Complexity Assumptions Research Articles

Practically secure linear-map vector commitment and its applications

The primitive of vector commitment scheme allows a user to commit to an ordered sequence of messages (i.e., a vector) and later open the commitment at any position subset of the vector. The most important and desirable feature of vector commitment schemes is that the size of the opening proof is sublinear in the length of the committed vector. The original vector commitment scheme has now been extended to support several new functionalities like aggregation, updatability and homomorphism, and has applications ranging from verifiable data streaming to stateless cryptocurrency. Among these extensions, the linear-map vector commitment (LVC) scheme enables a user to open a general linear map evaluated on the committed vector, rather than those messages of the committed vector as in the original vector commitment scheme. However, the existing LVC schemes are only proved to be secure under the idealized assumptions, i.e., using the algebraic group model, which might be unpractical in the real world. To this end, we eliminate the use of algebraic group model, and propose a practically secure LVC construction. Our construction achieves practical security by additionally generating degree proofs for polynomials that enable a verifier to check the degree of polynomials publicly. We prove the security of the proposed LVC construction in the standard model under a q-type complexity assumption over bilinear groups. Moreover, we demonstrate how to use the proposed LVC scheme to construct maintainable vector commitments and verifiable data streaming protocols. The theoretical comparison and experimental results indicate that our proposal provides stronger security guarantee, while being competitive in terms of efficiency.

Privacy-Preserving Decentralized Functional Encryption for Inner Product

To support secure data mining and privacy-preserving computation, partial access and selective computation on encrypted data are desirable. Functional encryption (FE) is a new paradigm of public-key encryption and allows authorized users to compute specific functions on encrypted data without knowing the data. However, in some FE schemes, a trusted central authority (CA) is required to generate secret keys for users according to the description of functions. In this paper, to reduce trust on the CA and protect users' privacy, a privacy-preserving decentralised FE for inner product (PPDFEIP) scheme is proposed where multiple authorities co-exist and work independently without any interaction. Especially, to resist collusion attacks, all secret keys of the same user are tied to his/her global identifier (GID), but authorities cannot know any information of the GID even if they collaborate. We formalize the definition and security model of our PPFEIP scheme, and propose a concrete construction. Furthermore, the proposed scheme is implemented and evaluated. Finally, the security of our PPDFEIP scheme is reduced to well-known complexity assumptions. The novelty is to reduce trust on the CA, protect users' privacy and enable authorized users to compute inner product on encrypted data without compromising confidentiality.

Estimating statistical power for structural equation models in developmental cognitive science: A tutorial in R

Determining the compositional structure and dimensionality of psychological constructs lies at the heart of many research questions in developmental science. Structural equation modeling (SEM) provides a versatile framework for formalizing and estimating the relationships among multiple latent constructs. While the flexibility of SEM can accommodate many complex assumptions on the underlying structure of psychological constructs, it makes a priori estimation of statistical power and required sample size challenging. This difficulty is magnified when comparing non-nested SEMs, which prevents the use of traditional likelihood-ratio tests. Sample size estimates for SEM model fit comparisons typically rely on generic rules of thumb. Such heuristics can be misleading because statistical power in SEM depends on a variety of model properties. Here, we demonstrate a Monte Carlo simulation approach for estimating a priori statistical power for model selection when comparing non-nested models in an SEM framework. We provide a step-by-step guide to this approach based on an example from our memory development research in children.

Fragmentation in One Health policy and practice responses to antimicrobial resistance and the salutary value of collaborative humility

This paper investigates One Health (OH) applied to antimicrobial resistance (AMR) to deepen and nuance its conceptual underpinnings and inform effective implementation. We consider how models of OH and AMR wedded to bioscience assumptions of life obscure biosocial complexity and reinforce the misleading assumption that scientific knowledge of AMR is generated outside social systems. With reference to in-depth interviews with medical practitioners, scientists and policy-makers working on AMR in Australia and the UK, we explore accounts of OH action on AMR. We show that the implementation of OH is subject to some fragmentation due to workforce organisation, funding arrangements and the absence of detailed guidance for translating OH into practice. Despite OH aspirations for transdisciplinary cooperation and innovation, human-centrism and somewhat incommensurable professional and scientific views on OH constrain trust in the policy approach and limit effective action. We discuss how, in some settings, OH action on AMR does resemble policy aspirations when emphasis is placed on collaborative humility, a finding that underlines OH’s biosocial character. We argue for the development of more robust biosocial models of OH to guide its application to AMR in real world settings.

