their practical faults.
Part of the SETI Institute's 42-telescope Allen Telescope Array (ATA) in California. (SETI Institute) Part of the SETI Institute's 42-telescope Allen Telescope Array (ATA) in California. (SETI Institute) The first Search for Extra—Terrestrial Intelligence (SETI) project of the modern era was done by Frank Drake in the spring of 1960, using the Green Bank 26 m telescope. He was looking for narrow—band radio emission from two nearby stars, t Ceti and ε Eri, over a frequency range of 400 kHz near the H i line. Since then there have been six major and many minor searches, made both on specific targets and also over the entire sky. The searches have extended to the optical and infrared, and to search for artefacts in the solar system and beyond. There have also been more than a thousand papers in the scientific press. The searches have all come up negative. What does this mean? Can future searches extend in a significant way the present area of the “ETI phase space” that has been searched for the existence of extraterrestrial intelligences (ETIs)? This article will briefly describe some of the component parts of SETI and put forward the case that SETI does indeed have an exciting future. SETI has two main aims. There is the expanding exploration of that phase space, always with the possibility of “contact” and the leap forward in our understanding of life in the universe and in many other fields of science and culture that would result. But SETI also addresses the future of humankind, looking for other civilizations that have trodden this path before us. If we find them, then we will know there is a possible way forward. If a particular SETI search comes up with a negative result, then we know that our future may not include the path that that search would have revealed. SETI activity has other components. It involves studies of: how evolution leads from the origin of life to intelligence; the rise and nature of technological civilizations; the problems of communications with fundamentally different entities; the possibilities of interstellar travel. It provides a logical extension to the growing field of astrobiology. Like all high—tech work, it has spin—offs, such as the Berkeley BOINC system of grid computing, originally designed to deal with the flood of SETI data from the Arecibo telescope with the SETI@home project, and which is now used in many fields, including medicine, molecular biology and climatology. And SETI provides a powerful forum for engaging with the public on the nature of scientific studies, using a subject in which the public is already interested. We know very little for sure. We know from our own example that technological civilizations can arise and persist for thousands of years, and send both “leakage” and deliberate radio and optical signals of their existence out to the galaxy. We know that our civilization arose in the last 10% of the age of the Earth before the increase in the Sun's output will render the surface of the Earth uninhabitable. We know that no ETI has left evidence of its existence in any of the searches that have been made, on the Earth, in the solar system, or further afield. Our existence means that other civilizations could exist, but gives no indication of their probability. Our recent knowledge of extraterrestrial planets suggests that Earths hospitable to life are common. However, since we do not know how life started, we do not know if life is common, rare, or if the Earth is the single case. Within the next decades the study of the atmospheres of Earth—like planets may resolve this point. However, we next do not know the probability that once life has started whether it then evolves to a technological civilization. We cannot say that evolution is bound to produce intelligence, and we are unable to predict the nature of other technological civilizations, or how long such civilizations exist. Civilizations thousands, millions, or billions of years older than ours could be of a very different nature to our own. However, the late arrival of intelligence on Earth is most compatible with an average time for the arrival of intelligence being much longer than the lifetime of stars, and thus with us being alone. But this is only a probabilistic pointer, not a proof. The view shows the first LOFAR station to be built in the UK at STFC's Chilbolton Observatory, with the Low Band Array in the foreground. Unlike conventional radio telescopes, there are no moving parts, but steering of the telescope is done in software. When completed, LOFAR will consist of more than 5000 separate antennas spread in ‘stations’ all over Europe. The project is based in the Netherlands where the core of the array is located. (STFC/SEPnet) The view shows the first LOFAR station to be built in the UK at STFC's Chilbolton Observatory, with the Low Band Array in the foreground. Unlike conventional radio telescopes, there are no moving parts, but steering of the telescope is done in software. When completed, LOFAR will consist of more than 5000 separate antennas spread in ‘stations’ all over Europe. The project is based in the Netherlands where the core of the array is located. (STFC/SEPnet) The lack of evidence of ETI is known as the Fermi Paradox. Once a civilization gets to our stage, it would only be a short time before it could build Von Neuman probes — autonomous self—replicating space probes — whereby every planet in our galaxy could be visited within a few tens of millions of years. The simplest explanation for the fact that we do not see such probes here, and that none of our searches have found signs of ETI, is that we are alone. However, there is no lack of credible alternative explanations of how the existence and even widespread existence of ETI would be compatible with the negative search results. These