This thesis describes an electronic voting system based on Damg\\aa rd, Jurik and Nielsen's generalization of Paillier's probabilistic public key system. A threshold variant of this homomorphic cryptosystem is used to provide universally verifiable elections, where zero-knowledge proofs are used for proving correctness of votes.\n\nUsing this cryptosystem, an electronic voting system that supports voting for 1 out of $L$ candidates is described. Two types of encoding may be used to prove the validity of the votes. The number of proofs needed using normal encoding is linear in $L$, while the number of proofs needed using binary encoding is logarithmic in $L$. It is shown how to extend the system to allow casting a vote for $t$ out of $L$ candidates. This method may easily be used to carry out elections with weighted votes without any added complexity to the system.\n\nThe system is shown to satisfy the requirements for elections at The Norwegian University of Science and Technology (NTNU). A fully functional implementation of the electronic voting system as a distributed system, using Java Remote Method Invocation, is presented. The implementation is used to analyze the feasibility of using this voting system for future elections at NTNU. The implementation is tested using various keylengths and various election parameters. With a keylength of 1024 bits, the simulated time for verification of complex elections is small enough to be considered universally verifiable.
Abstract The notion of non-interactive zero-knowledge (NIZK) is of fundamental importance incryptography. Despite the vast attention the concept of NIZK has attracted since its introduction, one question has remained very resistant: Is it possible to construct NIZK schemesfor any NP-language with statistical or even perfect ZK? Groth, Ostrovsky and Sahai recently positively answers to the question by presenting a couple of elegant constructions. However,their schemes pose a limitation on the length of the proof statement to achieve adaptive soundness against dishonest provers who may choose the target statement depending on thecommon reference string (CRS). In this work, we first present a very simple and efficient adaptively-sound perfect NIZKargument system for any NP-language. Besides being the first adaptively-sound statistical NIZK argument for all NP that does not pose any restriction on the statements to be proven,it enjoys a number of additional desirable properties: it allows to re-use the CRS, it can handle arithmetic circuits, and the CRS can be set-up very efficiently without the need foran honest party. We then show an application of our techniques in constructing efficient NIZK schemes for proving arithmetic relations among committed secrets, whereas previousmethods required expensive generic NP-reductions. The security of the proposed schemes is based on a strong non-standard assumption,an extended version of the so-called Knowledge-of-Exponent Assumption (KEA) over bilinear groups. We give some justification for using such an assumption by showing that thecommonly-used approach for proving NIZK arguments sound does not allow for adaptivelysound statistical NIZK arguments (unless NP ae P/poly). Furthermore, we show that theassumption used in our construction holds with respect to generic adversaries that do not exploit the specific representation of the group elements. We also discuss how to avoid thenon-standard assumption in a pre-processing model.
The Laplace equation and the related p-Laplace equation are closely associated with Sobolev spaces. During the last 15 years people have been exploring the possibility of solving partial differential equations in general metric spaces by generalizing the concept of Sobolev spaces. One such generalization is the Newtonian space where one uses upper gradients to compensate for the lack of a derivative. All papers on this topic are written for an audience of fellow researchers and people with graduate level mathematical skills. In this thesis we give an introduction to the Newtonian spaces accessible also for senior undergraduate students with only basic knowledge of functional analysis. We also give an introduction to the tools needed to deal with the Newtonian spaces. This includes measure theory and curves in general metric spaces. Many of the properties of ordinary Sobolev spaces also apply in the generalized setting of the Newtonian spaces. This thesis includes proofs of the fact that the Newtonian spaces are Banach spaces and that under mild additional assumptions Lipschitz functions are dense there. To make them more accessible, the proofs have been extended with comments and details previously omitted. Examples are given to illustrate new concepts. This thesis also includes my own result on the capacity associated with Newtonian spaces. This is the theorem that if a set has p-capacity zero, then the capacity of that set is zero for all smaller values of p.
Recent studies argue that traditional voting systems do not encourage increased voter participation due to constraints in time, location, accuracy, and, accessibility. To ensure the rights of a democratic society and to enhance and secure the voting rights of citizens by surpassing all the limitations of the traditional voting system, the development of an electronic voting system is an attractive solution. Research on secure electronic voting systems has been conducted for at least the past two decades. We propose to develop an electronic voting system, called the Rochester Institute of Technology Student Government Election System (SGEES) based on Damgard et al. This voting scheme will use efficient honest-verifier zero-knowledge, which, unlike previous election schemes, are both easy to compute and to verify for both voters and authorities. Our proposed electronic voting system will allow convenient and confident voting while maintaining the accuracy of election results. This project will address the security requirements for electronic voting over the Internet, including privacy, completeness, soundness, receipt-freeness, and universal verifiability. In particular, we will research the feasibility of the voting scheme and protocols by studying three related cryptographical theories: homomorphic encryption, efficient honest-verifier zero-knowledge proofs, and threshold decryption cryptosystem.
