Efficient Batch Verification for UP

Consider a setting in which a prover wants to convince a verifier of the correctness of k NP statements. For example, the prover wants to convince the verifier that k given integers N_1,...,N_k are all RSA moduli (i.e., products of equal length primes). Clearly this problem can be solved by simply having the prover send the k NP witnesses, but this involves a lot of communication. Can interaction help? In particular, is it possible to construct interactive proofs for this task whose communication grows sub-linearly with k? Our main result is such an interactive proof for verifying the correctness of any k UP statements (i.e., NP statements that have a unique witness). The proof-system uses only a constant number of rounds and the communication complexity is k^delta * poly(m), where delta>0 is an arbitrarily small constant, m is the length of a single witness, and the poly term refers to a fixed polynomial that only depends on the language and not on delta. The (honest) prover strategy can be implemented in polynomial-time given access to the k (unique) witnesses. Our proof leverages "interactive witness verification" (IWV), a new type of proof-system that may be of independent interest. An IWV is a proof-system in which the verifier needs to verify the correctness of an NP statement using: (i) a sublinear number of queries to an alleged NP witness, and (ii) a short interaction with a powerful but untrusted prover. In contrast to the setting of PCPs and Interactive PCPs, here the verifier only has access to the raw NP witness, rather than some encoding thereof

Local Proofs Approaching the Witness Length

Interactive oracle proofs (IOPs) are a hybrid between interactive proofs and PCPs. In an IOP the prover is allowed to interact with a verifier (like in an interactive proof) by sending relatively long messages to the verifier, who in turn is only allowed to query a few of the bits that were sent (like in a PCP). In this work we construct, for a large class of NP relations, IOPs in which the communication complexity approaches the witness length. More precisely, for any NP relation for which membership can be decided in polynomial-time and bounded polynomial space (e.g., SAT, Hamiltonicity, Clique, Vertex-Cover, etc.) and for any constant $\gamma>0$, we construct an IOP with communication complexity $(1+\gamma) \cdot n$, where $n$ is the original witness length. The number of rounds as well as the number of queries made by the IOP verifier are constant. This result improves over prior works on short IOPs/PCPs in two ways. First, the communication complexity in these short IOPs is proportional to the complexity of verifying the NP witness, which can be polynomially larger than the witness size. Second, even ignoring the difference between witness length and non-deterministic verification time, prior works incur (at the very least) a large constant multiplicative overhead to the communication complexity. In particular, as a special case, we also obtain an IOP for Circuit-SAT with rate approaching 1: the communication complexity is $(1+\gamma) \cdot t$, for circuits of size $t$ and any constant $\gamma>0$. This improves upon the prior state-of-the-art work of Ben Sasson et al. (ICALP, 2017) who construct an IOP for CircuitSAT with communication length $c \cdot t$ for a large (unspecified) constant $c \geq 1$. Our proof leverages recent constructions of high-rate locally testable tensor codes. In particular, we bypass the barrier imposed by the low rate of multiplication codes (e.g., Reed-Solomon, Reed-Muller or AG codes) - a core component in all known short PCP/IOP constructions

Decentralised computer systems

The architecture of the Web was designed to enable decentralised exchange of information. Early architects envisioned an egalitarian yet organic society thriving in cyberspace. The reality of the Web today, unfortunately, does not bear out these visions: information networks have repeatedly shown a tendency towards consolidation and centralisation with the current Web split between a handful of large corporations. The advent of Bitcoin and successor blockchain networks re-ignited interest in developing alternatives to the centralised Web and paving a way back to the earlier architectural visions for the Web. This has led to immense hype around these technologies with the cryptocurrency market valued at several hundred billions of dollars at the time of writing. With great hype, apparently, come great scams. I start off by analysing the use of Bitcoin as an enabler for crime and then present both technical solutions as well as policy recommendations to mitigate the harm these crimes cause. These policy recommendations then lead us on to look more closely at cryptocurrency's tamer cousin: permissioned blockchains. These systems, while less revolutionary in their premise, nevertheless aim to provide sweeping improvements in the efficiency and transparency of existing enterprise systems. To see whether they work in practice, I present the results of my work in delivering a production permissioned blockchain system to real users. This involves comparing several permissioned blockchain systems, exploring their deficiencies and developing solutions for the most egregious of those. Lastly, I do a deep dive into one of the most persistent technical issues with permissioned blockchains, and decentralised networks in general: the lack of scalability in their consensus mechanisms. I present two novel consensus algorithms that aim to improve upon the state of the art in several ways. The first is designed to enable existing permissioned blockchain networks to scale to thousands of nodes. The second presents an entirely new way of building decentralised consensus systems utilising a trie-based data structure at its core as opposed to the usual linear ledgers used in current systems

