A set of ethical principles for design science research in information systems Over the past decade design science research (DSR) has re-emerged as an important research paradigm in information systems. However, the current recommended approaches to conducting design science research do not consider ethics. Hence the purpose of this paper is to begin a debate about the need for ethical principles in DSR in IS. In order to start this debate we suggest a set of ethical principles for DSR in IS. While the interpretation and application of the principles might not always be straightforward, our argument is that all design science researchers in IS should give some consideration to ethics. In recent years design science research (DSR) [1] [2] [3] Venable and Baskerville [4] define Design Science Research as "Research that invents a new purposeful artefact to address a generalised type of problem and evaluates its utility for solving problems of that type" (p. 142). Unlike the social science or behavioural science paradigms that had come to dominate IS research -where the main objective of the researcher is to understand the world -DSR builds on the engineering tradition of research in which the whole idea is to invent new technologies or artefacts that can be used as ways to change (and hopefully improve) the world. Design science researchers create new artefacts (e.g. new software, processes, and systems) that are intended to improve the effectiveness or efficiency of an organisation, [1] to improve people's health, education or quality of life [5, 6] , and to improve community interaction and well-being [7] . Hence the explicit purpose of DSR is to create new artefacts and knowledge about them whereby people can change and improve the world in which we live.. Over the past decade a rich literature in design science research in IS has developed. Many processes and methods for conducting DSR have been proposed, from the simple "buildevaluate" cycle [1, 2] to more elaborate linear processes (with feedback loops) [3, 8] , flexible processes [9] , methods supporting participation and researcher-user interaction [7, 10, 11] , and methods combining DSR with Action Research [10, 12] . Several works have developed and debated the content and form of design theories, as formalisations of the knowledge created in DSR [13] [14] [15] [16] [17] [18] [19] . The most seminal work though, which can be credited with reinvigorating DSR in IS, is that by Hevner et al [1] . This article suggests guidelines for conducting DSR and has become one of the most cited papers in the IS field.. However, we believe there is one notable omission in all of the current recommended approaches to conducting design science research. The guidelines and methods proposed so far focus on the viability, efficiency, and effectiveness of the artefact, but they do not include any consideration of ethics. In other words, the current guidelines simply assume that efficiency and effectiveness are always "good" and that the design science researcher knows what is best for improving business or society. But what if people disagree about what is "good"? What if the artefact improves the effectiveness and efficiency of spying on all citizens? We suggest that the lack of any ethical guidelines for design science researchers in information systems could lead to problems in the future, and could potentially harm the reputation of the IS field as a whole. We believe that the lack of any ethical guidelines is a significant omission in the contemporary theory and practice of design science research in information systems.. Hence this paper is intended to begin a dialog and debate about the need for ethical principles in DSR in information systems. To begin this debate we suggest a set of ethical principles for DSR, although we wish to emphasize the tentative nature of our principles at this stage. We have identified four potential sources for the development of a set of ethical principles for design science research in IS. We acknowledge that there are many other sources that we could have used, and we are certainly not suggesting that these four are necessarily the best or only ones that could be used. However, we believe that the four sources we have identified are relevant to our purpose (as explained earlier), and represent at least a starting point in the debate about ethical principles for DSR in information systems. We also acknowledge that all four sources have their weaknesses. For example, Principle 1 of the ACM/IEEE-CS Software Engineering Code of Ethics and Practice says that the public interest should come first, but determining what is in the public interest is not always obvious. In fact, there may be genuine disagreements and debate about the public interest. Venable's application of critical systems heuristics is also not straightforward, since following one point in the framework may compromise another and put people at risk. The next section attempts to integrate these four sources into a coherent set of ethical principles for DSR. The purpose of this paper is to initiate a dialog and debate about the need for ethical principles in design science research in information systems. To this end we have suggested a set of ethical principles for DSR in IS. We would like to emphasize once again the tentative nature of our principles: they are simply a suggested set of ethical principles, the intention being to start a debate on this important subject.. We freely acknowledge that there are many other ethical frameworks that we could have used, such as those based on Aristotle's ethics, Kant's categorical imperative, or postmodern ethical philosophers such as Mackie or Lyotard. However our hope is that IS researchers will build upon, refine and modify the ones we have provided as needed. Our suggested set of principles are a stake in the ground for design science research. We believe it is imperative that all design science researchers should consider the ethical dimensions of their work and the ones we have proposed are directly relevant to the conduct of research involving the design of IT by, with, and for people.. Our suggested principles are not intended to be overly prescriptive. They allow a degree of freedom on the part of the researcher to decide which principles might be more applicable in a given situation than others. We also caution that there are ethical dilemmas. Sometimes it is not easy to decide how a particular principle should be interpreted, or if two principles conflict, which principle should have priority. However, we believe it is better for design science researchers to at least thoughtfully consider these ethical dilemmas, than to not consider ethics at all.. One contribution of our paper has been to show that the ethical principles that apply to social science and behavioural research (the paradigm that has dominated IS research until recently) are insufficient for DSR; they are insufficient because they ignore the potential of an artefact to affect the public at a later date. Following the lead of the ACM and other computing and engineering societies, we believe that the public interest should take priority over other ethical considerations. A design science researcher in IS should consider the public interest over and above his or her responsibilities to the user or organization involved in the research project. This suggests to us that a body such as the Association for Information Systems might want to reconsider its current ethical guidelines.