Serge Abiteboul, Bogdan Cautis, Amos Fiat, T. Milo
The common assumption about digital signatures is that they disallow any kind of modification on signed data. However, a more flexible approach is often needed and has been advocated lately, one in which some restricted modifications may still occur, without invalidating the data. This is made possible by offering signatures which are homomorphic with respect to some operation on the message domain. Starting from the signature(s) of some data instance(s), computed by the data owner, anybody else can derive the signature corresponding to a new data instance, if obtained only via some accepted operation from the previous one(s). More, updated signatures should be indistinguishable from the ones computed by the data owner and this updating step should be applicable as many times as needed. This paper deals with the signing of insert-only collections, in which element insertions are accepted but no removals should occur. Newly inserted elements do not have to be signed or known by the initial signer. We propose two techniques: one which transposes the insert-only problem into a delete-only one (which is already solved), and another technique based on zero-knowledge proofs. We also give performance measures and discuss applications.
This paper proves that several interactive proof systems are zero-knowledge against general quantum attacks. This includes the well-known Goldreich–Micali–Wigderson classical zero-knowledge protocols for graph isomorphism and graph 3-coloring (assuming the existence of quantum computationally concealing commitment schemes in the second case). Also included is a quantum interactive proof system for a complete problem for the complexity class of problems having honest verifier quantum statistical zero-knowledge proofs, which therefore establishes that honest verifier and general quantum statistical zero-knowledge are equal: $\mathrm{QSZK}= \mathrm{QSZK}_{\mathrm{HV}}$. Previously no nontrivial interactive proof systems were known to be zero-knowledge against quantum attacks, except in restricted settings such as the honest verifier and common reference string models. This paper therefore establishes for the first time that true zero-knowledge is indeed possible in the presence of quantum information and computation.
This paper describes a new protocol for authentication in ad-hoc networks. The protocol has been designed to meet specialized requirements of ad-hoc networks, such as lack of direct communication between nodes or requirements for revocable anonymity. At the same time, a ad-hoc authentication protocol must be resistant to spoofing, eavesdropping and playback, and man-in-the-middle attacks. The article analyzes existing authentication methods based on the Public Key Infrastructure, and finds that they have several drawbacks in ad-hoc networks. Therefore, a new authentication protocol, basing on established cryptographic primitives (Merkle's puzzles and zero-knowledge proofs) is proposed. The protocol is studied for a model ad-hoc chat application that provides private conversations.
Esoteric protocols, such as electronic cash, electronic voting and selective disclosure protocols, use special message constructors that are not widely used in other types of protocols (for example, in authentication protocols). These message constructors include blind signatures, commitments and zero-knowledge proofs. Furthermore, a standard formalization of the Dolev-Yao intruder [6] does not take into account these message constructors, nor does it consider some types of attacks (such as privacy attacks, brute-force dictionary attacks and known-plaintext attacks) that esoteric as well as other types of protocols are designed to protect against. This paper aims to present an extension of typed MSR [3, 4] in order to formally specify the needed message constructors, as well as the capabilities of a Dolev-Yao intruder designed to attack esoteric protocols.
B. Walter, Marjorie Sadlo, J. Küpfer, V. Niemeier · 8 authors
To the Editor: Itch is a well-known dermatological symptom whose reactions in the brain have been studied very less. In a study with functional magnetic resonance imaging (MRI) response to histamine iontophoresis, McGlone et al (2001) showed that the forebrain regions activated by brief itch (3–4 min) are different from those activated by pain. These findings provide insights into separate motivational and behavioral consequences of itch and pain. In previous studies, Darsow et al (2000) and Hsieh et al (1994) could also identify functional covariates of the itch sensation in the central nervous system by positron emission tomography (PET) analysis. A co-activation of the anterior cingulate cortex, supplementary motor area, premotor area, and inferior parietal lobe was found. Somatosensory areas were significantly activated only in one study (Darsow et al, 2000). All the studies reported above either used stimulation evoking short-lasting itch or recorded brain activation in a short time frame (e.g., 50 s). To our knowledge, there are no studies examining brain activations during the course of longer-lasting skin reactions usually seen after histamine prick. Therefore, we tested brain responses to longer-lasting histamine reaction in healthy participants. Effects of pain due to the prick were controlled by an additional prick condition using saline. Flare, wheal, and itch Following histamine prick, a substantial local reaction was observed. The mean diameter of flares reached 24 mm and showed a maximum about 5 min after prick. Mean wheal diameters increased continuously up to 6 mm at the end of the session. After saline prick, the flare was considerably smaller and a wheal was never detected. Accordingly, ratings of itch intensity and unpleasantness were much higher after histamine than after the saline prick (see Fig 1). Itch intensity/unpleasantness. Time course of itch intensity and unpleasantness (mean curves and standard errors of ratings, possible range: 0–100). Brain activation corresponding to itch was found in eight clusters located mainly in frontal regions. Medial frontal activation took place in the superior frontal gyrus and the gyrus rectus in both hemispheres as well as in a small area of the left anterior cingulate gyrus. Right hemispheric clusters were found in the inferior frontal gyrus and in orbital and dorsolateral parts of the superior frontal gyrus. Further activation was located in the left temporal pole and some parts of the left cerebellum (see Table I and Fig 2). Brain areas of activation. Brain areas of activation (pooled over six subjects) related to itch sensation. Remarks: The numbers correspond to the cluster descriptions in Table I. In comparison, brain reactivity in connection with tonic itch sensations is much more difficult