Message Space Research Articles

An experimental analysis of multidimensional cheap talk

We design experimental games that capture the logic of Battaglini's (2002) construction of fully revealing equilibrium in multidimensional cheap talk. Two senders transmit information to a receiver over a 2×2 state space. Despite overall misaligned interests, full revelation is achieved in equilibrium by having the senders truthfully reveal along distinct dimensions. Our experimental findings confirm that more information can be extracted with two senders in a multidimensional setting. The extent to which information is transmitted depends on whether dimensional interests are aligned between a sender and the receiver, the sizes of the message spaces, and the specification of out-of-equilibrium beliefs. While inducing interest alignment on the relevant dimensions and restricting the message spaces facilitated equilibrium play and information transmission, having a fully revealing equilibrium that is supported by implausible beliefs reduced the instances in which the equilibrium was played.

A new public health context to understand male sex work.

BackgroundResearching male sex work offers insight into the sexual lives of men and women while developing a more realistic appreciation for the changing issues associated with male sex work. This type of research is important because it not only reflects a growing and diversifying consumer demand for male sex work, but also because it enables the construction of knowledge that is up-to-date with changing ideas around sex and sexualities.DiscussionThis paper discusses a range of issues emerging in the male sex industry. Notably, globalisation and technology have contributed to the normalisation of male sex work and reshaped the landscape in which the male sex industry operates. As part of this discussion, we review STI and HIV rates among male sex workers at a global level, which are widely disparate and geographically contextual, with rates of HIV among male sex workers ranging from 0% in some areas to 50% in others. The Internet has reshaped the way that male sex workers and clients connect and has been identified as a useful space for safer sex messages and research that seeks out hidden or commonly excluded populations.Future directionsWe argue for a public health context that recognises the emerging and changing nature of male sex work, which means programs and policies that are appropriate for this population group. Online communities relating to male sex work are important avenues for safer sexual messages and unique opportunities to reach often excluded sub-populations of both clients and male sex workers. The changing structure and organisation of male sex work alongside rapidly changing cultural, academic and medical discourses provide new insight but also new challenges to how we conceive the sexualities of men and male sex workers. Public health initiatives must reflect upon and incorporate this knowledge.

CRT-based fully homomorphic encryption over the integers

In 1978, Rivest, Adleman and Dertouzos introduced the basic concept of privacy homomorphism that allows computation on encrypted data without decryption. It was an interesting work whose idea precedes the recent development of fully homomorphic encryption, although actual example schemes proposed in the paper are all susceptible to simple known-plaintext attacks.In this paper, we revisit one of their proposals, in particular the third scheme which is based on the Chinese Remainder Theorem and is ring homomorphic. It is known that only a single pair of known plaintext/ciphertext is needed to break this scheme. However, by exploiting the standard technique to insert an error to a message before encryption, we can cope with this problem. We present a secure modification of their proposal by showing that the proposed scheme is fully homomorphic and secure against the chosen plaintext attacks under the approximate GCD assumption and the sparse subset sum assumption when the message space is restricted to Z2k.Interestingly, the proposed scheme can be regarded as a generalization of the DGHV scheme with larger plaintext space. Our scheme has O∼(λ5) ciphertext expansion overhead while the DGHV has O∼(λ8) for the security parameter λ. When restricted to the homomorphic encryption scheme with depth of O(logλ), the overhead is reduced to O∼(λ). Our scheme can be used in applications requiring a large message space ZQ for logQ=O(λ4), or SIMD style operations on ZQk for logQ=O(λ),k=O(λ3), with O∼(λ5) ciphertext size as in the DGHV.