O O O B I O B I I O O O O O O O B I I O O O O O O O O O O O O O O O O O O B I I O O O B O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O B I I O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O B I O B I I O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Finite-valued Logics for Information Processing We examine the issue of collecting and processing information from various sources, which involves handling incomplete and inconsistent information. Inspired by the framework first proposed by Belnap, we consider structures consisting of information sources which provide information about the values of formulas of classical propositional logic, and a processor which collects that information and extends it by deriving conclusions following from it according to the truth tables of classical logic, applied forward and backward. Our model extends Belnap's in allowing the sources to provide information also about complex formulas. As that framework cannot be captured using finite ordinary logical matrices, if we want to represent each of the relevant logics with a single matrix, we employ Nmatrices for that purpose. In opposition to the approach proposed in our earlier work, we assume that the information sources are reasonable, i.e. that they provide information consistent with certain coherence rules.We provide sound and complete sequent calculi admitting strong cut elimination for the logic of a single information source, and (several variants of) the logic generated by the source and processor structures described above. In doing this, we also provide new characterizations for some known logics. We prove that, in opposition to the variant with unconstrained information sources considered earlier, the latter logic cannot be generated by structures with any bounded number of sources. The goal of this paper is to present some novel applications of logics with finite-valued semantics (especially three-valued and four-valued ones) to information processing, and their relationships with some well-known previous approaches in that area. Our practical motivations stem from the necessity to deal on a daily basis with vast amounts of information provided by a multitude of various sources. That information is often incomplete or inconsistent -but we nevertheless need to draw reasonable conclusions from it, and use them a basis for our decisions and actions.. The first researcher to propose a logical framework for dealing with the above issue was Belnap. His famous model, presented in [11, 12] , consisted of information sources which provided information about the values of atomic formulas of some logical language, and a processor which collected and processed information from the sources. Belnap's model was later extended by Carnielli and Lima-Marques [14] , but none of the above proposals went beyond the simple case of sources providing information solely about atomic formulas.. As this is insufficient for dealing with many situations commonly encountered in various information environments, in this paper we consider a more general approach, where the sources may also provide information about complex formulae. Moreover, we assume that the sources are reasonable in the sense of providing coherent and consistent information.. The rest of the paper is organized as follows. In Section 2, we introduce logical preliminaries, and present the basic finite-valued matrices used for reasoning about information processing. In Section 3, we define the information processing framework discussed in the paper. We start with presenting Belnap's basic information processing model, and proving its correspondence to Dunn-Belnap's four-valued matrix, and in case of complete information -to Asenjo's-Priest's three-valued matrix. Next we define general information processing structures for an arbitrary language L, and the logics (consequence relations) introduced by classes of such structures. Section 4 is devoted to information processing structures for the language L C of propositional classical logic. We begin with defining the notions of an information source and the standard information processor for L C , and giving an effective way to compute the final valuation generated by such a processor. Then we define a standard existential information processing (EIP) structure for L C . After recalling the notion of non-deterministic matrices (Nmatrices), we prove that the class of information sources is identical with the class of legal valuations in a certain three-valued Nmatrix, and the class of all processor valuations generated by EIP structures -with the class of legal valuations in a certain four-valued Nmatrix (and in case of structures providing complete information -in another three-valued Nmatrix). We also show that none of the corresponding consequence relations can be generated by a single ordinary finite-valued matrix. Finally, we prove that there are EIP processor valuations which cannot be generated by a finite number of source valuations, and that the logics generated by classes of all EIP structures with at most n sources are different for different values of n, as well as different from the logic generated by the class of all EIP structures. In Section 5, we present sequent proof systems for all the six considered logics, and prove their strong soundness, completeness and cut-elimination. Section 6 presents an outline of future work. A natural next step in our research will be to extend the language of EIP structures with suitably interpreted quantifiers to obtain a first-order logic of information processing structures. Another direction is to consider other strategies for collecting information from sources, or to use more than four truth values to characterize the information they provide about formulas.. Further, the problems considered in our work bear an obvious relationship to the works on on social choice, e.g. [14, 15] , where a group of individuals aggregate their individual judgments on some interconnected propositions into the corresponding collective judgment. Hence another direction of future work would be to try to apply our approach to the problems of social choice.

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A Pay-and-Stay model for tackling intruders in hybrid wireless mesh networks Intrusion handling in wireless mesh networks (WMNs) is a relatively less addressed topic. The difficulty may lie in the fact that there are other wireless networks for which some intrusion detection or prevention schemes are proposed that could also be applied in some way in a WMN setting. As those schemes are contributing, researchers may not find it necessary to specifically focus on this field. Another critical reason may be the difficulty in developing an effective scheme for WMNs. In fact, the structural differences among various wireless ad hoc networking technologies make it imperative to devise the mechanisms in subtle but critically different ways. For WMNs, there is a proper network backbone that is called mesh backbone (which is not present in many other wireless network counterparts), which supports the fringe part or the mesh clients. Hence, it is often possible to install the intrusion handling mechanisms or agents in the stable part and allowing some flexibility in the client or fringe parts. Nonetheless, instead of thinking in this pattern, we take a different approach of tackling intrusion by allowing an intruder to stay in the network as long as it proves to be worthy of staying in the network by supporting the network's regular activities. The idea is that by not always directly purging rogue entities, one could exploit the intruder's resources, thereby benefiting the network. We call our approach an intrusion-tackling mechanism and term it a Pay-and-Stay model. Alongside presenting the details and analysis of our model, in this paper, we also present the basics of various forms of intrusion handling in such types of networks. Using our evaluation results, we found that the model could be very effective in handling intruders and defending the network against a broad range of security attacks. Wireless mesh networks (WMNs), using IEEE 802.11s or IEEE 802.16j allow the multi-hop Internet access to extend the network service coverage without connecting each access point to the wired network. 1, 2 This technology could significantly reduce the investment and maintenance cost of wireless connectivity to cities, municipalities, and other end-users, because of which the WMN has become a very popular topic of research in the recent years. However, popularity cannot conceal the inherent weakness that it has as a wireless network. Like any other wireless network, the secure authentication with access control and various security issues still remain in this field as a paramount issue to ensure proper service to the legitimate users, while preventing a variety of attacks. Most of the security threats are posed by the illegitimate entities that enter or intrude within the network perimeter, which could be commonly termed as intruders. Sometimes a legitimate node could also be compromised in some way so that an attackerintended task for 'security breach' could be performed. We, in this paper, term any such kind of rogue node or entity as an intruder. So, the main objective of this work is to identify any kind of intrusion in a WMN and handle it in a sophisticated manner so that a wide range of security attacks can be deterred, as well as the network being benefited. As we go along through the paper, we will explain the concepts and motivations behind our approach.