A Survey of Two Verifiable Delay Functions Using Proof of Exponentiation

A verifiable delay function (VDF) is an important tool used for adding delay in decentralized applications. This paper surveys and compares two beautiful verifiable delay functions, one due to Pietrzak, and the other due to Wesolowski, In addition, we provide a new computational proof of security for one of them, present an attack on an incorrect implementation of the other, and compare the complexity assumptions needed for both schemes.

On the Structural Hardness of Answer Set Programming: Can Structure Efficiently Confine the Power of Disjunctions?

Answer Set Programming (ASP) is a generic problem modeling and solving framework with a strong focus on knowledge representation and a rapid growth of industrial applications. So far, the study of complexity resulted in characterizing hardness and determining their sources, fine-grained insights in the form of dichotomy-style results, as well as detailed parameterized complexity landscapes. Unfortunately, for the well-known parameter treewidth disjunctive programs require double-exponential runtime under reasonable complexity assumptions. This quickly becomes out of reach. We deal with the classification of structural parameters for disjunctive ASP on the program's rule structure (incidence graph). First, we provide a polynomial kernel to obtain single-exponential runtime in terms of vertex cover size, despite subset-minimization being not represented in the program’s structure. Then we turn our attention to strictly better structural parameters between vertex cover size and treewidth. Here, we provide double-exponential lower bounds for the most prominent parameters in that range: treedepth, feedback vertex size, and cliquewidth. Based on this, we argue that unfortunately our options beyond vertex cover size are limited. Our results provide an in-depth hardness study, relying on a novel reduction from normal to disjunctive programs, trading the increase of complexity for an exponential parameter compression.

A simple approach for the computation of magnetic characteristics of 4-phase switched reluctance motor

Switched reluctance motor (SRM) is non-linear in nature due to non-uniform air gap between stator and rotor that is produced from doubly salient poles. To control the operation of non-linear motor, a precise modelling of magnetic characteristic is essential. Traditionally magnetic equivalent circuit, finite element method (FEM) and experimental approaches have been used to derive magnetic characteristics of SRM. These methods involve complex computational steps and numerous assumptions for its calculations. To avoid this complexity, a simple approach is suggested in this paper to compute magnetic characteristics of 4-phase SRM. In this approach, SRM phase inductance is measured directly to identify the location of rotor with respect to stator from unaligned to aligned position. Then, single phase of SRM is excited through asymmetric converter and voltage and currents of corresponding phase is recorded with rotor being blocked using indexing head. Later recorded values are used to compute the magnetic characteristics from unaligned to aligned position. The proposed method is carried out using field programmable gate array (FPGA) controlled 8/6, 4-phase SRM. Further, accuracy of obtained magnetic characteristic is verified using FEM. In addition, fidelity of the magnetic characteristic is also validated by developing a dynamic model of SRM in MATLAB/Simulink

Connection between single-layer quantum approximate optimization algorithm interferometry and thermal distribution sampling

The quantum approximate optimization algorithm (QAOA) was originally proposed to find approximate solutions to combinatorial optimization problems on quantum computers. However, the algorithm has also attracted interest for sampling purposes since it was theoretically demonstrated under reasonable complexity assumptions that one layer of the algorithm already engineers a probability distribution beyond what can be simulated by classical computers. In this regard, a recent study has also shown that, in universal Ising models, this global probability distribution resembles pure but thermal-like distributions at a temperature that depends on the internal correlations of the spin model. In this work, through an interferometric interpretation of the algorithm, we extend the theoretical derivation of the amplitudes of the eigenstates and the Boltzmann distributions generated by a single-layer QAOA. We also review the implications of this behavior from practical and fundamental perspectives.