Zero-Knowledge Proofs on Secret-Shared Data via Fully Linear PCPs

We introduce and study the notion of fully linear probabilistically checkable proof systems. In such a proof system, the verifier can make a small number of linear queries that apply jointly to the input and a proof vector. Our new type of proof system is motivated by applications in which the input statement is not fully available to any single verifier, but can still be efficiently accessed via linear queries. This situation arises in scenarios where the input is partitioned or secret-shared between two or more parties, or alternatively is encoded using an additively homomorphic encryption or commitment scheme. This setting appears in the context of secure messaging platforms, verifiable outsourced computation, PIR writing, private computation of aggregate statistics, and secure multiparty computation (MPC). In all these applications, there is a need for fully linear proof systems with short proofs. While several efficient constructions of fully linear proof systems are implicit in the interactive proofs literature, many questions about their complexity are open. We present several new constructions of fully linear zero-knowledge proof systems with sublinear proof size for simple or structured languages. For example, in the non-interactive setting of fully linear PCPs, we show how to prove that an input vector $x\in\mathbb{F}^n$ satisfies a single degree-2 equation with a proof of size $O(\sqrt n)$ and $O(\sqrt n)$ linear queries, which we show to be optimal. More generally, for languages that can be recognized by systems of constant-degree equations, we can reduce the proof size to $O(\log n)$ at the cost of $O(\log n)$ rounds of interaction. We use our new proof systems to construct new short zero-knowledge proofs on distributed and secret-shared data. These proofs can be used to improve the performance of many of the example systems mentioned above. Finally, we observe that zero-knowledge proofs on distributed data provide a general-purpose tool for protecting protocols for secure multiparty computation (MPC) against malicious parties. Applying our short fully linear PCPs to natural MPC protocols in the honest-majority setting, we can achieve unconditional protection against malicious parties with sublinear additive communication cost. We use this to improve the communication complexity of recent honest-majority MPC protocols. For instance, using any pseudorandom generator, we obtain a 3-party protocol for Boolean circuits in which the amortized communication cost is only one bit per AND gate per party (compared to 7 bits in the best previous protocol), matching the best known protocols for semi-honest adversaries

The interaction of local and overall buckling of cold-formed stainless steel columns.

Abstract: The objective of this research is to investigate the interaction of local and overall flexural buckling in cold-formed stainless steel columns. Literature study exposes a lack of understanding of this subject and a need for experimental data, particularly on the local-overall interaction buckling of stainless steel open sections. Two separate experimental programs were therefore carried out. The first program included 36 tests on pin-ended lipped channel columns. Three alloys were considered: AISI 304, AISI 430 and 3Cr12. The specimens were designed to fail by local-overall interaction buckling in the inelastic stress range, thus highlighting the non-linear behaviour of stainless steel. Half of the specimens were tested under a concentric load. The other half had the load applied with a nominal eccentricity of Le/1500. The test results demonstrate the imperfection sensitivity of local-overall interaction buckling and illustrate the shift in effective centroid in pin-ended columns with singly symmetric cross-section. The second experimental program studied local-overall interaction buckling in 24 pin-ended stainless steel I-section columns. The specimens consisted of plain channels connected back-to-back using sheet metal screws. Two alloys were considered: AISI 304 and AISI 404. Local and overall imperfections were carefully measured in both experimental programs. Extensive material testing was carried out on the alloys employed in the experimental program, in order to determine tensile and compressive material properties, anisotropic parameters and enhanced corner properties. A detailed finite element model is presented, which includes non-linear material behaviour, anisotropy, increased material properties of the corner areas and local and overall imperfections. The model was verified against the two aforementioned experimental programs and against additional data available in literature on stainless steel SHS columns. The model yielded excellent predictions of the specimen failure mode, ultimate strength and load-deformation behaviour. The finite element model was used to generate additional data for stainless steel columns with lipped channel, plain channel, SHS and I-shaped cross-section, failing by local-overall interaction buckling. The parametric studies covered the practical ranges of overall and cross-sectional slenderness values. The Australian/New Zealand, European and North American standards for stainless steel were evaluated using the available data. The comparison reveals an inability of the design codes to properly account for the interaction effect as the cross-sectional slenderness increases. Predictions are unsafe for I-section columns with intermediate or high cross-sectional slenderness. A direct strength method is proposed for stainless steel columns, accounting for the local-overall interaction effect. The method offers a simple design solution which fits within the framework of the current Australian and North-American standards