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Analysis of benefits, opportunities, costs, and risks (BOCR) with the AHP-ANP: A critical validation This paper shows that the usual multiplicative synthesis of alternative priorities for benefits, opportunities, costs and risks, obtained from separate Analytic Hierarchy or Network models, can be ambiguous. The ratio of benefit and opportunity priorities to cost and risk priorities can be misleading when assessing the profitability of a project. The same holds for their additive synthesis. Both types of synthesis have been advocated in AHP/ANP literature. A quotient of these priorities with weights as coefficients, not powers, will however produce sound results, provided that the four separate models are properly related to each other by weights that make the priorities on the four factors commensurate and are obtained from magnitude comparisons. Similarly, additive synthesis with properly weighted factor priorities based on relative magnitudes will produce sound results, although use of reciprocal values of costs and risks, as often advocated in the literature, is not recommended; negative costs and risks priorities should be used instead. A decision on whether or not to undertake a project usually requires investigating the positives (benefits) and negatives (costs) of that project and an attempt to express those in monetary terms such as dollars. If that project has a benefit/cost ratio >1, its benefits outweigh its costs. If there are several projects to choose among, those projects will usually be ordered according to their respective benefit/cost ratios. The ones with a ratio >1 are the attractive ones exceeding the break-even point, and the one with the highest ratio among these gives the highest return on money spent and would therefore very likely be the one to be chosen.. The problem is that often benefits and costs are difficult to express in monetary terms, especially when some of the benefits or costs are intangible, such as "improved accuracy" or "learning efforts". The Analytic Hierarchy Process (AHP) developed by Saaty [1] has been advocated as an approach that not only can deal with both tangibles and intangibles but also helps organize all aspects involved in a hierarchic structure where the benefit or cost aspects act as criteria and the projects as alternatives. Usually, we have separate hierarchies: one costs hierarchy and one benefits hierarchy. One has to pairwise compare the importance of cost criteria in the cost hierarchy, and the same with respect to the benefit criteria in the separate benefits hierarchy. These processes produce relative criteria weights expressed on a derived ratio scale, usually normalized to the unity sum for each family of criteria in each hierarchy. The alternative projects are pairwise compared with respect to each criterion on the lowest level of each hierarchy; their derived priorities are expressed on a ratio scale as well, again usually normalized to the unity sum per criterion. Synthesis of the alternative priorities and the criteria weights using a weighted sum produces composite alternative priorities for each hierarchy. For each alternative, its composite benefit priority is then divided by its composite cost priority. The resulting ratio value serves as a means to rank the alternatives and choose the best one, i.e. the alternative with the highest benefit/cost-priority ratio. Examples of benefit/cost analysis using the AHP were published in Saaty [1, 2] .. Benefit/cost analysis with the AHP has been criticized though. The main criticism is that different hierarchies produce priorities on different derived ratio scales which are usually not commensurate. The quotient of two ratio scales is again a ratio scale but has lost its clear relationship with the individual scales. The result may therefore appear meaningful as a measure of profitability, whereas it is in fact not: benefit/cost-priority ratios may be larger than unity when in fact the monetary costs exceed the monetary benefits. This is demonstrated in Wedley et al. [3] .. Wedley et al.. [4] reviewed previous literature which proposed procedures for proper benefit/cost analysis with the AHP, including suggestions by Saaty [2, page 151] to produce more meaningful ratios. Wedley et al.. [3] suggested a formal magnitude adjustment procedure that converts the benefit and cost hierarchies to a common unit thus assuring that resulting benefit/cost ratios do have the desirable property of correctly indicating the break-even point. The questioning procedures they proposed are however cognitively difficult. Wedley et al. [4] proposed using linking pin methods, thereby potentially easing the questions for relating benefits to costs.. In the AHP literature thus far, only risks (R) have been added to the B/C ratio, see for example Saaty [2, [164] [165] [166] . For each alternative a B/(C * R) ratio is computed based on priorities that are obtained from three different hierarchies: a benefits, a costs, and a risks hierarchy. More recent publications by Saaty [5] and Saaty and Ozdemir [6] showed that a fourth factor, opportunities (O), can be added to the analysis. This allows a full BOCR analysis using a (B * O)/(C * R) ratio where positives not only include benefits but opportunities as well, and negatives not only costs but also risks. A full BOCR analysis is in some ways similar to a SWOT analysis, where not only the strong points (S) of a firm but also its (external) opportunities (O) are taken into account such as good chances of entering a new market and other favourable situations. Opportunities in BOCR analysis usually catch expectations about positive spin-off, future profits and revenue of future positive developments, whereas benefits represent current revenue or those profits from positive developments one is relatively certain of. Likewise, a firm's weak (W) points may not tell the whole story of negative aspects in SWOT analysis; external threats (T) concerning competition or unfavourable developments in society must be dealt with as well. Risks in BOCR analysis are supposed to catch the expected consequences of future negative developments, whereas costs represent (current) losses and efforts and consequences of negative developments one is relatively certain of. BOCR analysis enables therefore a potentially richer analysis than a mere BC analysis, although many of the aspects that define the factors and their relationships are usually difficult to specify and quantify.. Recently, the Analytic Network Process with supporting software was developed by Saaty [5] , enabling one to model systems with feedback and dependence. Especially in the context of the ANP, many applications of BOCR analysis are offered where a network model with one or more networks for each of the four BOCR factors is set up instead of a hierarchy. This allows for modelling interrelationships between the elements defining each of the four overall factors.. Not only B/C analysis but also B/(C * R) analysis has been criticized, for example by Millet and Wedley [7] . These authors argue that the product of costs and risks is not meaningful or justified, with the added argument that differences in relative importance are not accounted for. Similar arguments may hold for BOCR analysis as well. Furthermore, it has been argued (Wedley [8] ) that opportunity and risk priorities could be regarded as probabilities. Higher opportunity and risk priorities would then represent greater opportunity or risk likelihoods, and their products with benefit and cost priorities, respectively, would produce expected benefit and expected cost values. This paper does not enter into this discussion, although it does, for other reasons that will become clear later on, criticise the quotient of products as proposed by Saaty [5] . This paper will not question a BOCR analysis per se, nor will it address the way in which composite alternative priorities on each of the four merit factors (B, O, C, R) are computed, be it using AHP-based or ANP-based models. It is rather the computational method for getting meaningful synthesized results that is the paper's subject. It therefore