searches have as yet only explored a very small fraction of ETI phase space. So although there is some indication that we are alone, all we can presently say is that it is possible that ETI is out there, but we cannot with any degree of certainty predict how often ETI arises, or what their natures or lifetimes would be. The most common way of looking for ETI is to look for narrow—band radio emission. Our civilization emits such radiation from the 1 Hz wide carrier beam of analogue TV stations through to the kilohertz wide emissions of such things as airport radars. ETI may also emit such leakage radiation, although present searches are only sensitive to much more powerful radiation than we presently emit. Narrow—band radio waves are also the cheapest and most efficient method of interstellar communication that we know of, and so may be ETIs' way of communication, and even of signalling their existence to us (“beacons”). The narrow—band signature can also be distinguished from natural sources, even rare natural narrow—band ones such as masers. The Harvard and Argentinian searches with 26 m telescopes covered the entire sky, and the Arecibo “piggy—back” survey covered some 25% of the sky. But these have integration times of only a minute or so. The SETI Institute among others has done many longer integrations on individual targets such as nearby stars. Searches have become more powerful as receivers, electronics and data handling and analysis software improve, as for example in the billion 1 Hz spectral resolution channels of the 42—telescope Allen Telescope Array (ATA). The most recent surveys are now a trillion times more capable than Drake's 1960 observations. Following the recent development of high—powered lasers, which in theory could be matched with telescopes to outshine the Sun in nanosecond pulses, searches have started to look for such ETI signals in the optical. Pointed observations at Berkeley and Lick and an all—sky survey at Harvard are now looking for such nanosecond pulses. Again these are distinguishable from natural sources. If an ETI were using one of our most powerful lasers and a 10 m telescope, these searches would pick them up from hundreds of light—years away. More exotic radiation sources, such as the neutrinos from supernova SN1987A, are also investigated for signs of an artificial nature. The most famous such search was in 1967 when the Cambridge pulsar discovery team checked that the pulses had no sign of orbital motion. Different searches have different aims, usually based on some sort of premise of the nature of ETIs. The most obvious choice is of nearby long—lived stars, where ETIs on planets have had time to evolve. Such searches range from Drake's observation of two such stars in 1960, to the million stars planned for ATA. Since stars can differ in ages by billions of years, and ETIs take an unknown time to emerge, a search of a million stars gives a chance of picking up an ETI radiating for a thousand years, which may be a reasonable estimate of the time until an ETI changes into a fundamentally different mode. Then there are the all—sky surveys and surveys of areas of the sky, such as the galactic centre, where no presumption is made of where ETI is — on or off planets, near or far. These necessarily have shorter integrations per pointing, so are sensitive to rarer but brighter sources. The extreme of this is surveys of other galaxies, looking for extremely bright sources, but sources so rare that there is not one in our own Milky Way. There are also specialized searches. A recent proposal is for a search on the ecliptic plane, where an ETI would have been aware for a long time, using the radial velocity and transit planet detection methods, that there is an Earth in orbit around the Sun. Perhaps this would prompt them to signal to us. Searches have also been done looking for artefacts of an ETI civilization. The most famous of these are Dyson spheres, where an ETI surrounds a star with solar panels, probably on many discrete mounts, to tap a significant fraction of the star's energy. The outsides of these panels will be cool, shining in the infrared. Each new infrared catalogue that comes out is scanned for objects of strange non—natural looking colours. There have been searches for strange colours in the asteroid belt objects which might indicate an artificial nature, and for objects in the unstable Earth—Moon L4 and L5 Lagrangian points. There are notoriously many “sightings” of UFOs, which all have either been explained or have not contained enough information to determine their natures. The most interesting ongoing scientific investigation is the Norwegian Hessdalen Valley Project where there have been repeated sightings. The main limit on these searches is funding. There are almost no public funds. Very little sustained work is done outside the US, and within the US the main work is done through private funding and the efforts of determined individuals at Berkeley and Harvard. The SETI Institute, which grew out of the NASA work of the 1970s and 80s, is privately funded and the Berkeley and Harvard projects are done from within radio astronomy and electronics groups with university funding and private support. Outside radio and optical searches there is almost no concerted academic work on the other areas of ETI phase space such as solar system searches or catalogue analysis. Theoretical work depends on the intermittent interest of individuals. There is a lack of resources to fund fresh blood. Over the past 50 years there have been hundreds of papers describing the capabilities of searches and suggesting new methods. There have been as many speculating about the existence, origins, lifetimes and natures of ETIs, about composing and decoding messages, the prospects for interstellar travel and many allied