to investigate in functional magnetic resonance imaging (fMRI) analysis than brain reactivity with regard to pain sensations, where short-term reactions can be evaluated. In this study, we demonstrated the brain activation under the histamine-itch condition in eight different areas of the brain in comparison with saline–placebo control. Brain activation was shown mostly in the superior frontal gyrus, in the temporal pole, in the cerebellum, and the inferior frontal gyrus. No activation differing from the placebo control was found in the postcentral gyrus where activation of body sensations was usually found. The gyrus frontalis medius and gyrus frontalis inferior are known to stimulate the motoric activities of the body, in which sensory input is necessary. In the gyrus frontalis inferior, the secondary sensoric cortex is represented and may be activated during itch reactions. In the cingulate areas emotional components of the itch reaction may exist, because the cingulate cortex is known as being highly correlated to emotions. In the temporal pole medial, there is the interpretative cortex that represents experiences and remembrance. Perhaps there the present itch is compared with former itch experiences. But all of these interpretations are still hypothetical with regard to the few studies in this area that looked for activation of the brain. Our results seem to be similar to the finding of McGlone et al (2001), who also showed activation in the forebrain (Brodman's area BA10), an area related to perception (Faw, 2003). Further activations that they found in BA21, BA22, and BA40 could not be confirmed by our results. In the PET analyses of previous studies, Darsow et al (2000), Drzezga et al (2001), Hsieh et al (1994), and Mochizuki et al (2003) identified partly different areas of activation in the anterior cingulated cortex, supplementary motor area, premotor area, and inferior parietal lobe. Hsieh et al (1994) demonstrated the coactivation of the anterior cingulate cortex, supplementary motor area, premotor area, and inferior parietal lobule and underpinned the posterior sector of the anterior cingulate cortex as being related to the sensory/affective aspect of the event. The divergent results may be due to a different method of stimulation with histamine used in this study. We decided to investigate the tonic histamine reaction by prick that produces an itch sensation without producing a substantial pain sensation in a quick and easy way. The PET analyses used in the studies mentioned above have only a very short time frame for revealing activation, whereas fMRI analysis is able to take a longer time period into account. For instance, Darsow et al (2000) described activation for 50 s beginning 2 min after stimulation in the PET analysis. Further studies should evaluate the time course of brain activation during itch. The “pain matrix” (Derbyshire, 2000; Peyron et al, 2000) also comprises very different regions from those identified in our study. Therefore, we assume that brain processes during itch differ substantially from those during pain. But data based on a small sample like ours cannot be take as proof for missing activation. Further studies with larger samples are needed to explore the “itch matrix”. Subjects Six of eight right-handed healthy non-smoking males (mean age: 25.6 y; ranging from 20 to 30 y) were selected for the study. All of them had no history of allergy, no atopic diseases in the family, no current diseases, and no current intake of drugs that could influence the study. The remaining two subjects had to be excluded from further analyses because they reported only a slight itch sensation during the experiment (see below). The study was approved by the ethics committee of the medical faculty of the University Giessen, Germany, and performed according to Declaration of Helsinki principles. Design Subjects participated in the fMRI examinations in separate sessions for each of four experimental conditions: subjects received one prick per session with either histamine or saline to the left forearm. The sessions were conducted in partly permuted order with an interval of at least 1 wk. No information about the substance used in the current session was given to the subjects. Measures and procedure After informed consent for the experimental procedure and for the fMRI examination, the participants learned how to use a visual analog scale (VAS) on a standard PC with a keypad. Then, the subjects were placed into the scanner and instructed on how to use the keypad with their right hand. The VAS were presented on a screen that was placed behind the MR scanner and could be observed by means of a mirror. VAS ratings were performed every minute starting 28 s after the onset of the experiment. The ratings could range from zero to hundred. The extremes of the scale for itch intensity were labeled “no itch” (=0) and “the most intense itch imaginable” (=100). A second VAS was used for the unpleasantness of itch. It was labeled “no itch” (=0) and “the most unpleasant itch imaginable” (=100) (Yosipovitch, 2003). The prick was applied 2 min after the start of the experimental session by using plastic needles (Stallergenes, Anthony-Cedex, France). Wheal and flare diameters were taken every 2 min starting 30 s after the prick. The experimental session lasted 17 min. Analysis of itch ratings Subjects who always rated their itch intensity during the histamine condition always lower than 15 were excluded from analyses. This was the case for two subjects. Due to this loss, data only of six subjects are reported here. Image acquisition and analysis fMRI uses the blood-oxygen-level-dependent (BOLD) response (Logothetis and Wandell, 2004), which is basically an increase of oxygenated blood in areas where neural activation takes place. Fast echo-planar imaging sensitive to BOLD signal was applied to acquire every an image of almost the whole brain 4 s. A fixed-effect general linear model for the fMRI time series at each volume element (voxel) was used in order to compare activation between the two conditions (histamine vs saline prick). The mean time course of itch sensation reported by the six subjects during the histamine sessions served as a regressor for both sessions. The comparison of regression coefficients obtained in histamine and saline sessions gives the activation correlated with itch intensity pooled over subjects. The rating procedure, the prick itself, and head motion parameters were considered as additional covariates for controlling their possibly confounding effects. The significance level was set to α=0.05 after controlling for multiple comparisons due to the analysis of the whole brain volume using the random field theory. This study was supported by the “Institut für Grenzgebiete der Psychologie und Psychohygiene.”