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


GLP: A cryptographic approach for group location privacy Recently, location privacy during the use of location-based services (LBSs) has raised considerable concerns. There is a wide literature on location privacy from the individual point of view; however, there exist only a few works to support location privacy for a group of users. In this paper, we consider location privacy issues for a group of users who may ask an LBS for a meeting place that minimizes their aggregate distance. The proposed solution, which we call the Group Location Privacy (GLP) protocol, is based on the Anonymous Veto network (AV-net) and homomorphic encryption. It preserves the location privacy of all users even in the case of collusion. Our solution also tries to minimize the LBS overhead for nearest neighbor (NN) queries and communication, i.e., to decrease the number of NN queries sent to an LBS and the number of points of interest (POIs) it returns. Furthermore, GLP greatly decreases the bandwidth usage to a high extent and protects the LBS provider from excessive disclosure of POIs. We discuss the performance and security analysis of the GLP protocol and show that the proposed protocol is secure against partial collusion in a malicious model. With location-based services (LBSs), mobile users are able to ask location-dependent queries and receive the desired information based on their location at any time and from anywhere [1] . For example, a user can ask ''Where is the nearest restaurant to my location?'' or a group of users can ask ''Where is the nearest meeting place that minimizes our aggregate distances?'' [2] .. To benefit from these services, a user must reveal her exact location to the LBS, but this jeopardizes her location privacy [3] . Knowing a user's location could reveal sensitive private information such as her health status, financial status, future activity and political affiliations. Several techniques have been proposed to preserve user location privacy during the use of LBSs [4, 5] , but most of them solely preserve the location privacy of an individual user [4] and do not provide location privacy for a group of users. In this paper, we consider the location privacy problem for a group of users and propose a resource-aware technique to solve it.. We believe that the group location privacy problem is somewhat different from the individual location privacy problem. In particular, there are various privacy issues in the group location privacy problem. As an example, consider a scenario in which a group of users (a working group) needs to urgently meet. They can use an LBS provider to find the nearest meeting place that minimizes their aggregate distances [6] . To get the desired result, each user sends a nearest neighbor (NN) query along with her location to the LBS. The LBS evaluates the set of NN queries (a group of NN queries or an aggregate NN query [6] ) and retrieves the points of interest (POIs) with the smallest aggregate distances from them. Here, the aggregate distance is the total distance of all group members from the meeting location [6] .. We distinguish three major privacy issues in the group location privacy scenario: (i) Preserving the location privacy of each group member inside the group (this is called intragroup location privacy throughout this paper), (ii) preserving the location privacy of each group member from anyone outside the group, including the LBS and outside attackers and (iii) preserving the location privacy of the meeting place. The latter two issues together are called intergroup location privacy. The third privacy issue on its own is needed whenever group members want to have a secret meeting.. According to the above discussion, the focus of group location privacy is on protecting the location privacy for all group members (from users inside and from anyone outside the group) and also on preserving meeting place location privacy (in the case of a secret meeting); individual location privacy aims to protect one user's location privacy. For the above reasons, the techniques of the latter cannot directly be applied to the former; special solutions need to be developed.. In this paper, we aim to preserve the location privacy of all members inside the group and from anyone outside the group. We assume that our group does not intend to have a secret meeting, and thus only provide some brief information about preserving meeting location privacy, leaving the details for a future work.. To the best of our knowledge, Hashem et al. [7] proposed the first solution for preserving group location privacy. In the first phase of this method, each user submits her imprecise location to the LBS and the LBS returns a set of candidate answers with respect to the set of received imprecise locations. In the next phase, Hashem et al. propose a private filtering algorithm that determines the exact result from the answer set without violating members' location privacy.. Although Hashem et al.'s work preserves the location privacy of each user inside and outside the group, it suffers from a high communication cost. It requires each user to send a distinct query (her cloaked region) to the LBS and the LBS to send back a set of candidate answer points that contains the exact result (instead of only sending back the exact result). Further, the set of candidate answers must be refined by the group members to determine the exact answer, which imposes an additional communication cost.. In this paper, we propose a decentralized resource-aware protocol called Group Location Privacy (GLP) to protect location privacy for a group of users while considering communication and computation costs. In GLP, instead of sending several messages, group members collaboratively construct a single message that contains one group location descriptor. This descriptor could be a minimum bounding rectangle (MBR) that encloses all group members or it could be the centroid point of all group members. Using the centroid as the group location descriptor results in some interesting properties. The first one decreases the answer set size, because it is enough for the LBS to return the nearest POI to the centroid in the case of an NN query (or the k nearest POIs in the case of a k-NN query). Secondly, there is no need to refine the answer set because it only contains the exact result. Preserving the privacy of the LBS content is the third property, since the LBS only discloses a single POI in the case of an NN query (or a set of k POIs in the case of a k-NN query); previous works may lead to excessive disclosure of LBS content [2, 3, 7] . Because of these properties, we use the centroid as the group location descriptor.. The rest of the paper is organized as follows: The next section reviews related works in the field of location privacy. Section 3 presents the proposed protocol. The security and efficiency analysis are presented in Section 4. Section 5 compares the proposed protocol with the previous work and Section 6 concludes the paper. In this paper we have considered the problem of supporting location privacy for a group of users who wants to benefit from an LBS and find the nearest meeting place that minimizes their aggregate distance. We have identified the privacy issues for this group scenario and proposed a resource-aware solution -the GLP protocol -to address them. The proposed protocol, which is based on the AV-net protocol and homomorphic encryption, protects the location of all group members from an attacker inside and outside the group. The GLP protocol decreases the number of group queries and the size of the LBS result and also protects the LBS from excessive disclosure of its content. The performance and security analysis of the GLP protocol have been investigated and it has been shown that GLP is secure against partial collusion attacks in a malicious model. The works presented here preserve individual user location privacy based on the group formation idea; Chow et al. [8] were the first to propose a cloaking method based on this technique. In their method, the mobile user forms a group of her peers by contacting them via single-hop or multi-hop communication. Then, she blurs her exact location into a cloaked region that encompasses the entire group. The weakness of Chow's method is that the mobile user can learn the exact location of her peers.. PRIVE [9] and MOBIHIDE [10] , based on the Hilbert Space Filling Curve, assume that users trust their peers. In PRIVE, users are partitioned according to their Hilbert values and the cluster head is responsible for location cloaking. In MOBIHIDE, the mobile user constructs a hash table of other users' locations and cloaks her location by randomly selecting a number of consecutive entries in the table.. Solanas et al. [11] propose a cryptography-based modular method to preserve single-user location privacy. In a simple scheme, a mobile user contacts her peers to learn their masked locations. Then, the centroid point is computed by the user as her fake location. Since locations are masked by adding Gaussian noise with zero mean, users can freely share their locations without trusting their peers. But, if this procedure is applied several times by static users, the user location will be disclosed due to the cancellation of Gaussian noise [11] . As a solution, Solanas et al. extend their scheme by applying a random chain and a privacy homomorphic encryption system, such that each user receives a value from her predecessor in the random chain and then adds her encrypted masked location (with the LBS's public key) to it, then sends the result to another randomly selected peer. This protocol protects user location privacy from the peers and from the LBS. In Solanas et al.'s method, however, if the LBS eavesdrops on the group's internal communication, users' noise-added locations would be revealed in consecutive usages. This factor may lead to reveling the actual location if the user is static, which may or may not be a realistic scenario, depending on the application.. Hu et al. propose a two-phase protocol [1] to preserve individual user location privacy; they apply a group formation technique such that there is no need for users to trust their peers. In the first phase of their method, the mobile user identifies her k peers through proximity information; in the second phase, the MBR of this set of users is constructed through a specialized secure multiparty protocol. This approach is designed for k-anonymity [1] , so although it alleviates the need for peer trusting, it constructs a large cloaked region; having a large cloaked region increases the size of the answer set and communication cost.. As explained in the previous section, Hashem et al.'s method [7] is specially designed for a group location privacy scenario, thus, we describe it here in more detail. The protocol consists of two phases. In the first phase, each user U i registers with the coordinator and gets a query ID (the coordinator is selected randomly before the protocol starts). Then, each U i blurs her exact location l i based on her neighbors' imprecise location [12] and submits her cloaked location R i to the LBS. The coordinator sends a description of the query to the LBS. After receiving all cloaked regions, the LBS returns a set of candidate POIs A (that includes the meeting location) to the coordinator, along with the aggregate maximum d max (p j ) and minimum d min (p j ) distances of each p j 2 A from the cloaked regions.. The second phase privately determines the exact POI through sequentially updating the aggregate maximum and minimum distances of each POI in A with the users' actual distances. This phase can be conducted with or without a coordinator. In the first case, the coordinator sends the LBS result to a randomly selected member U i . The user U i updates d max (p j ) and computes d 0 max ðp j Þ for each p j 2 A by subtracting the value MaxDist(R i , p j ) and adding Dist(l i , p j ), where MaxDist(R i , p j ) is the maximum distance between U i 's cloaked region and a POI p j 2 A, and. After updating the answer set, U i returns it to the coordinator. Then, the coordinator chooses another member and repeats the process until all members update the answer set; finally the coordinator sends the actual result to all members.. In the second case (without the coordinator), the coordinator sends the answer set with a list of unvisited users' identities to a randomly selected member. Then the selected user updates the answer set according to the above equation and passes the updated answer set to a randomly selected user among the unvisited users. After the candidate answer set has been updated by all users, the last user sends the exact result (a POI p 2 A with the minimum aggregate distance) to all group users.. Although Hashem et al.'s method preserves the location privacy of all members, it suffers from high computation and communication costs. The method requires the group to send n distinct nearest neighbor queries and receive a set of candidate answers. Moreover, the cloaking process requires additional communication and computation costs. In particular, computing the imprecise location requires each member to find her k À 1 neighbors and contact them to collect their imprecise locations. Also, the LBS overhead to evaluate a group of NN queries is much higher than that of a single NN query. Furthermore, the private filtering algorithm in Hashem et al.'s method imposes additional computation and communication costs. The protocol is also vulnerable to a partial collusion attack: If the LBS colludes with the coordinator (in the first scenario) or with two users U iÀ1 and U i+1 (in the second scenario), then all members' locations (in the first scenario) or U i 's exact location (in the second scenario) will be revealed. We described this attack in more detail in Section 5.2.. In comparison, the GLP protocol preserves group location privacy in a secure and efficient manner, with lower communication and computation costs. It sends a single NN query instead of n NN queries, and receives the smallest answer set: a single POI in the case of an NN query. In addition, GLP does not need to apply a private filtering algorithm because it receives only a single POI.