Striking fear into students’ hearts: Unforeseen consequences of prescribing education

Purpose Undergraduate medical education (UGME) has to prepare students to do safety-critical work (notably, to prescribe) immediately after qualifying. Despite hospitals depending on them, medical graduates consistently report feeling unprepared to prescribe and they sometimes harm patients. Research clarifying how to prepare students better could improve healthcare safety. Our aim was to explore how students experienced preparing for one of their commonest prescribing tasks: intravenous fluid therapy (IVFT). Methods Complexity assumptions guided the research, which used a qualitative methodology oriented towards hermeneutic phenomenology. The study design was an uncontrolled and unplanned complex intervention: judicial review of the iatrogenic death of five children due to hyponatraemia in our region had resulted in the recommendation that students’ education in ‘the implementation of important clinical guidelines’ relevant to fluid and electrolyte balance should be intensified. An opportunity sample of 40 final-year medical students drew and gave audio-recorded commentaries on rich pictures. We completed two template analyses: one of participants’ transcribed commentaries on the pictures and one using a novel heuristic to analyse the pictures themselves. We then reconciled the two analyses into a single template. Results There were four themes: affects, teaching and learning, contradictions, and the curriculum as a journey. To explore interconnections between themes, we chose the picture best exemplifying each of the four themes and interpreted the curriculum journey depicted in each of them. These interpretations were grounded in each participant’s picture, verbal account of the picture, and the aggregate findings of the template analysis. Participants’ experiences were influenced by the situated complexity of IVFT. Layered on top of that, contradictions, overlaps, and gaps within the curriculum introduced extraneous complexity. Confusion and apprehension resulted. Conclusions After spending five years preparing to prescribe IVFT, participants felt unprepared to do so. We conclude that intensive teaching had not achieved its avowed goal of improving students’ preparedness for safe practice. Merton’s seminal work on the ‘unanticipated consequences of purposive social action’ suggests that intensive teaching may even have contributed to their unpreparedness.

Attribute hiding subset predicate encryption: Quantum-resistant construction with efficient decryption

Predicate encryption is well studied due to its flexibility in supporting fine-grained access control. In Katz et al. (2018) proposed a predicate encryption for a new predicate family, called subset predicate encryption. In such a scheme, a ciphertext and a private key are associated with sets. A private key can successfully decrypt a ciphertext if and only if the set for the private key is a subset of the set for the ciphertext. However, we found that, all the existing schemes are not able to hide the sets associated to ciphertexts, i.e., the information of receivers will be revealed. To enhance the privacy for receivers, we proposed the first subset predicate encryption schemes with weakly attribute hiding. Moreover, our first scheme is constructed over lattices, which is believed to be secure against quantum computers. The security of our scheme is formally proven in the standard model under well-studied complexity assumptions.

An impossibility theorem in game dynamics

The Nash equilibrium-a combination of choices by the players of a game from which no self-interested player would deviate-is the predominant solution concept in game theory. Even though every game has a Nash equilibrium, it is not known whether there are deterministic behaviors of the players who play a game repeatedly that are guaranteed to converge to a Nash equilibrium of the game from all starting points. If one assumes that the players' behavior is a discrete-time or continuous-time rule whereby the current mixed strategy profile is mapped to the next, this question becomes a problem in the theory of dynamical systems. We apply this theory, and in particular Conley index theory, to prove a general impossibility result: There exist games, for which all game dynamics fail to converge to Nash equilibria from all starting points. The games which help prove this impossibility result are degenerate, but we conjecture that the same result holds, under computational complexity assumptions, for nondegenerate games. We also prove a stronger impossibility result for the solution concept of approximate Nash equilibria: For a set of games of positive measure, no game dynamics can converge to the set of approximate Nash equilibria for a sufficiently small yet substantial approximation bound. Our results establish that, although the notions of Nash equilibrium and its computation-inspired approximations are universally applicable in all games, they are fundamentally incomplete as predictors of long-term player behavior.

수주산업 회계부정 사례를 통한 외부감사인의 책임과 시사점

[Purpose] The order－made production industry, including the construction and shipbuilding industries, recognizes revenue based on the progress rate. Because progress estimates involve complex assumptions and estimates, they have high inherent risk and high audit risk. As a result, accounting fraud often occurs in order－made industries such as construction and shipbuilding. This study analyzes the accounting fraud cases of Company A in the ordermade production industry from 2008 to 2015 to present legal responsibilities for external auditors' poor auditing and implications of the court’s ruling on Company A’s accounting fraud on external audit.
 [Methodology] We conducted a search of court rulings related to Company A’s accounting fraud lawsuit and literature published by relevant supervisory authorities.
 [Findings] First, external auditors must strive to strengthen their competence and independence. Second, the scope of responsibility of the audit team must be made clear. Third, if the audited company’s submission of audit－related data is insufficient it is necessary to increase the differential information value of the audit report by actively considering modifying the audit opinion. Fourth, active communication between the auditor and the audited company is necessary, and after communication, audit risks must be managed by documentation.
 [Implications] By analyzing cases of accounting fraud in the order－made production industry based on court rulings, this study presented how the auditor’s perspective on accounting audits differs from the court’s perspective. In addition, it is different in that it analyzes accounting fraud cases from the auditor’s responsibility perspective and suggests implications.