matters. There has been much cross—fertilization with other fields including biology, philosophy, spaceship propulsion, linguistics and planetary science. Is intelligence a convergent property, etc? Some pointers to this extensive body of literature are given in the “Further reading”. An important field for SETI is the evolution of intelligence. Once life is started, does it then always evolve to intelligence? Intelligence seems such a useful attribute that evolution would home in on it, but for two billion years bacteria reigned alone. Since then there have been millions of species on Earth, out of which only one, us, has evolved advanced technology. Were we inevitable? Is evolution convergent? And then there is the “Man from Mars” problem, as it is known in linguistic studies. Can there be ways of communication that are so fundamentally different from our own that the message may be incomprehensible? Concepts such as “signs” and “signifiers” may not be present. How would a communication system based on smells be coded into a radio message? A standing controversy is whether it is dangerous to send out signals. In fact any advanced ETI would probably know about us already from our various radio emissions of the past six decades, or from visible signs such as the existence of our cities over the past four thousand years. And because we do not know about the nature of any ETI, a signal might either provoke or forestall an attack by any ill—intentioned ETI. So there is no reason not to transmit. But in any case there is probably presently little point, as signalling for thousands of years would be needed to give the class of ETIs not much more advanced than us a reasonable chance to pick us up. (Only such ETIs would not necessarily know all about us already.) In studying the future of humankind, we already know that certain classes of ETI, those that our searches would have picked up, are not common. How much does that tell us about the long—term evolution of civilizations like our own? Will we become a civilization that SETI searches could detect? Will we survive the bottlenecks of the near future: global warming, nuclear war, biological terrorism, grey goo, a catastrophic meteorite strike, the rise of the machines? In the more distant future, will we establish self—sustaining colonies off the Earth that will lessen our vulnerability? In the very distant future, will we become a race that can persist for a million or a billion years? SETI provides an avenue, the only observational avenue presently available to us, for exploring these puzzling questions. An example of how SETI thinks about our own future is the “Great Filter”. Taking from the Fermi Paradox that advanced ETIs are not common, Hanson (1998) pointed out that in the progress from star formation to such ETIs there must be a limiting pinch point. If this is behind us, then we are one of the extremely rare cases to have got this far, and our future prospects are not limited. But if it is in front of us, then we will very probably be extinguished. Paradoxically, discovery of ETIs like us, but not too advanced, would be bad news, as then it must be easy to get as far as us, and the Great Filter must be in front, and quite close. If we detect an ETI, what would happen next? First of all, there is the getting out of the news, and present SETI searchers subscribe to the International Academy of Astronautics SETI Permanent Study Group's “Post—detection Protocol”, which basically says “be sure, have it confirmed, and then spread the news widely”. No signal should be sent back until international agreement has been reached. In practice, the experience of search groups is that, when investigating ambiguous signals, the news can leak out in an uncontrollable way. What happens next would depend on the origin and nature of the signal. A solar system detection would have its own possibilities and problems. The result of a radio or optical detection of a distant source would depend on its nature. A continuous narrow—band signal which simply says “I am artificial” would revolutionize the scientific field and trigger funds for a great search for more details. Does it show signs of orbital motion? Is it associated with a star? It would also trigger public and philosophical interest. It is generally thought that the public would be intensely interested, but would not overreact. However, if there were to be some sort of code seen in the signal, then as well as the scientifically fascinating cryptological and linguistic tasks of finding out what the message is, the public interest would be overwhelming. Coming from an advanced civilization, does the message tell us how to behave, explain about religions, contain a cure for cancer? Is there some sort of danger in the message? If we respond, how do we have a conversation that may involve time lags of centuries? Astronomers would be interacting with the community in ways that are difficult to envision. Given the negative results so far, is it worth going on? We do not know what ETIs are like, so we cannot say how large the phase space of possible ETIs is and thus we neither know if we are looking in the best way nor what our chances of success are. Many SETI searchers remain optimistic. The quotation from Cocconi and Morrison's 1959 foundational paper that “The probability of success is difficult to estimate; but if we never search, the chance of success is zero” has many supporters. However, without knowing the nature of ETIs we cannot estimate by how much we improve our chances by any particular SETI search. Within the next decade we should be able to rule out (or discover) leakage radiation similar to our own from nearby habitable Earths — but the chance of hitting the perhaps thousand—year window for such radiation for a planet millions or billions older or younger