Another look at XCB

XCB is a tweakable enciphering scheme (TES) which was first proposed in 2004. The scheme was modified in 2007. We call these two versions of XCB as XCBv1 and XCBv2 respectively. XCBv2 was later proposed as a standard for encryption of sector oriented storage media in IEEE-std 1619.2 2010. There is no known proof of security for XCBv1 but the authors provided a concrete security bound for XCBv2 and a "proof" justifying the bound. In this paper we show that XCBv2 is not secure as a TES by showing an easy distinguishing attack on it. For XCBv2 to be secure, the message space should contain only messages whose lengths are multiples of the block length of the block cipher. Even for such restricted message spaces, the bound that the authors claim is not justified. We show this by pointing out some errors in the proof. For XCBv2 on full block messages, we provide a new security analysis. The resulting bound that can be proved is much worse than what has been claimed by the authors. Further, we provide the first concrete security bound for XCBv1, which holds for all message lengths. In terms of known security bounds, both XCBv1 and XCBv2 are worse compared to existing alternative TESs.

Structure-Preserving Signatures and Commitments to Group Elements

A modular approach to constructing cryptographic protocols leads to simple designs but often inefficient instantiations. On the other hand, ad hoc constructions may yield efficient protocols at the cost of losing conceptual simplicity. We suggest a new design paradigm, structure-preserving cryptography, that provides a way to construct modular protocols with reasonable efficiency while retaining conceptual simplicity. A cryptographic scheme over a bilinear group is called structure-preserving if its public inputs and outputs consist of elements from the bilinear groups and their consistency can be verified by evaluating pairing-product equations. As structure-preserving schemes smoothly interoperate with each other, they are useful as building blocks in modular design of cryptographic applications. This paper introduces structure-preserving commitment and signature schemes over bilinear groups with several desirable properties. The commitment schemes include homomorphic, trapdoor and length-reducing commitments to group elements, and the structure-preserving signature schemes are the first ones that yield constant-size signatures on multiple group elements. A structure-preserving signature scheme is called automorphic if the public keys lie in the message space, which cannot be achieved by compressing inputs via a cryptographic hash function, as this would destroy the mathematical structure we are trying to preserve. Automorphic signatures can be used for building certification chains underlying privacy-preserving protocols. Among a vast number of applications of structure-preserving protocols, we present an efficient round-optimal blind-signature scheme and a group signature scheme with an efficient and concurrently secure protocol for enrolling new members.

A General Mechanism Design Methodology for Social Utility Maximization with Linear Constraints

Social utility maximization refers to the process of allocating resources in a way that maximizes the sum of agents' utilities, under the system constraints. Such allocation arises in several problems in the general area of communications, including unicast (and multicast multi-rate) service on the Internet, as well as in applications with (local) public goods, such as power allocation in wireless networks, spectrum allocation, etc. Mechanisms that implement such allocations in Nash equilibrium have also been studied but either they do not possess the full implementation property, or are given in a case-by-case fashion, thus obscuring fundamental understanding of these problems. In this paper we propose a unified methodology for creating mechanisms that fully implement, in Nash equilibria, social utility maximizing functions arising in various contexts where the constraints are convex. Two additional design goals are the focus of this paper: a) the size of the message space scaling linearly with the number of agents (even if agents' types are entire valuation functions), b) allocation being feasible on and off equilibrium.

The Paternalistic Bias of Expert Advice

Using a theoretical model of noisy expert advice, I show that language inflation can be a rational response to the vagueness of language. Experts will tend to overstate their positions to a like‐minded decision maker (DM) and this constitutes a Pareto improvement over sending a sincere message. When the message space is bounded, overstatement may interfere with the DM's ability to aggregate the experts' information, because communication is less precise when the same message is sent for many states of the world. Despite this, I show that experts are willing to send either the most extreme message to the DM, or a partially overstated message, because by doing so the expert can decrease the likelihood the DM makes a suboptimal decision due to his subjective interpretation of the advice. Because the expert inflates his message toward the policy he believes the DM would be better off choosing, rather than sincerely revealing his information, I refer to this behavior as a paternalistic bias.