VPRNet: Voxel-based Efficient and Partial-to-Partial Point Cloud Registration on Mobile Devices

With the popularity of embedded devices such as LIDAR sensors and depth cameras, the resulting point clouds become the main data format for representing the 3D world and spawn various smart mobile applications. A key technology for enabling these applications to furnish high-quality services is real-time point cloud registration on mobile devices, which synthesizes a complete model or a large-scale scene from multiple partial scans. It aims to deliver increasing sensing range, faster 3D reconstruction and more robust robot navigation. Unfortunately, the performance of these applications is limited by the scale and partial loss of raw point cloud frame. The existing solutions for point cloud registration are difficult to deploy on mobile devices due to their complex models and assumptions about point cloud pairs with large overlap, which cause significant delay and inaccuracy. This paper proposes VPRNet - the first voxel-based registration solution that can achieve real-time partial-to-partial registration with competitive registration quality while being more advantageous for large-scale point clouds on mobile devices. We conduct real-world experiments and extensive simulations cross various datasets and platforms to validate the efficacy of VPRNet and further compare the performance with state-of-the-art approaches.

An efficient identity authentication protocol with revocation, tracking and fine-grained access control for electronic medical system

In recent years, due to the spread of infectious diseases such as COVID-19, people begin to use the electronic medical system to obtain remote diagnosis and treatment services, which improves the convenience of people’s lives. However, people are worried that their private information will be compromised when they use the electronic medical system. To solve the above problems, a large number of identity authentication protocols have been designed to protect user privacy. To further provide fine-grained access control, attribute-based cryptography is employed to design identity authentication protocol, however, most existing protocols do not consider the user revocation problem. In this paper, to meet the actual requirements of user revocation in an electronic medical system, an efficient and novel identity authentication protocol with revocation and tracking is designed based on a linear secret sharing scheme. The unforgeability and anonymity of our proposal are formally proved based on the corresponding complexity assumption. Also, both security analysis and performance analysis show that our protocol has many security properties, such as data integrity, confidentiality, non-repudiation, forward and backward secrecy, data freshness, etc. That is, our protocol is secure, efficient, and highly practical.

A redesigned secure and efficient data transaction protocol for mobile payment system

Generally, the secure protocol was proposed from the certificateless signature (CLS) scheme to provide the corresponding security for the actual application. However, for the previous application protocols, most of the underlying CLS schemes cannot have their claimed security, because some proposals cannot resist forgery attacks or the master secret key can be captured by the probabilistic polynomial time adversary. To further address the above problems, we take several previous CLS schemes as instances to make a detailed analysis of the causes of the above security flaws and point out that, in a secure CLS scheme, we should appropriately publish the public parameters. Based on the above analysis, we design an efficient and secure CLS scheme in this paper, and the unforgeability is proved based on the hardness of discrete logarithm complexity assumption through the Forking lemma. Compared with the existing constructions, our new proposal has advantages in communication and computation efficiency but also has higher security. Furthermore, a concrete construction of a certificateless aggregate signature (CLAS) scheme is designed with the above basic CLS scheme to realize efficient verification of multiple signatures. Finally, we further improve the key conditions that need to be paid attention to design a secure CLS scheme.