than us must be very small. The author's personal opinion is that although we cannot know what our chances are it would be a failure of nerve not to go on looking, as long as each new search does cover significant new phase space at a reasonably modest cost. Planned radio searches will get more powerful, from the privately funded ATA array partly dedicated to SETI searches, to the use of new telescopes such as the European LOw Frequency ARray (LOFAR), for which the author is PI on a SETI Pilot Programme, and the South African 64—dish MeerKAT array, which has recently announced that it wishes to “explore further the potential for SETI”. And there is the giant Square Kilometre Array on which funding are to advanced receivers, electronics and software we are for giant forward. A major present is in the electronics and and so an in with and telescope that to and all—sky with in the other of searches, such as the optical new solar system searches of new and into the next decade is with possibilities to extend the ETI phase space we are by the almost lack of public funding. When to the public about SETI and tell them that almost none of their astronomy to SETI are that such an interesting field is being If the panels of the astronomy funding were to to fund SETI at a of one of one of their SETI would be and much more powerful and searches could be would be an thought for us all — that we were the search and in this into the unknown the race is looking
INTRODUCTION We, the generation living in the early years of the 21st century, occupy a special position in human history, in that we have witnessed unprecedented and unparalleled growth in the understanding and knowledge about the world around us and life on this planet. While we bask in that glory, let us not forget that there are some important and large questions that remain embarrassingly unanswered. The most conspicuous of those questions is one that is central to the field of psychiatry - “What is the mind?” Nevertheless, psychiatrists have brazenly avoided or ignored this question due to a learned lack of enthusiasm, given the historical inability to achieve a consensus about anything pertaining to the mind. Not to mention the inevitable criticism and/or possible ostracism that relentlessly pursues anyone who takes a stand on this controversial issue. Psychiatrists did not just want to open that can of worms! We simply hoped that if we managed to keep the can closed, the worms would suffocate and die and we would never have to face that uncomfortable question again. We believed that just like we managed to evade the exact definition of mental illness, we would be similarly successful in evading the definition of the mind. However, in the last several decades, human life has transformed so much that we are now faced with a relatively new concept - mental health, which too remains to be defined. The list keeps growing and our silence has been deafening. While our understanding of the human brain, human behaviour, and neurosciences has grown exponentially, the task of describing or defining the mind has also become increasingly difficult. Our wilful indifference or tactical retreat from confronting these tough questions is not helping us, one bit. Increasingly, we are educating ourselves with an explanation that any definition of mind or mental health is not even a possibility, let alone plausibility. Let me highlight the importance of this issue by discussing the well-known, controversial, yet insightful Rosenhan experiment. THE ROSENHAN EXPERIMENT In 1973, American psychologist David L. Rosenhan published the findings of his controversial study, ‘On being sane in insane places’ in the journal Science, stirring up a lot of reactions and criticisms among the psychiatric community.[1] It was a two-part experiment exploring the consistency and validity of traditional methods of psychiatric diagnoses. For the first experiment, Rosenhan arranged a group of 8 normal individuals called ‘pseudopatients’ who were known to have no psychological or psychiatric pathology. They included a psychology graduate student, 3 psychologists, a pediatrician, a psychiatrist, a painter and a housewife. Three of them were women and five of them men. Rosenhan was one among them. These pseudopatients appeared at 12 different psychiatric hospitals (11 university or state hospitals and 1 private hospital), reporting a false complaint of repeatedly hearing something such as “thud”, or “hollow” or “empty” and gaining secret admission. They used pseudonyms (false names) to feign their real identity. However, other than this fabricated complaint of auditory hallucination, no other and as would Rosenhan this experiment to if psychiatrists the pseudopatients with one fabricated as these were with the one who appeared at the private who was with of them were with and and at and to the study, these pseudopatients of the complaint admission. 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In this thesis, we provide contributions to signature schemes and identi cation schemes in four di erent ways.\nFirst, we make contributions to universal designated veri er signatures. We propose the notion of a one-time universal designated veri er signature such that the number of veri ers verifying the signature is controlled by the signer. We also propose the notion of a universal designated veri er signature with threshold-signers such that the privacy and anonymity of the signer can be achieved.