O O O O O O B I O B I O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O B I O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O B I O O O O O O O O O B I O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O B I O O O O O O O B I O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O B I O O O O O O O O O O O B I O O O O O O B I O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O B I O O O O O O O O O O O O O O O O O O O B I O O O O O O O O B I O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Modeling a Case of Herding Behavior in a Multi-Player Game The system mentioned in the title belongs to the family of the so-called massively multi-player online social games (MMOSG). It features a scoring system for the elements of the game that is prone to herding effects. We analyze in detail its stationary regime in the thermodynamic limit, when the number of players tends to infinity. In particular, for some classes of input sequences and selection policies, we provide necessary and sufficient conditions for the existence of a complete meanfield-like measure, showing off an interesting condensation phenomenon.

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Towards energy-aware scheduling in data centers using machine learning As energy-related costs have become a major economical factor for IT infrastructures and data-centers, companies and the research community are being challenged to find better and more efficient power-aware resource management strategies. There is a growing interest in "Green" IT and there is still a big gap in this area to be covered. In order to obtain an energy-efficient data center, we propose a framework that provides an intelligent consolidation methodology using different techniques such as turning on/off machines, power-aware consolidation algorithms, and machine learning techniques to deal with uncertain information while maximizing performance. For the machine learning approach, we use models learned from previous system behaviors in order to predict power consumption levels, CPU loads, and SLA timings, and improve scheduling decisions. Our framework is vertical, because it considers from watt consumption to workload features, and cross-disciplinary, as it uses a wide variety of techniques. We evaluate these techniques with a framework that covers the whole control cycle of a real scenario, using a simulation with representative heterogeneous workloads, and we measure the quality of the results according to a set of metrics focused toward our goals, besides traditional policies. The results obtained indicate that our approach is close to the optimal placement and behaves better when the level of uncertainty increases.