An Efficient Identity Authentication Scheme With Dynamic Anonymity for VANETs

Nowadays, as an essential technique for intelligent transportation, Vehicular Ad hoc Networks (VANETs) has significantly improved people’s travel experience, providing richer and smarter services for vehicles while ensuring driver safety. However, considering that VANETs are complex, some security challenges still remain, including but not restricted to privacy preserving of vehicles, authentication of messages, limited resources in computational power and network bandwidth. To address these issues, many privacy-preserving identity authentication schemes for VANETs have been proposed recently. However, these schemes still suffer some limitations. First, their computational overheads are heavy due to the complex calculations. Second, some schemes are vulnerable to various security weaknesses, unable to resist normal attacks. Third, in some schemes, the same pseudonym keeps unchanged and it is linked to the corresponding private key of user. The consequence is that if the user wants to change its pseudonym, the corresponding private key must be changed. In order to further solve the above problems, we propose a novel privacy-preserving identity authentication protocol based on certificateless aggregate signature scheme, allowing the user to generate a fuzzy identity to hide her real identity, and the private key can be kept unchanged even if the corresponding pseudonym is updated. Furthermore, to achieve efficiency in computation, bilinear mapping is avoided in our proposed scheme. We prove that our protocol satisfies unforgeability in the random oracle based on a classic complexity assumption. Finally, the security and efficiency analyses demonstrate that our construction enjoys more security features and better performance compared with the existing schemes.

Automation of flow analysis in scleral vessels based on descriptive-associative algorithms

Blood flow reflects the eye's health and is disrupted in many diseases. Many pathological processes take place at the cellular level like as microcirculation of blood in vessels, and the processing of medical images is a difficult recognition task. Existing techniques for measuring blood flow are limited due to the complex assumptions, equipment and calculations requirements. In this paper, we propose a method for determining the blood flow characteristics in eye conjunctiva vessels, such as linear and volumetric blood speed and topological characteristics of the vascular net. The method preprocesses the video to improve the conditions of analysis and then builds an integral optical flow for definition of flow dynamical characteristic of eye vessels. These characteristics make it possible to determine changes in blood flow in eye vessels. We show the efficiency of our method in natural eye vessel scenes. The research provides valuable insights to novices with limited experience in the diagnosis and can serve as a valuable tool for experienced medical professionals.

Tractable Orders for Direct Access to Ranked Answers of Conjunctive Queries

We study the question of when we can provide direct access to the k-th answer to a Conjunctive Query (CQ) according to a specified order over the answers in time logarithmic in the size of the database, following a preprocessing step that constructs a data structure in time quasilinear in database size. Specifically, we embark on the challenge of identifying the tractable answer orderings , that is, those orders that allow for such complexity guarantees. To better understand the computational challenge at hand, we also investigate the more modest task of providing access to only a single answer (i.e., finding the answer at a given position), a task that we refer to as the selection problem , and ask when it can be performed in quasilinear time. We also explore the question of when selection is indeed easier than ranked direct access. We begin with lexicographic orders . For each of the two problems, we give a decidable characterization (under conventional complexity assumptions) of the class of tractable lexicographic orders for every CQ without self-joins. We then continue to the more general orders by the sum of attribute weights and establish the corresponding decidable characterizations, for each of the two problems, of the tractable CQs without self-joins. Finally, we explore the question of when the satisfaction of Functional Dependencies (FDs) can be utilized for tractability and establish the corresponding generalizations of our characterizations for every set of unary FDs.

Two conceptions of absolute generality

What is absolutely unrestricted quantification? We distinguish two theoretical roles and identify two conceptions of absolute generality: maximally strong generality and maximally inclusive generality. We also distinguish two corresponding kinds of absolute domain. A maximally strong domain contains every potential counterexample to a generalisation. A maximally inclusive domain is such that no domain extends it. We argue that both conceptions of absolute generality are legitimate and investigate the relations between them. Although these conceptions coincide in standard settings, we show how they diverge under more complex assumptions about the structure of meaningful predication, such as cumulative type theory. We conclude by arguing that maximally strong generality is the more theoretically valuable conception.

Debiased and thresholded ridge regression for linear models with heteroskedastic and correlated errors

AbstractHigh-dimensional linear models with independent errors have been well-studied. However, statistical inference on a high-dimensional linear model with heteroskedastic, dependent (and possibly nonstationary) errors is still a novel topic. Under such complex assumptions, the paper at hand introduces a debiased and thresholded ridge regression estimator that is consistent, and is able to recover the model sparsity. Moreover, we derive a Gaussian approximation theorem for the estimator, and apply a dependent wild bootstrap algorithm to construct simultaneous confidence interval and hypothesis tests for linear combinations of parameters. Numerical experiments with both real and simulated data show that the proposed estimator has good finite sample performance. Of independent interest is the development of a new class of heteroscedastic, (weakly) dependent, and nonstationary random variables that can be used as a general model for regression errors.