Diese Dissertation befasst sich mit effizienten zero-knowledge Beweisen von Wissen für Homomorphismen. Einerseits\nuntersuchen wir die Effizienzbeschränkungen bestehender Beweise von Wissen für Homomorphismen, andererseits\nbeschreiben wir neue Protokolle, welche diese Beschränkungen zu überwinden vermögen. Die Hauptresultate der Arbeit\nsind die Folgenden:\n- Alle effizienten Beweise von Wissen wurden, vor unserer Arbeit, mittels des Sigma Protokolls erzielt. Wir zeigen auf,\ndass für das Sigma Protokoll inhärente und demnach prinzipiell nicht überwindbare Effizienzbeschränkungen bestehen.\n- Insbesondere waren für die praktisch bedeutsame Klasse von Exponentiations-Homomorphismen in Gruppen unbekannter\nOrdnung (wie z.B., RSA- oder Klassengruppen) bisher keine effizienten zero-knowledge Beweise von Wissen bekannt. Wir\nbeschreiben neue Protokolle, die erstmalig effiziente zero-knowledge Beweise von Wissen für Exponentiations-\nHomomorphismen in Gruppen unbekannter Ordnung liefern.
The recent developments in the mobile technology (mobile phones, middleware) created a need for new methods of protecting the code transmitted through the network. The proposed mechanisms not only secure the compiled program, but also the data, that can be gathered during its "journey". The oldest and the simplest methods are more concentrated on integrity of the code itself and on the detection of unauthorized manipulation. Other, more advanced proposals protect not only the code but also the execution state and the collected data. The paper is divided into two parts. The first one is mostly devoted to different methods of securing the code and protecting its integrity; starting from watermarking and fingerprinting, up to methods designed specially for mobile agent systems: encrypted function, cryptographic traces, time limited black-box security, chained-MAC protocol, publicly-verifiable chained digital signatures The second part presents new concept for providing mobile agents with integrity protection, based on a zero-knowledge proof system.
We consider algebras over a field $k$ of characteristic zero. The article is concerned with the isomorphism of graded vectorspaces \[ H(\gl(A))\iso\wedge (HC(A)[-1]) \] between the Lie algebra homology of matrices and the free graded commutative algebra on the cyclic homology of the $k$-algebra $A$, shifted down one degree. For unital algebras this isomorphism is a classical result obtained by Loday and Quillen and independently by Tsygan. For $H$-unital algebras, it is known to hold too, as is that the proof follows from results of Hanlon's. However, to our knowledge, the proof is not immediate, and has not been published. In this paper we fill this gap in the literature by offering a detailed proof. Moreover we establish the isomorphism in the general setting of ($H$-unital) pro-algebras.
Doctors are expected to keep up to date with the literature, and to change their practice on the basis of what they have read. We believe that the skills needed for evaluating and interpreting scientific papers are often lacking. Even when they are taught, the emphasis is often focused on technical aspects of a paper without consideration of its value, a term we use here to encompass not only the quality of a paper's methods, but also its context and importance. We argue that critical appraisal, the term used to describe the assessment of a paper's methodological niceties [1], should never take place in isolation but must always occur in parallel with assessment of its value, since a paper may be methodologically sound but contribute little to a better understanding of the subject. Here, we discuss various aspects of scientific papers that contribute to or detract from their value, and suggest a stepwise approach for assessing them. The purpose of a scientific publication, of which there are numerous types, is to communicate information. Editorials are summary or personal views, perhaps commenting on a specific paper. Reviews are longer, in-depth analyses of the literature; they are most persuasive when their analysis is objective but their conclusions (as with editorials) are often subjective and personal. Specific forms of supposedly objective reviews are quantitative or systematic reviews, or meta-analyses[2]. Case reports describe one (or more) specific clinical cases, either so unusual as to be of interest, or from which it is hoped some particular lesson can be learned. A letter (correspondence) is a comment on, or criticism of, another's published paper, or seeks answers to a question. A letter may also convey information or data that do not constitute a full study but nonetheless are thought worthy of dissemination. Finally, there are experimental investigations. Broadly, these attempt to answer a question by the use of the ‘scientific method’, which involves the following process [3, 4]. First, the researcher formulates a hypothesis. This hypothesis may represent current ideology (the current theory, or paradigm), or it may be an idea developed de novo (e.g. suggested by preliminary observations). The hypothesis leads to an experimental prediction: if a certain experiment is conducted, then this predicted result should obtain if the hypothesis is correct. A result consistent with the prediction supports the hypothesis, but does not ‘prove’ it (thus scientific proof is very different from mathematical proof). If, on the other hand, the experimental result is not as was predicted, then either the hypothesis is incorrect (so disproved) or the conduct of the experiment was flawed. There are many types of experimental investigations: clinical studies or trials (the terms are often used interchangeably, although the latter is sometimes restricted to investigations of a treatment's efficacy); laboratory investigations; mathematical modelling of data; and some observational studies and audits. We focus here on experimental investigations since these are the papers that advance the knowledge base the most. There are generally two aspects to excellence in an experimental study: first, the study's conduct (of which handling of the data is an inherent part), and second, its presentation. Important aspects of presentation are covered by journals' instructions to authors and by specific publications [5, 6], and we will not discuss these in detail here. First, the study must consider a clear hypothesis that is stated unambiguously, ideally, illustrated by the results that would be expected if the hypothesis were true. The final results and conclusion of the study should relate to this prediction and must either refute or be consistent with the hypothesis. Second, the study must have appropriate ethical approval (or conform to animal research guidelines). We will not consider this issue further, since it has been addressed recently [7]. Third, the technical conduct of the experiment must be sound. Particular attention should be given to the avoidance of surrogate measures, appropriate measurement