O O B O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


The (related-key) impossible boomerang attack and its application to the AES block cipher The Advanced Encryption Standard (AES) is a 128-bit block cipher with a user key of 128, 192 or 256 bits, released by NIST in 2001 as the next-generation data encryption standard for use in the USA. It was adopted as an ISO international standard in 2005. Impossible differential cryptanalysis and the boomerang attack are powerful variants of differential cryptanalysis for analysing the security of a block cipher. In this paper, building on the notions of impossible differential cryptanalysis and the boomerang attack, we propose a new cryptanalytic technique, which we call the impossible boomerang attack, and then describe an extension of this attack which applies in a related-key attack scenario. Finally, we apply the impossible boomerang attack to break 6-round AES with 128 key bits and 7-round AES with 192/256 key bits, and using two related keys we apply the related-key impossible boomerang attack to break 8-round AES with 192 key bits and 9-round AES with 256 key bits. In the two-key related-key attack scenario, our results, which were the first to achieve this amount of attacked rounds, match the best currently known results for AES with 192/256 key bits in terms of the numbers of attacked rounds. The (related-key) impossible boomerang attack is a general cryptanalytic technique, and can potentially be used to cryptanalyse other block ciphers. Differential cryptanalysis, proposed by Biham and Shamir [11] in 1990, is well known as a powerful technique for analysing the security of a block cipher. Typically, to break a block cipher, differential cryptanalysis uses a relatively long differential (i.e. that operating on as many rounds of the cipher as possible) with a probability larger than that for a random permutation that operates on data blocks of the same length. In 1998 and 1999, Knudsen [33] and Biham et al. [3] independently proposed a variant of differential cryptanalysis, known as impossible differential cryptanalysis; it uses a (relatively long) differential with a zero probability, called an impossible differential. In 1999, Wagner [46] proposed the boomerang attack-another variant of differential cryptanalysis, which, unlike differential cryptanalysis, involves something called a boomerang distinguisher that treats a block cipher as two parts and uses two short differentials with relatively large probabilities on the two parts of the cipher, instead of a long differential with a small probability on the entire cipher. Subsequently, several variants of the boomerang attack have been proposed, including the amplified boomerang attack [27] , the rectangle attack [5] , the differential-(bi)linear boomerang attack [7] and the related-key boomerang and rectangle attacks [8, 24, 30] .. The Advanced Encryption Standard (AES) [43] is a 128-bit block cipher with a user key of 128, 192 or 256 bits. It was released by NIST [44] in 2001 as the new-generation data encryption standard for use in the USA, and was adopted as an ISO [25] international standard in 2005. We denote by AES-128/192/256 the versions of AES that respectively use 128, 192 and 256 key bits. Due to its increasingly wide use in many real-life cryptographic applications, AES has always been being analysed against different cryptanalytic techniques, and a variety of cryptanalytic results have been published [1, 8, 10, [12] [13] [14] [15] [16] 18, 19, [21] [22] [23] [24] 26, 29, 36, 40, 45, [48] [49] [50] [51] . In summary, in terms of the numbers of attacked rounds, the most significant results are Biryukov and Khovratovich's related-key (amplified) boomerang attacks on the full-round AES-192/256 [14] , and each attack uses four related keys. (We note that Murphy [42] commented recently that the claims made in [14] by Biryukov and Khovratovich for a related key boomerang analysis of AES must be regarded as unsubstantiated). A related-key attack [2, 28, 31] assumes that the attacker knows or can choose the differences between two or more unknown keys; the more keys are involved, the more difficult and impractical the attack is to conduct. We assume that exhaustive key search (i.e. brute force search) is the best generic attack in the related-key attack scenarios as well as in the one key attack scenario, and an attack is regarded as effective if it is faster (i.e. it has lower time complexity) than exhaustive key search. The two-key related-key attack scenario is the simplest among the related-key attack scenarios. Thus, it is still of great significance to continue investigating the security of AES in the single-key attack scenario and the two-key related-key attack scenario. In the single-key attack scenario, attacks on 7-round AES-128, 8-round AES-192 and 8-round AES-256 [1, 21, 23, 36, 50] are the best currently known results for AES-128/192/256; and in the two-key related-key attack scenario, attacks on 8-round AES-192 and 9-round AES-256 [13, 26, 29, 48, 51] are the best currently known results for AES-192/256. 1 1 When we initially submitted this paper, the related-key impossible differential attack on 8-round AES-256 given in [49] was the best cryptanalytic result for AES-256 in the two-key related-key attack scenario. Recently, Biryukov et al. [13] gave a related-key differential attack on 9-round AES-256 in the two-key related-key attack scenario; and they also described a few cryptanalytic results in a related-subkey attack scenario-a more difficult attack scenario than a related-key attack scenario. In this revised version, we incorporate Biryukov et al.'s 9-round AES-256 attack in the two-key related-key attack scenario, and do not consider the related-subkey attack scenario.. Since the standardization of AES in 2001, few new techniques have been reported, despite the efforts of many cryptanalysts. Like AES, most modern block ciphers are designed to be secure against differential cryptanalysis and linear cryptanalysis [41] . Thus, proposing new cryptanalytic techniques is always desirable in the sense that it provides a better evaluation of the security of a block cipher and also enables more secure ciphers to be designed. Impossible differential cryptanalysis and the boomerang-type attacks (including the boomerang, amplified boomerang and rectangle attacks as well as their variants in a related-key attack scenario) have been used to yield the best currently published cryptanalytic results for a number of state-of-the-art block ciphers [9, 14, 20, 36] . These techniques are thus clearly of importance.. In this paper, inspired by the notions that impossible differential cryptanalysis and the boomerang attack use, we propose a new cryptanalytic technique, which we call the impossible boomerang attack. Such an attack is based on the use of a so-called impossible-boomerang distinguisher, which, like a boomerang distinguisher, treats a block cipher E as two subciphers E 0 • E 1 . Typically, it uses two (or more) differentials with probability 1 for E 0 and two (or more) differentials with probability 1 for E 1 , where the XOR of the intermediate differences of these differentials is not equal to zero (this point makes it different in nature from the boomerang distinguisher). We then describe an extension of this attack that applies in a related-key attack scenario, giving rise to what we call a related-key impossible boomerang attack. Finally, we apply the impossible boomerang attack to break 6-round AES-128 and 7-round AES-192/256 (in the single-key attack scenario), and apply the related-key impossible boomerang attack to break 8-round AES-192 and 9-round AES-256 in the two-key related-key attack scenario. In terms of the numbers of attacked rounds, the impossible boomerang attacks on AES-128/192/256 are one round less than the best currently known cryptanalytic results in the single-key attack scenario, and the related-key impossible boomerang attacks on 8-round AES-192 and 9-round AES-256 match the best currently known results for AES-192/256 in the two-key related-key attack scenario. Table 1 summarises our new and the currently known main cryptanalytic results on AES in the single-key attack scenario and the two-key related-key attack scenario, where CP and RK-CP respectively refer to the required numbers of chosen plaintexts and related-key chosen plaintexts, Enc. refers to the required number of encryption operations of the relevant reduced-round version of AES-128/192/256, and MA refers to the number of memory accesses.. The reminder of the paper is organised as follows. In the next section we briefly describe the notation and the AES block cipher. In Sect. 3 we propose the (related-key) impossible boomerang attack. In Sects. 4 and 5 we present our new cryptanalytic results on AES. Sect. 6 concludes this paper. In this paper we have proposed a new cryptanalytic technique, called the impossible boomerang attack, and have given an extension of this attack which applies in a related-key attack scenario. The impossible boomerang attack can break 6-round AES-128, 7-round AES-192 and 7-round AES-256 in the single-key attack scenario, and the related-key impossible boomerang attack can break 8-round AES-192 and 9-round AES-256 in the two-key related-key attack scenario. Note that trade-off versions between time and memory can be easily obtained from these attacks by using the technique described in [36, 39] . The presented cryptanalytic results suggest a perspective never addressed before to look at the security of AES, exhibiting some merits. The related-key impossible boomerang attack on 9-round AES-256 was the first to achieve this amount of attacked rounds in the two-key related-key attack scenario, and in this particular attack scenario the related-key impossible boomerang attacks on 8-round AES-192 and 9-round AES-256 match the best currently known results for AES-192/256 in terms of the numbers of attacked rounds.. The (related-key) impossible boomerang attack is a general cryptanalytic technique, and can potentially be used to cryptanalyse other block ciphers except AES. Block cipher designers should pay attention to this technique when designing ciphers.

O O O B I O O O O O B B I O O O O B O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O B I O O O O B I O O O O O O B I O O O O O O O O O B I O O B I O O O O O O O O O O O B I O O O O O O O O O O O O B I O O O O O O B I O O O B O O O O O O B O O O O O O O O O O O O O O B I O O O B O O O O O O B O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O B I O O O O B I B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O B I O O O O O O O O O O O O O O O O O O O O O O O O B I O O B I O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O B I O O O O O O O O O B I O O O O O O O O O O O O O O O O B O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O B I O O O O O O O O O O O O O O B O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O B I O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O B I O O O O O B I O O O O O O O O O O O O O O O O O B I O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O B O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B I O O O O O O O O B I O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O B I O O O B I O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B I O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O B B I O O O O O O O O O O