Practical key‐dependent message chosen‐ciphertext security based on decisional composite residuosity and quadratic residuosity assumptions

AbstractAn encryption scheme is key‐dependent message chosen plaintext attack (KDM‐CPA) secure if it is secure even against an attacker who has access to encryptions of messages that depend on the secret key. Such situations naturally occur in some scenarios such as formal calculus, hard‐disk encryption, or multi‐party protocols. However, up to now, there are not many schemes that achieve KDM‐CPA security, let alone KDM chosen ciphertext attack (KDM‐CCA) security. The constructions proposed by Camenisch, Chandran, and Shoup (Eurocrypt 2009), and Hofheinz (Eurocrypt 2013) are the only two general constructions that can be proved to be KDM‐CCA secure in the standard model. Besides, Qin, Liu, and Huang (ACISP 2013) also presented another concrete implementation. In particular, they showed how to obtain KDM‐CCA security from the classic Cramer–Shoup cryptosystem (based on the decisional Diffie–Hellman assumption) w.r.t. a new ensemble of functions (we call QLH ensemble). Since the Cramer–Shoup scheme has short ciphertext size and higher computational efficiency, they obtain practical KDM‐CCA security w.r.t. a reasonably large ensemble.In this paper, we study the KDM‐CCA security of other cryptosystems proposed by Cramer and Shoup (Eurocrypt 2002). In particular, we prove that the schemes, based on decisional composite residuosity (DCR) and quadratic residuosity (QR) assumptions, respectively, also achieve KDM‐CCA security w.r.t. the QLH ensemble. On the one hand, because the DCR‐based and QR‐based schemes of Cramer et al. are fairly practical, we also obtain practical KDM‐CCA security based on DCR and QR assumptions, respectively. On the other hand, compared with the result of Qin et al., we need not tailor the original schemes of Cramer et al. because themselves have natural “compatibility” for the message space and the secret key space. Copyright © 2014 John Wiley & Sons, Ltd.

The round functions of KASUMI generate the alternating group

Abstract We show that the round functions of the KASUMI block cipher for odd and even round type generate the alternating group on the message space. Moreover, under the assumption of independent round keys, we prove that also the KASUMI two-round functions and the KASUMI encryption functions generate the alternating group.

New order preserving encryption model for outsourced databases in cloud environments

The order of the plaintext remains in the ciphertext, so order-preserving encryption (OPE) scheme is under threat if the adversary is allowed to query for many times. To hide the order in the ciphertext, the only ideal-security OPE scheme (Popa et al., 2013) requires the database server to maintain extra information and realize comparison or range query by user defined functions (UDFs). However, order operations will no longer be performed directly on the ciphertext. It will affect the efficiency and make this scheme to be not suitable for some cases.In this paper, we aim at constructing efficient and programmable OPE scheme for outsourced databases. Firstly, we introduce the system model of outsourced database where OPE scheme will be used, show that ciphertext-only attack is basic and practical security goal. Secondly, we discuss the statistical attack for OPE schemes, point out how to hide data distribution and data frequency is important when designing OPE schemes. Thirdly, we propose a new simple OPE model, which uses message space expansion and nonlinear space split to hide data distribution and frequency and further analyze its security against two kinds of attack in details. Finally, we discuss implementation details including how to use our OPE scheme in the database applications. And we also evaluate its performance through the experiment. The security analysis and performance evaluation show that our OPE scheme is secure enough and more efficient.