tools, proper randomisation and blinding, appropriate use of control groups, and appropriate application and interpretation of statistics. We consider each of these below. Surrogate measures or end-points have serious limitations. For example, a study of the control of minute ventilation may not actually involve measurement of this outcome at all, but instead may try to derive conclusions based on the measurement of another, related variable (say, arterial Pco2). The problem is that other factors may influence the related variable (e.g. ventilation is not the only factor influencing Pco2). Furthermore, measures that seem superficially related may not be; for example, although flecainide reduces cardiac arrhythmias, it increases mortality – a much more relevant end-point [8]. Surrogate measures are sometimes used in clinical studies because of the difficulty in measuring the desirable end-point, such as long-term survival. They might also give crude estimates of trends over time for certain variables [9], but they have very little (if any) place in studies that seek to question or overturn fundamental hypotheses in the underlying science. Measuring devices and assessment tools must be valid (measure what they are supposed to measure), accurate (measure the true quantity), and reliable (different users obtaining the same results) – aspects that often escape attention in manuscripts. This is not restricted to technical measurements; for example, assessment of ‘maternal satisfaction’ with the use of a simple visual analogue scale continues widely despite little evidence to support it [10]. When technology is used, coefficients of variation should be given, but rarely are. Further, there ought to be some confidence as to how the technology works. For example, much of the growing literature on the bispectral index (BIS) as a monitor of ‘awareness’ raises concerns. Since it is not known precisely what is being measured by the BIS [11], it can never be known whether an unexpected result has arisen because the BIS is invalid or inaccurate, or because the hypothesis being tested is incorrect [12]. Randomisation and blinding are intended to minimise the influence of bias. The hope with randomisation is that all ‘confounding factors’ (both known and unknown) that might influence the outcome will be distributed equally amongst the groups. If any differences are found they can therefore be attributed to the sole factor – the treatment under study – that has not been ‘shared out’ in this way. However, even with proper randomisation, groups may be unequal: chance alone might result in one group's subjects being older, heavier, younger or just luckier than those in the other group. Even when groups appear equal, small inequalities might combine to influence the results. For example, in a study by Greif et al. [13] into the possible anti-infective effect of peri-operative oxygen therapy, patients randomly allocated to receive extra oxygen were by chance more likely to be fitter and less likely to be smokers, to have inflammatory bowel disease, and to undergo rectal surgery than those in the ‘no oxygen’ group. Could these factors have combined to contribute to the dramatic reduction in infection seen in the ‘oxygen’ group, such that a subsequent study obtained completely the opposite results [14]? In addition, the human urge to guess or manipulate treatment allocations, or otherwise interfere with proper randomisation in studies, is well reported [15]. Blinding is present when the person treating the patient, or making the assessments, does not know which patients receive which treatment. Some studies fail to take even the simplest steps to ensure blinding, while others go to extraordinary lengths (for an example of the latter, see Smith and Thwaites's [16] commendable study comparing intravenous with inhalational anaesthesia). Occasionally, blinding is impossible (e.g. when comparing two different laryngoscope blades or bougies [17]), but the results of a blinded study are always more persuasive. Indeed, studies with insufficient blinding tend to report greater treatment effects than those with proper blinding procedures [15]. Control groups may be inappropriate because of poor randomisation or blinding. Even if these are sound, though, there may be other reasons why treatment effects may be masked or exaggerated by problems with control groups: lack of consideration of other possible ‘confounding factors’; use of historical, rather than contemporaneous, controls; comparison of a treatment against placebo instead of standard practice, or against an inappropriate treatment; or (at worst) lack of a control group at all. Much of the above might give the impression that the testing of hypotheses by close attention to the study's conduct will always give a clear-cut result. Unfortunately, this is not the case, because we can never achieve certainty; the best we can do is use statistical analysis to indicate the degree of uncertainty [18]. A full discussion of statistical methods is dealt with elsewhere [19], and here we consider only two related areas that commonly cause difficulties: significance and power. Significance. If, in a study, one drug appears more effective than another, the traditional approach is to ask the question: ‘What is the likelihood (or probability) that this result is a chance finding, and that these two drugs are in fact equivalent?’ This approach (testing the equivalence, as opposed to testing the difference) is known as testing the null hypothesis. It is important to stress that this null hypothesis assessed by the statistical test may not always be exactly the same as the underlying scientific hypothesis being examined by the study as a whole: the result of the former will help interpret the latter. Many statistical tests ultimately generate a ‘p-value’: the lower the p-value, the less likely it is that the null hypothesis is correct. A p-value of 0.03 indicates that if the two drugs are indeed equivalent, chance alone would be expected to yield the observed results three out of every 100 times one conducted the study. Conventionally, a p-value of < 0.05 is taken to represent ‘statistical significance’, although this value can and should be adjusted in certain circumstances, for example if multiple comparisons are made [20, 21]. Confidence intervals can be used as an alternative to testing the null hypothesis [22, 23]; nonetheless, the conclusions reached by using confidence intervals are invariably the same. The real problem lies in how p-values are interpreted rather than how they are calculated [24]. An entirely different approach is to interpret a study's results mathematically in the context of prior knowledge (Bayesian statistics) [25, 26]. Regardless of the method of calculating or presenting statistical significance, the smaller the p-value, or the further away from zero the difference in confidence intervals, the less likely the result is to be a ‘chance’ finding and therefore the