Efficient Encoding Algorithm for Third-Order Spectral-Null Codes Abstract-An efficient algorithm is presented for encoding unconstrained information sequences into a third-order spectral-null code of length n and redundancy 9 log 2 n + O(loglog n). The encoding can be implemented using O(n) integer additions and O(nlog n) counter increments. Let F be the bipolar alphabet f+1; 01g. A word x = (x1; x2; 1 11;xn). in F n is a kth-order spectral-null word (at zero frequency) if the respective real polynomial x1 z + x2z 2 + 111 + xnz n is divisible by (z01) k . We denote by S(n; k) the set of all kth-order spectral-null words in F n . Any subset C of S(n; k) is called a kth-order spectralnull code of length n. The concatenation of any l words in C yields a word in S(nl; k); so, spectral-null codes can be used as block codes with a redundancy of n 0 log 2 jCj bits (per block of length n).. The set S(n; k) is equivalently characterized by S(n; k) = x 2 F n : n j=1 (j + c)`x j = 0;`= 0; 1; . . . ; k01 (1) where c is any real constant (see [5] , and [6, Ch. 9]). First-order spectral-null codes are also known by the names balanced codes, zero-disparity codes, or DC-free codes. There are known efficient encoding algorithms for these codes due to Knuth [3] , Al-Bassam and Bose [1] , and Tallini, Capocelli, and Bose [8] .. Those algorithms result in codes with redundancy at most dlog 2 ne, where n is the code length. By "efficient" we refer to the time and space complexity of the encoding; for example, in one of Knuth's algorithms, the complexity amounts to a lookup table of dlog 2 ne 2 bits and O(n) increments/decrements of a dlog 2 ne-bit counter (as shown in [3] , the space requirement can be eliminated by increasing the redundancy to log 2 n + O(log log n)). The redundancy of S(n; 1) is 1 2 log 2 n + O(1), and such redundancy can be attained by enumerative coding [6, p. 117] . In terms of complexity, however, enumerative coding is less efficient than Knuth's algorithms or the algorithms in [1] and [8] .. Efficient coding algorithms for the second-order spectral-null case were presented in [5] and [7] . Those algorithms have redundancy of 3 log 2 n + O(log log n) bits and time complexity which amounts to O(n) additions of O(log n)-bit integers. Enumerative coding already turns out to be impractical for this case [5] . The redundancy of For higher orders k of spectral null, Karabed and Siegel presented in [2] a coding method based upon finite-state diagrams (see also Monti and Pierobon [4] ). However, since the rate of their construction is strictly less than 1, the resulting redundancy is linear in the code length n. It follows that for any fixed k and sufficiently large n, this redundancy is significantly larger than the upper bound O(2 k 1log n) on the redundancy of S(n; k); this bound is proved in [5] by nonconstructive arguments. A recursive construction is presented in [5] whose redundancy is O(n 10 ), where 0 < k < 1 and lim k!1 k = 0. Yet, this redundancy is still considerably larger than the actual redundancy of S(n; k).. In this correspondence, we present an efficient algorithm for encoding unconstrained sequences into a third-order spectral-null code whose redundancy is logarithmic in the code length. More specifically, for code length n, the redundancy is 9 log 2 n+O(log log n) bits and the encoding complexity is O(n) additions of O(log n)-bit integers and O(n log n) increments/decrements of dlog 2 ne-bit counters.. Statistical moments are useful in a variety of scientific and engineering fields, as witnessed by the wide applicability of correlation functions [1] , and by the increasing volume of research into the study and application of higher order moments, cumulants and higher-order spectra in various areas (see [2] and [3] for two large bibliographies on these and other applications). The key motivation behind using cumulants (which are basically linear combinations of higher order moments) and higher order statistics is that these tend to contain more information (e.g., phase) about the signal under study, and also offer processing domains of higher signal-to-noise ratios (SNR's) than their second-order counterparts. The increase in SNR is only true though whenever the contaminating signals are Gaussian, since their cumulants (order greater than 2) and higher order statistics vanish. Other motivating reasons for using higher order statistics can be found in [3] . In practice and for well-known reasons, moments are computed digitally and this involves an amplitude information loss that increases with decreasing quantization resolution. It is therefore Manuscript received December 7, 1995 of practical interest to seek a characterization of all those quantizer inputs whose finite-order unquantized higher order moments can be exactly recovered from their quantized brethren, regardless of the quantization resolution used. This problem will henceforth be referred to as the exact moment recovery problem. The objective of this correspondence is to seek a solution to this problem which is insensitive to the quantization-induced amplitude information loss, regardless of how coarsely (or finely) coded the quantizer input is. Our study of the exact moment recovery problem was inspired from the classical work of Widrow [4] which, in turn, drew its inspiration from the seminal work of Bennett [5] . The work in [4] popularized the additive model of quantization, i.e., XQ 1 = Q[X] = X + nQ, where Q represents the classical (nonlinear) quantizer and X; XQ; and nQ are the associated input, output, and quantization noise, respectively. As shown in [5] , this model holds well under the conditions of no quantizer overload, fine quantization, and smooth input probability density function, p X (x): In earlier work [6] - [8] , we presented a multidimensional framework for the study of the exact moment recovery problem and used it to rediscover the arcsine (Van Vleck) law. Also, based on the following parametrization of the whole class of uniform quantizers: 2 ) is the shift factor, q the quantization step, and n 2 Z which is the set of integers, we showed that the pth- In an attempt to automatically cancel B p , which depends on the generally unknown unquantized characteristic function W (u), the following theorem (which is an extension of its original counterpart given in [4] ) was derived.. Generalized Quantizing Theorem: Given a general uniform quantizer with shift factor a, input X, step q, and output XQ, if a) the input charateristic function, W (u), is bandlimited, i.e., W (u) = 0 for juj umax (5) b) the quantization fineness, defined by uQ 1 = 2=q, satisfies u Q 2u max (6) 0018-9448/98$10.00 © 1998 IEEE

O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Online health communities Online health communities provide a means for patients and their families to learn about an illness, seek and offer support, and connect with others in similar circumstances. They are supported by a variety of technologies (e.g., email lists, forums, chat rooms) and are hosted by patients, advocacy groups, medical organizations, and corporations. They raise difficult design challenges because of the wide variability of members' medical expertise, the severity of problems due to misinformation, and the need for emotional support. The importance of on-line health communities is evidenced by their popularity, as well as the significant impact they have on the lives of their members. This Special Interest Group (SIG) will explore current trends in online health communities, as well as discuss the socio-technical design challenges and opportunities that they afford. Changes in the health care system coupled with increased infiltration and use of the Internet have resulted in heavier reliance on the Internet for disease and health education. Existing medical websites, such as WebMD [3] , have recognized that they will have more visitors if they offer interactive community features such as web forums and chat rooms. Unfortunately, in many cases these community features are designed by clinicians who do not have an in-depth understanding of how to design for usability and sociability [2] , yet, the criticality of health-related information necessitates careful consideration of design and usability. Further, patients and their families may be under stress and the emotional burden necessitates more careful design and evaluation. Perhaps these challenges are part of the reason that researchers have not yet conclusively demonstrated the health benefits of online support communities [1] .. Although little research has directly measured health benefits, it has pointed to several situations where online health communities aid patients. These benefits include enhanced health literacy, improved quality of life, better decision making, and patients who feel less alone and more empowered [4] . Many online health communities provide a holistic approach to meeting medical, social, and emotional needs; an approach that is difficult to receive through traditional medical consultations. The benefits of online health communities are especially appreciated by individuals with mobility challenges, potentially embarrassing medical conditions, or caretaker responsibilities that may prohibit them from participating in face-to-face medical and emotional support [4] .. For these advantages to accrue, systems must be developed that are accessible, welcoming, easy to navigate and use, and able to help members discern information quality and interact with other participants in meaningful ways. We believe that the successful design of such systems will be facilitated by collaborations among health professionals, informed designers, and patients. Health professionals and patients can help explain the physical and emotional stages that individuals go through once they are diagnosed with a particular disease. Health professionals understand the risks of misinformation and the role that healthcare providers should play. Patients understand the practical information about coping with a disease and the importance of social support and empathy. Systems designers are needed to understand and explain the technological options available to online health communities and the implications of specific design choices.. We hope to bring together a variety of individuals with backgrounds in social science, design, and health for this SIG. Both researchers and practitioners are encouraged to participate, especially those working on online communities, although the appeal will be greatest to people working in or interested in health care. Some CHI attendees may be interested in the SIG due to personal experiences with the use of online communities.