Book Reviews

Book Reviews

Book Review: Media Commercialization and Authoritarian Rule in China, by Daniela Stockmann

Media Commercialization and Authoritarian Rule in China. Daniela Stockmann. New York: Cambridge University Press, 2013. 334 pp. $85.50 hbk. $44.95 Kindle.In the past half century, most scholars have abandoned the belief that media alone can bring political change to societies. Stockmann examines China's commercial newspapers and argues that they actually help the Communist regime to stay in power. In their search for readers and advertising, these daily newspapers may empha- size crime, sex, and scandal, she says, but they help stabilize the regime. They provide more space for official messages to the public and allow the government to direct the media with less coercive-and less expensive-controls. Stockmann credits the govern- ment's authoritarian resilience for keeping all the new deregulated media in check.Stockmann's research is impressive. She interviewed forty-six Chinese journalists and reviewed at least sixty Chinese publications (she is fluent in Mandarin). Her 288 pages of text are full of data with impressive statistical analyses, and there are five appendices on research methods plus tables that did not fit into her twelve chapters. Overall, the book would be rewarding but very challenging to a seminar of final semester PhD students. A political scientist at Leiden University in The Netherlands, Stockmann demonstrates command of multiple research methods in what was basi- cally her PhD dissertation at the University of Michigan.The author's concentration on newspapers could raise questions since many Chinese primarily and even exclusively use the Internet and social media for gathering information as well as for communicating with each other. Stockmann argues that daily newspapers are very important in China where 80% of city residents read them. Also, since Internet sites are officially forbidden to develop their own stories, they rely on newspapers for their own news reports. She does admit that in their search for advertising revenue, the commercial newspapers tend to ignore people in rural areas where radio and television are the chief sources of news. Stockmann does not ignore the Internet but mentions it only briefly when discussing particular cases.Stockmann has a great deal of data here, perhaps too much, and her conclusions are cautious. She signals this in early warnings that she only hopes the book expands discussion and adds a dynamic element to the discussion. She accepts that the large number of newspapers in China-1,943 licensed in 2009, down from 2,322 just before the 1989 Tiananmen Square student protests-do provide much more information to the Chinese public. But she says this actually gives the regime greater space for its official view of the world. There is always pressure on editors to delve into scandals that might bring more readers and more advertising, but the editors know the limits. They concentrate on local scandals and get to the national level only when Beijing signals that it is acceptable to do so. In effect, there is a lot of self-censorship by jour- nalists and editors who want to keep their positions. …

The Design of Ambiguous Mechanisms

This paper considers the optimal mechanism design problem of an expected revenue maximizing principal who wants to sell a single unit of a good to an agent who is ambiguity averse in the sense of Gilboa and Schmeidler (1989). We show that the optimal static mechanism is an ambiguous mechanism. An ambiguous mechanism specifies a message space and a set of outcome functions. After showing that (a version of) the Revelation Principle holds in our environment, we give an exact characterization of the (smallest) optimal ambiguous mechanism. If the type set is composed of N (finite) types, then the (smallest) optimal ambiguous mechanism contains N - 1 outcome functions. We show that the share of the surplus that the designer can extract from the agent increases as the type set becomes larger and the probability of each single type decreases. In the limiting case where the agent’s type is drawn from a non-atomic distribution on an interval, the optimal ambiguous mechanism extracts all the rent from the agent.

Persuasive communication when the sender's incentives are uncertain

We study persuasion in a modified Crawford–Sobel sender–receiver game in which the receiver makes a binary decision to accept or reject a good recommended by the sender. The good's quality and the sender's type (neutral or biased) are not observable to the receiver. These alterations yield a simple model and a unique truth-telling equilibrium in which neutral senders who observe different qualities fully separate but can only communicate low quality levels accurately. Biased senders adopt a mixed strategy that can successfully persuade the receiver to accept the good most of the time. When the sender's degree of bias is continuously distributed, a truth-telling equilibrium does not exist. Nonetheless, a partition equilibrium exists for any given number of partitions on the message space.