more likely it is that the difference between the two groups is indeed ‘genuine’. But such a chance finding is still possible, albeit unlikely; as Counsell et al. [27] point out, chance ‘…doesn’t get the credit it deserves'. Furthermore, a low p-value does not exclude poor methodology in the conduct of the study. Power. If the p-value in a drug study is, say, 0.07, does this mean there is genuinely no difference between the two drugs? Or does it mean that there might be a true difference, but that the study has simply failed to show it? It is specifically to help answer such questions that a power analysis is useful. The power analysis estimates how likely it is that a negative result can be ‘believed’. One emerging problem is that some researchers (or their critics) are placing far too much emphasis upon power analysis [28]. One example demonstrates the type of misplaced faith in power analysis: ‘…at least 400 patients would be required to prove there is no statistically significant difference between the groups…’[29] (our emphasis). Such statements reveal a poor understanding of the scientific method and of the concept of scientific proof. One reason for our concern is that the concept of power analysis itself has very serious limitations. Power analyses are only crude estimates of a sample size (indeed, the word ‘crude’ is emphasised by statisticians [30]). For example, two main elements that contribute to power for normally distributed continuous data are the difference between the means that is deemed important and the expected standard deviation (SD) of the measure of interest. Both of these are subject to serious shortcomings. The choice of what constitutes an ‘important difference’ is almost entirely subjective, and small but arbitrary adjustments to its value can have a great impact upon a study's calculated power. Where no previous data exist, the expected SD is usually taken from a pilot study, often without a control group, and by definition always smaller and less robust than the planned substantive study. In reality, the power analysis itself is probably best expressed in terms of a confidence interval: for example, ‘Power analysis indicated that we would require 20–60 subjects to be 70–90% confident of detecting a difference between the means of 10–50 s’– although this is rarely done. The crudeness of the power analysis as a tool is reflected in the different sample sizes yielded by different methods. If we assume that for a hypothetical study, the important difference is 1.0 arbitrary units, with a standard deviation of 0.8 arbitrary units, then various calculations give a sample size per group (with 80% power at p < 0.05) of 10 [30], 11 [31], 13 [32] and 18 [33]. So at best, power analysis only gives an approximate estimate of sample size. Indeed, Bacchetti [34] has suggested that a study's power should only be criticised if the study has no other shortcomings; in other words, all other features of a study (especially relating to its conduct) are far more important than its power analysis. In practice, the actual sample sizes of studies are related to the type of outcome, the variability of the result and the statistical test used. We observe that in published studies, sample sizes tend to fall into three groups, though with considerable overlap in which the outcome is and or there is little variability with factors (e.g. laboratory or studies in which experimental can be with use smaller sample usually increases patients are since are to studies comparing have sample in which the outcome is variability is great factors are much sample sizes It is how often studies and their sample sizes fall into these groups. It is to whether this is a of proper power analysis the of each study, whether tend to use sample sizes because of the in their particular of or whether they even the power calculations to yield sample sizes that the study to be a There are ethical reasons for power calculations as well as scientific and we do not suggest that should but given the crudeness of these calculations we help but whether the crudeness of is any It can be seen from the above that studies, despite their not to subjects in advance – as they do on data – are than have to on surrogate measures, using tools that be with little of blinding and of the groups and their The one of studies is the with which very can be So much for a paper's We to a different question: what one paper more than another, proper and attention to their some the answer to this question will always be subjective and upon the interest, and However, we suggest that there are some elements that contribute to a paper's We these as being related to the the type of question addressed and the answer the of the evidence certain aspects of a paper. The of the type of question to its This will on the (e.g. of the person assessing the paper, the significance of the problem being and whether the and appropriate question is being For clinical studies, the of a paper can on the of the change in practice likely to from the the with which that change might and the of such a For example, the that the of and their more and than alternative drugs The problem it addressed of is relevant to a of and is and serious to it a very significant Furthermore, the question was more effective than was stated and appropriate for current knowledge at the The change in clinical practice by the study was and to was predicted to result in a reduction in and mortality Indeed, practice and as a result A particular of the is that it a clear and is more effective than its and we should use it to of The of for the of still in an of great clinical and significance, as many questions as it reduces the of but whether we should give it to all is less certain This example that sometimes the of a paper's conclusion can its as well as the of the question in the in which the answer may a paper's value to the of information For example, a study of the effects of on in the and of the reduction in and other but not the or In whether the reduction in might be or for a particular patient, knowledge of the likely of the best and might be more relevant than how the of patients might be the value of the study is by this the value of the published paper is as a result. For studies in it is perhaps the effect on which is likely to be rather than any For example, in the the of no but certain better than more traditional An example from the of papers that we is the that is a is the finding that is fundamental to this to in a all in which the of the is The in these but there are many less well known For the of a that specific and that is to by the to consider the that this is a if not by which may be at the It is possible indeed to clinical and scientific of The of in are to from to a clinical problem to the a approach to its results would be to consider whether there is a fundamental reason why better than other and that this reason will help more as a However, we must that in related finding