\nSecond, we propose a new notion called "policy-controlled signatures". In this notion, a policy-controlled signature can be veri ed by a veri er that satis es a policy assigned by a signer. We provide two extensions to this notion, which are "universal policy-controlled signatures" and "multi-level controlled signatures". Universal policy-controlled signatures allow a party called "a policy signer" to apply a policy on a signature on a particular message such that only a veri er that satis es this policy can verify this policy-controlled signature. In practice, some policies can be simply represented by a level of the security, for example, "POLICY= more than the fth level of security". From the above idea, a de nition of multi-level controlled signatures is introduced. It allows a signer to eliminate the unnecessary chain of attributes in the policy and simply assign the level of security as a policy instead. Hence, the size of the policy remains constant.\nNext, a new notion called "fair multi-signatures" is proposed. A multi-signature allows a group of parties to engage in an interactive protocol in order to generate a joint signature on an agreement. If all the signers follow the protocol honestly, then a multi-signature is generated and distributed fairly. However, if a dishonest signer refuses to complete his part in the protocol, but he has already obtained the other parties' contributions, then the honest signers cannot obtain a multi-signature and yet the dishonest signer can generate a multi-signature. Our notion of fair multisignatures ensures that if the protocol is completed, then every signer involved in the signing protocol can output a multi-signature. Meanwhile, if the protocol is not completed, then none of the signers involved in the signing protocol can output a multi-signature.\nFinally, in modern communications, the public becomes aware of privacy issues. Some identi cation systems provide privacy for users, especially those that are based on zero knowledge proof. However, a malicious user may take advantage of privacy to deny his malicious acts. Hence, we propose a new notion called "escrowed deniable identi cation schemes". In this notion, a trusted party is introduced to act as a transaction opener such that it can generate evidence of the conversation from the deniable transcript generated during the interaction between a prover and a veri er. In an identi cation scheme, the major concern about security is impersonation. The strongest type of attack against identi cation schemes is the reset attack. In this thesis, we provide an identity-based identi cation scheme secure against reset attack. We also provide proof of our scheme which is secure against reset attack in the standard model.
Memorizing Mathematics: The Failure to Apply Mathematical Axioms Within Restrictive Models Rony Patel Rutgers University Jennifer Jacobs Rutgers University Rochel Gelman Rutgers University Abstract: Arithmetic, along with all mathematics, is built on axioms. Mathematical education, however, favors mathematical models or algorithms without appeal to the axioms they depend on. Our series of studies demonstrate adult subjects’ inability to take advantage of the knowledge embodied in arithmetic axioms. It is likely that students’ ability to master generative proofs is related to the reliance on restrictive models. Our first set of studies focused on subjects’ ability to apply the addition-rule (mutually exclusive events) and the multiplication-rule (independent events) with multiple rational number representations (percentages, decimals, fractions, etc.). A second set of studies tested the understanding of group theory properties, exploiting the effect of the order of numbers (commutativity) and the effect of the digit zero (additive identity) on the long multiplication model (LMM). All studies conducted revealed participants ability to accurately perform arithmetic on chosen representation, but poor performance on choosing representation.
Open access
Mathematics Education and Teaching Techniques
Cognitive and developmental aspects of mathematical skills
Zeev Dvir, Dan Gutfreund, Guy N. Rothblum, Salil Vadhan
Abstract: We investigate the complexity of the following computational problem: Polynomial Entropy Approximation (PEA): Given a low-degree polynomial mapping p: Fn → Fm, where F is a finite field, approximate the output entropy H(p(Un)), where Un is the uniform distribution on Fn and H may be any of several entropy measures. We show: • Approximating the Shannon entropy of degree 3 polynomials p: Fn 2 → Fm 2 over F2 to within an additive constant (or even n.9) is complete for SZKPL, the class of problems having statistical zero-knowledge proofs where the honest verifier and its simulator are computable in logarithmic space. (SZKPL contains most of the natural problems known to be in the full class SZKP.) • For prime fields F = F2 and homogeneous quadratic polynomials p: Fn → Fm, there is a probabilistic polynomial-time algorithm that distinguishes the case that p(Un) has entropy smaller than k from the case that p(Un) has min-entropy (or even Renyi entropy) greater than (2 + o(1))k. • For degree d polynomials p: Fn 2 → Fm 2, there is a polynomial-time algorithm that distinguishes the case that p(Un) has max-entropy smaller than k (where the max-entropy of a random variable is the logarithm of its support size) from the case that p(Un) has max-entropy at least (1 + o(1)) · kd (for fixed d and large k).
Smartmeters report the current electricity consumption over the internet back to their energy providers. Finely-sampled power consumption enables the energy provider to learn the habits of the customer's household in which the smart meter is installed. This paper presents a protocol which preserves customer privacy but also allows the detection of unregistered smart meters and prevents spamming and replay attacks. A trusted-third-party is not needed. This protocol, whose security proof relies on the strong RSA assumption and the random oracle model, is based on zero-knowledge techniques. The protocol has been implemented on different hardware platforms and benchmark results are given.