Group signature implies public-key encryption with non-interactive opening

In this paper, we show that public-key encryption with non-interactive opening (PKENO) can be constructed from an arbitrary group signature (GS) scheme which is secure in the dynamic group setting and provides opening soundness. Moreover, the resulting PKENO construction is efficient if the underlying GS scheme is efficient and the message space of the PKENO scheme is restricted to short messages. Hence, our result not only shows that the existence of this type of GS implies the existence of PKENO, but also that designing a practical GS scheme is as difficult as designing a practical PKENO scheme. Our transform is constructed by carefully investigating the relationship between the functionalities of GS and that of PKENO, and developing a novel (but specific) multiple encryption technique. This multiple encryption technique plays an important role for simultaneously achieving both practical efficiency and security.

AAB Public-Key Cryptosystem - A Practical Implementation of the New Asymmetric

This paper aims to provide a practical implementation one of a probabilistic cipher proposed by M.R.K. Ariffin, M.A. Asbullah and N.A. Abu called as AAβ. We provide details on designing and implementing the AAβ algorithm. Furthermore, to support our understanding by providing a statistical analysis of times taken to implement the key generation, encryption and decryption algorithm for the key sizes 3072, 6144, 9216 and 12288 bits for message spaces of 4n where n = 512, 1024, 1536 and 2048 bits. We show the working of the AAβ algorithm purely from a practical standpoint to justify if it is practically implementable even for large data sets operating on large key sizes.

Cost Share Adjustment Processes for Cooperative Group Decisions About Shared Goods: A Design Approach

For group decision about shared goods, the nature of the shared good and how its cost is to be shared among group members must be determined. Complexity arises from heterogeneity in preferences and endowments and nonlinear cost. To facilitate group decision, this paper proposes special type of group decision support system, a cost share adjustment process (CSAP), in which cost shares are adjusted iteratively via algorithmic rules until unanimity is reached, ideally producing a socially optimal, cost feasible, and fair outcome. In contrast to public good literature, our designs apply for situations of nonlinear cost, with economies of scale and fixed costs. In response to impossibility theorems, a design approach is developed: design elements for CSAPs include message space, cost allocation and adjustment rules, controllers, and incentive rules, with many possibilities for specifying a process. Simulation and economic experiment are employed to compare alternative designs, in particular highlighting the incentive effects of message space. As simulation and experiment both indicate, complicated cost allocation rules for incentive purposes may impede locating group agreement. Instead, economic experiments show that unanimity Approval Voting can mitigate the effects of strategic behavior.

New security notions and relations for public-key encryption

Abstract. Since their introduction, the notions of indistinguishability and non-malleability have been changed and extended by different authors to support different goals. In this paper, we propose new flavors of these notions, investigate their relative strengths with respect to previous notions, and provide the full picture of relationships (i.e., implications and separations) among the security notions for public-key encryption schemes. We take into account the two general security goals of indistinguishability and non-malleability, each in the message space, key space, and hybrid message-key space to find six specific goals, a couple of them, namely complete indistinguishability and key non-malleability, are new. Then for each pair of goals, coming from the indistinguishability or non-malleability classes, we prove either an implication or a separation, completing the full picture of relationships among all these security notions. The implications and separations are respectively supported by formal proofs (i.e., reductions) in the concrete-security framework and by counterexamples.

Designing stable mechanisms for economic environments

We study the design of mechanisms that implement Lindahl or Walrasian allocations and whose Nash equilibria are dynamically stable for a wide class of adaptive dynamics. We argue that supermodularity is not a desirable stability criterion in this mechanism design context, focusing instead on contractive mechanisms. We provide necessary and sufficient conditions for a mechanism to Nash-implement Lindahl or Walrasian allocations, show that these conditions are inconsistent with the contraction property when message spaces are one-dimensional, and then show how to use additional dimensions to achieve dynamic stability while gaining budget balance out of equilibrium.

A full characterization of nash implementation with strategy space reduction

The paper fully characterizes the class of Nash implementable social choice correspondences (SCCs) by mechanisms endowed with Saijo’s message space specification—\(s\)-mechanisms. This class of SCCs is equivalent to the class of Nash implementable SCCs, though any game form involving ‘one less’ preference announcements breaks this equivalence relationship down.