the between and clinical is not The of to is not always to and can often be by the to control all the variables in clinical of the type of question which can equally to clinical and is its and – if the study's results can be into an are to the more than and this can sometimes to the of proper scientific by a A example is the of study of the between and in the impact factor – see and then the subsequent of this paper In the scientific a very of the of studies appears to have in upon the type of question This to have been by the with for and we discuss these further below. The of the evidence in a paper first, on those methodological aspects second, on the greater to certain types of study over a by and When assessing the of the would do well to ask (as indeed the should have there possible for these results other than the conclusions methodology and attention to the above aspects may or many of these alternative but the more that and the less the that should be to a of results. This approach may seem an negative but we to of it as a of and for a scale of the of evidence in studies is in The emphasis on as a tool has been much criticised Some have that is, in a of rather than that has no place in scientific studies to test hypotheses The to clinical and not to scientific argue that fundamental hypotheses in can only be addressed with the scientific as by a conducted experiment to test the prediction from the hypothesis, and not by simply the results of different of It is possible that is more for those studies of a drug or or for rather than problem with is that it reports and to the of the of evidence In many areas of in the more such as reports can have a very persuasive effect on an clinical practice, since they are based on clinical and not on trials in which may be masked by into and summary statistics. If a a drug and for example, then that drug may cause the results of a clinical Case reports are for very for very or when they describe unexpected clinical (or We the above term to those aspects of a paper not relating to its scientific or but which nonetheless seem to have an and influence on the in which papers are by the scientific or clinical The the was out is one of these For example, from the of or is likely to have greater impact than of say, a The can be criticised for this the obtain better and can more which in is as more since it from the and so on A related issue is the for authors to their to the quality and they to its importance. A quality is by a the impact factor index of how often papers published are by other the impact factors have some a paper published say, a will have very of its scientific quality and so is to be widely though, impact factors are a poor measure of a and are to by However, some authors and perhaps also the to a paper's by the in which it is The of the authors (or at least one of may also have an A study a current fundamental hypothesis is more likely to be and if a is an It is perhaps that an is to time on Finally, the of a study can influence its importance. A study's support from a (e.g. or gives the impression that the or at least its preliminary has some and that in a it has been discuss this further The of areas for research by the and superficially but may the influence of certain since it is that studies the current areas are more However, aspects can of that the impact of a paper (e.g. when has been obtained from to support a paper relating to research However, such may be and we have how an might critical a have developed by which they or a process of to their which research to the the study is conducted or the that the published from the study will have a value to this the published by which it research It is clear that particular emphasis is given to that have a impact on practice or scientific and to those that are important in terms of or knowledge of The for of each to support research and research and the is the method used to these to the the most The used by although not made seem to place emphasis on the of to by of as those to the in and to papers in impact factor In the they receive to using our impression of the types of paper which seem to more in this are to much criticism and whether they critical is to However, they de the means by which research is If a as on research which does not a value in these then these will ensure (as they are to that the as so will research and research and then it may impossible for that to conduct any research at all. Many authors have how is in such a So while critical of papers by an (or by a might to one by may to a different The for a in this is to consider the to which it to (or of from We have various aspects of a paper that can contribute to its We here by an approach to a paper, based on the a hypothetical of with the the most papers and the the The is to go each paper and at the of the be to place it in the appropriate of the above factors – aspects of the study's conduct of other aspects of its methodology not covered the of the question and the answers the of the evidence and any persuasive factors – should be at intervals when a paper, and each has the to the paper up or to the impression The steps are in this process the paper can be or many times up in its final in two First, every paper will have some value, even if it up in the any a paper should be for what is all a considerable in the current Second, different may place the same paper into different final – but this is a and appropriate of value in any of the paper with or the should be reasons for the paper to a particular and for being in various (or by all aspects of the paper. This it to to others how the process of and is a of discussion and which is a process in We also by our to some One of our is to the value of all any given paper, the should can we further on the approach used to answer the question The specific answer to this will in on the of the paper we have indicated above some of these might However, in to these by a better study or the researcher will the serious problems the as a those related to discussion above two important questions to First, if is so critical to studies to be conducted, then we should not to what we alone value, but also ‘What do the Second, any given which as a there are always a of possible questions we might It is here to specific questions or hypotheses this will the value of our It is possible that for the of to our others place value on hypotheses different from those the has We hope that our discussion above might generate a which answer these two is an of this in in all aspects of the conduct and of is the of the of with the report on the for and Both have of and clinical and have papers that they have been more The above are the and do not of the of the of of and or the of