Open access
Cryptography and Data Security
Smart Grid Security and Resilience
Physical Unclonable Functions (PUFs) and Hardware Security
We propose a coin-flip protocol which yields a string of strong, random coins and is fully simulatable against poly-sized quantum adversaries on both sides. It can be implemented with quantum-computational security without any set-up assumptions, since our construction only assumes mixed commitment schemes which we show how to construct in the given setting. We then show that the interactive generation of random coins at the beginning or during outer protocols allows for quantum-secure realizations of classical schemes, again without any set-up assumptions. As example applications we discuss quantum zero-knowledge proofs of knowledge and quantum-secure two-party function evaluation. Both applications assume only fully simulatable coin-flipping and mixed commitments. Since our framework allows to construct fully simulatable coin-flipping from mixed commitments, this in particular shows that mixed commitments are complete for quantum-secure two-party function evaluation. This seems to be the first completeness result for quantum-secure two-party function evaluation from a generic assumption.
David Bernhard, Véronique Cortier, Olivier Pereira, Ben Smyth · 5 authors
Abstract. Recent results show that the current implementation of He-lios, a practical e-voting protocol, does not ensure independence of the cast votes, and demonstrate the impact of this lack of independence on vote privacy. Some simple fixes seem to be available and security of the revised scheme has been studied with respect to symbolic models. In this paper we study the security of Helios using computational models. Our first contribution is a model for the property known as ballot privacy that generalizes and extends several existing ones. Using this model, we investigate an abstract voting scheme (of which the revised Helios is an instantiation) built from an arbitrary encryp-tion scheme with certain functional properties. We prove, generically, that whenever this encryption scheme falls in the class of voting-friendly schemes that we define, the resulting voting scheme provably satisfies ballot privacy. We explain how our general result yields cryptographic security guaran-tees for the revised version of Helios (albeit from non-standard assump-tions). Furthermore, we show (by giving two distinct constructions) that it is possible to construct voting-friendly encryption, and therefore voting schemes, using only standard cryptographic tools. We detail an instan-tiation based on ElGamal encryption and Fiat-Shamir non-interactive zero-knowledge proofs that closely resembles Helios and which provably satisfies ballot privacy. 1
Ivan Damgård, Jakob Funder, Jesper Buus Nielsen, Louis Salvail
Attacks on classical cryptographic protocols are usually modeled by allowing an adversary to ask queries from an oracle. Security is then defined by requiring that as long as the queries satisfy some constraint, there is some problem the adversary cannot solve, such as compute a certain piece of information. In this paper, we introduce a fundamentally new model of quantum attacks on classical cryptographic protocols, where the adversary is allowed to ask several classical queries in quantum superposition. This is a strictly stronger attack than the standard one, and we consider the security of several primitives in this model. We show that a secret-sharing scheme that is secure with threshold $t$ in the standard model is secure against superposition attacks if and only if the threshold is lowered to $t/2$. We use this result to give zero-knowledge proofs for all of NP in the common reference string model. While our protocol is classical, it is sound against a cheating unbounded quantum prover and computational zero-knowledge even if the verifier is allowed a superposition attack. Finally, we consider multiparty computation and show that for the most general type of attack, simulation based security is not possible. However, putting a natural constraint on the adversary, we show a non-trivial example of a protocol that can indeed be simulated.
We present new candidates for quantum-resistant public-key cryptosystems based on the conjectured difficulty of finding isogenies between supersingular elliptic curves. The main technical idea in our scheme is that we transmit the images of torsion bases under the isogeny in order to allow the parties to construct a shared commutative square despite the noncommutativity of the endomorphism ring. Our work is motivated by the recent development of a subexponential-time quantum algorithm for constructing isogenies between ordinary elliptic curves. In the supersingular case, by contrast, the fastest known quantum attack remains exponential, since the noncommutativity of the endomorphism ring means that the approach used in the ordinary case does not apply. We give a precise formulation of the necessary computational assumptions along with a discussion of their validity, and prove the security of our protocols under these assumptions. In addition, we present implementation results showing that our protocols are multiple orders of magnitude faster than previous isogeny-based cryptosystems over ordinary curves. This paper is an extended version of [19]. We add a new zero-knowledge identification scheme, and detailed security proofs for the protocols. We also present a new, asymptotically faster, algorithm for key generation, a thorough study of its optimization, and new experimental data.