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A canonical model for interactive unawareness Heifetz, Meier and Schipper (2006) introduced a generalized state-space model that allows for non-trivial unawareness among several individuals and strong properties of knowledge. We show that this generalized state-space model arises naturally if states consist of maximally consistent sets of formulas in an appropriate logical formulation.C70, C72, D80, D82. Unawareness refers to lack of conception rather than to lack of information. In standard models of incomplete information, decision makers share the conception of the interactive decision problem but may have asymmetric information. While models of asymmetric information are common in game theory and economics, the modelling of unawareness in interactive decision making proves to be a tricky task. Modica and Rustichini (1994) and Dekel, Lipman and Rustichini (1998) showed that standard state-space models of asymmetric information preclude non-trivial forms of unawareness.. Heifetz, Meier and Schipper (2006) introduced a generalized state-space model that allows for non-trivial unawareness among several individuals and strong properties of knowledge. Such an unawareness structure involves as primitives a lattice of state-spaces ordered according to their strength of "expressive power," and suitable projections among them. The possibility set of one individual in a state of one space may reside in a lower space, while the possibility set of a second individual in one of these possible states may reside in yet a lower space. The former phenomenon reflects the fact that the first individual is unaware of some aspects of reality, and conceives fewer dimensions of the situation than there actually are; the latter reflects the fact that the first individual considers as possible that the second individual is unaware of some aspects of which the first individual is aware. That's how the model captures mutual beliefs about unawareness.. In this paper we substantiate this construction with logical building blocks. Such an investigation of foundations is indeed necessary. Any structure for modelling asymmetric cognition -even if it has the desired properties -begs the question whether the model itself should not be an object for further uncertainties of the individuals. One way to show that a model is comprehensive is to describe in minute detail the beliefs and mutual beliefs of all individuals in each state. If each relevant combination of such beliefs are described in some state of the model, then we are convinced that the phenomena we aim at modelling is captured by our construction.. For the case of knowledge and mutual knowledge, such a detailed substantiation of the beliefs in the standard partition model has been carried out by constructing the canonical model of all maximally-consistent sets of formulas in the S5 system of epistemic logic (Aumann, 1999) . This is the standard propositional logic (with negations, conjunctions and disjunctions of formulas), augmented with a knowledge modality for each individual: For each formula ϕ and each individual i, there is also a formula k i ϕ ("individual i knows ϕ"). The axioms of the system then specify (on top of the standard logical tautologies) that what an individual knows is true, and that the individual knows what she knows and what she ignores. The canonical construction in which the states are the maximally-consistent sets of formulas in this logical system turns out to have a nat-ural partition structure, and the knowledge of events in this partition model reflects exactly the knowledge of formulas in the states. That's how the canonical model is substantiated by the internal structure of its own states.. In this paper we aim at an analogous foundation for the case of unawareness. Two main differences arise.. First, the axiom system has to be amended: An individual knows that she doesn't know some fact only if she is aware of that fact. Our axiom system manifests this feature, and is thus (equivalent to) a multiperson version of axiom systems proposed by Modica and Rustichini (1999) and Halpern (2001) .. Second, in the lattice of spaces of an unawareness structure, only the states in the upper-most space are full descriptions of all aspects of reality relevant to the interaction among the individuals. States in lower spaces are subjective portraits of situations, in the mind of individuals who are unaware of some of these relevant dimensions. Therefore, to construct these subjective descriptions, one has to use a sub-language, with a proper subset of the primitive propositions of the logical syntax.. With these modifications done, we are able to accomplish our mission: The collections of maximallyconsistent sets of formulas (across all sub-languages) constitute an unawareness structure (Theorem 1), in which knowledge of events reflects exactly the knowledge of formulas in states (Theorem 2).. This result entails an important corollary. Logicians are often interested whether an axiom system is sound and complete with respect to a given family of models. Soundness means that every theorem derivable from the axioms obtains in all states of all these models. Completeness means the reverse implication: Every formula that obtains in all states of all the models in the family is provable from the axioms of the system. Our results imply that the axiom system we devised is sound and complete with respect to the family of unawareness structures (Theorem 3). The caveat here is that each space in the lattice of an unawareness structure is associated with a sublanguage (determined by a subset of the primitive propositions), and that higher spaces in the lattice are associated with richer sub-languages. In a state which is a subjective description of reality in the mind of an individual who is unaware of a primitive proposition ϕ, neither ϕ nor ¬ϕ would obtain. If one were to in-sist on a truth value for ϕ in such a state, it would have to be "mu" -a third value, distinct than "true" and "false". This would lead to a three-valued logic, with an extended axiom system that accounts for the third truth value. In parallel work, Halpern and Rêgo (2005) have developed such a three-valued sound and complete axiomatization for the family of our unawareness structures.

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Preserving step edges in low bit rate progressive image compression Abstract-With the growing importance of low-bandwidth applications such as wireless access to the Internet, images are often sent or received at low bit rates. At these bit rates they suffer from significant distortion and artifacts, making it difficult for those viewing the images to understand them. In this paper we present two progressive compression algorithms that focus on preserving the clarity of important image features, such as edges, at compression ratios of 80:1 and more. Both algorithms capture and encode the locations of important edges in the images. The first algorithm then transmits a standard SPIHT bit stream, and at the decoder applies a nonlinear edge-enhancement procedure to improve the clarity of the encoded edges. The second approach uses a modified wavelet transform to "remove" the edges, and encodes the remaining texture information using SPIHT. With both approaches, features in the images that may be important for recognition are well preserved, even at low bit rates.Index Terms-Edge preservation, edge-based wavelet transform, progressive compression. We have presented two progressive image coders intended for use with applications such as fast browsing, or low-bandwidth Internet access, in which users benefit from being able to understand the images early in the progressive bit stream. In fast browsing, for example, if a user is receiving an image, but determines it is not the one she wants, she can terminate the transmission and move on to the next image, saving time. In wireless applications, the transmitter may have knowledge of the available bandwidth, and decide to transmit only the early, low-quality portion of the image. In this case the user may not receive the higher quality image at all, and therefore relies on being able to understand the lower quality version. Both EEIC and FPIC yield images in which, at low bit rates, important edges are clearer than with traditional wavelet-based coders. The improvement is most pronounced for images containing simple, sharply defined objects, large text characters or graphics. For images of these types, the proposed coders may allow improved understanding of image content at low bit rates.

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