A central concern of this research has been to understand more about how and why organisations change. My initial research question posed was: What is 'strategy', how does it emerge in health care organisations and how can I influence its development? This is explored within the context of my field of practice as a Director of Nursing in a National Health Service (NHS) Trust. I have approached this enquiry through using a methodology known as emergent exploration of experience (Stacey et al., 2003). This methodology is informed by insights from Complexity Science and the theories of complex responsive processes of relating. What emerged through the enquiry were a number of key areas of concern related to national healthcare strategy and the management of risk within my NHS trust. The findings from this research radically challenge the way we are practising together in my organisation in moving from the position of locating accountability for mistakes with either the individual or the system. Instead it is suggested that, as part of our ongoing process of interaction, we co-create what others are describing as a 'system' through our participation with each other. Accepting the notion of co-creation requires us to examine very carefully the influence of our own participation in the dangerous situations that arise in our everyday work, and to acknowledge our own accountability for what emerges. I am proposing that this makes a new contribution to knowledge in this field for two reasons. First, because it explores for what I believe to be the first time the validity of the theory of complex responsive processes in the discourse of risk management in health care. I am proposing that this theory has a legitimate contribution to make in this field of practice, that is worthy of further enquiry and research. Second, in making this shift to a perspective that understands accountability for error as something that we co-create in groups, my thesis poses a radical challenge to many of the activities that are traditionally undertaken when mistakes occur in organisations. Specifically, I have questioned the usefulness of approaches that seek remedies through focusing on individuals outside the context of the group and those that focus on re-engineering what other authors refer to as the 'whole system'. I offer an alternative through describing examples in my narrative of a different approach grounded in the research methodology of emergent exploration of experience. This focuses on the micro-interactions between participants in groups as a way of understanding the transformation of practice .I am arguing that such transformation may not always be an improvement, because we cannot always accurately predict the outcomes of our actions in advance. This perspective therefore also challenges the assumption made by some authors in this field, who believe it is possible to 'human-proof' systems and thus guarantee ‘zero defects'. In seeking an answer to my research question I have therefore moved from understanding strategy as a vision for the future that can be planned and implemented by a few powerful individuals whom others follow to a different understanding. I now see strategy as an emergent phenomenon arising from micro-interactions between people in the present – hence we co-construct our future as the actions we take in the present. From this perspective I have argued we all have the potential to influence what is emerging through our actions, for which we are constantly held to account, through both our inner dialogue with ourselves and our conversations with each other.
Practical knowledge on the design and application of multi-objective evolutionary algorithms (MOEAs) is available but well-founded theoretical analyses of the runtime are rare. Laumanns, Thiele, Zitzler, Welzel and Deb (2002) have started such an analysis for two simple mutation-based algorithms including SEMO. These algorithms search locally in the neighborhood of their current population by selecting an individual and flipping one randomly chosen bit. Due to its local search operator, SEMO cannot escape from local optima, and, therefore, has no finite expected runtime in general. In this talk, we investigate the runtime of a variant of SEMO whose mutation operator flips each bit independently. It is proven that its expected runtime is O(n^n) for all objective functions f: {0,1}^n -> R^m, and that there are bicriteria problems among the hardest problem for this algorithm. Moreover, for each d between 2 and n, a bicriteria problem with expected runtime Theta(n^d) is presented. This shows that bicriteria problems cover the full range of potential runtimes of this variant of SEMO. For the problem LOTZ (Leading-Ones-Trailing Zeroes), the runtime does not increase substantially if we use the global search operator. Finally, we consider the problem MOCO (Multi-Objective-Counting-Ones). We show that the conjectured bound O((n^2)log n) on the expected runtime is wrong for both variants of SEMO. In fact, MOCO is almost a worst case example for SEMO if we consider the expected runtime; however, the runtime is O((n^2)log n) with high probability. Some ideas from the proof will be presented.
Abstract. In undeniable signature schemes, zero-knowledgeness and non-transferability have been identified so far. In this paper, by separating these two notions, we show the first 3-move confirmation and disavowal protocols for Chaum’s undeniable signature scheme which is secure against active and concurrent attacks. Our main observation is that while the signer has one public key and one secret key, there exist two witnesses in the confirmation and disavowal proofs of Chaum’s scheme.
Abstract. A shuffle consists of a permutation and re-encryption of a set of input ciphertexts. One application of shuffles is to build mix-nets. We suggest an honest verifier zero-knowledge argument for the correctness of a shuffle of homomorphic encryptions. Our scheme is more efficient than previous schemes both in terms of communication and computation. The honest verifier zero-knowledge argument has a size that is independent of the actual cryptosystem being used and will typically be smaller than the size of the shuffle itself. Moreover, our scheme is well suited for the use of multi-exponentiation and batch-verification techniques. Additionally, we suggest a more efficient honest verifier zero-knowledge argument for a commitment containing a permutation of a set of publicly known messages. We also suggest an honest verifier zero-knowledge argument for the correctness of a combined shuffle-and-decrypt operation that can be used in connection with decrypting mix-nets based on ElGamal encryption. All our honest verifier zero-knowledge arguments can be turned into honest verifier zero-knowledge proofs. We use homomorphic commitments as an essential part of our schemes. When the commitment scheme is statistically hiding we obtain statistical honest verifier zero-knowledge arguments; when the commitment scheme is statistically binding we obtain computational honest verifier zero-knowledge proofs. Key words. Shuffle, Honest verifier zero-knowledge argument, Homomorphic encryption, Mix-net. 1