Strategies for Combining e-Learning and Serious Games

Analisar as múltiplas valências dos sistemas de aprendizagem em e-learning constitui um desafio. A educação e a comunicação estão em constante (r)evolução. Os fenómenos da globalização afetam de forma direta e/ou indireta a maioria das áreas da atividade humana e os sistemas de ensino aprendizagem não são exceção. A relação entre a utilização de ferramentas e as estratégias digitais é um ponto fulcral desta dissertação. Nesta dissertação doutoral teve como objeto a contextualização e problematização das diferentes estratégias na utilização de game-based na aprendizagem e estratégias de utilização do e-learning. A utilização de jogos sérios no âmbito das aprendizagens digitais em Portugal não é pratica comum no contexto educativo. Assim, esta dissertação foi desenvolvida para a definição de estratégias de utilização dos jogos sérios e e-learning, propondo uma utilização pedagógica dos jogos sérios em sala de aula por forma a motivar e consolidar conhecimentos adquiridos. A construção de jogos sérios com o intuito de corresponder às necessidades foi o objeto de análise da experiência controlada. O jogo sério “Alpha Patrol” foi conceptualizado, desenvolvido e testado sob responsabilidade do Centro de Investigação para Tecnologias Interactivas. O projeto de investigação envolveu diferentes etapas da investigação de forma a adoptar uma estratégia de análise, que por vezes, se mostrou difícil e ingrata. Investigar e desenvolver jogos sérios em Portugal confronta-se com ambientes indiferentes ou mesmo hostis. O preconceito de jogar (em especial no espaço de sala de aula) ainda existe. No estudo de caso que a dissertação apresenta e desenvolve foi decidido que, face a algumas limitações sociais e culturais, o objecto digital a ser analisado apresenta-se uma estrutura híbrida: livro e jogo dele extraído. A experiência controlada permitiu definir os parâmetros sobre o jogo sério criado, os elementos de motivação, a pertinência na utilização de diferentes estratégias como o livro, os quizzes e as medalhas de aprendizagem.To analyze multiple valences of learning systems in e-Learning is a challenge. Education and communication are in constant (r)evolution. The phenomena of globalization affect directly and/or indirectly most areas of human activity and learning educational systems are no exception. This doctoral dissertation focuses on the context and problematization of different strategies in the use of game-based learning and the use of e-learning strategies. The relationship between the use of tools and digital strategies is a key point of this thesis. The use of serious games in the digital learning context in Portugal is not a common practice in the educational context. Thus, this thesis was developed to define the use of elearning and serious games strategies, proposing a pedagogical approach to the use of serious games in the classroom in order to motivate and consolidate knowledge acquisition. The construction of serious games in order to meet the identified needs was the object of analysis of the controlled experiment. The serious game "Alpha Patrol" was conceptualized, developed and tested under the responsibility of the Research Center for Interactive Technologies. The research project involved different stages of the investigation in order to adopt a strategy of analysis, which sometimes proved to be difficult. Research and develop serious games in Portugal is often faced with indifference or even hostile environments. Prejudice to play as a form of knowledge acquisition (especially in the classroom) still exists. With this in mind, in the case study it was decided that the digital object had to present a hybrid structure: a book and the serious game. The controlled experiment allowed to set the parameters for the serious game created, the motivation elements, the relevance of using different strategies like the book, quizzes and learning medals

The Flux-MMF diagram technique and its applications in analysis and comparative evaluation of electrical machines

The thesis describes a new technique, called the flux-MMF diagram technique, for analysis and comparative evaluation of electrical machines. The technique has evolved from the principle of virtual work, and the -i diagram, used commonly in designing switched reluctance machines and relays. Several applications of this technique are demonstrated in the thesis, supported by experimental validation. These are, the prediction of electromagnetic and cogging torque ripple, modelling of the effect of skew on torque and torque ripple, modelling of the variation of torque constant due to saturation, and comparative evaluation of different types of electrical machines. The thesis shows that the technique can be applied successfully in analysis of a wide variety of electrical machines. These include conventional machines such as the DC commutator, PM brushless AC, Interior PM, and the synchronous reluctance machine; as well as non-conventional machines such as the switched reluctance, PM brushless DC, and the doubly-salient PM machine. The technique has been implemented in a finite-element software, with the help of a link program which links the FE software with the dimensioning or sizing software, such as PC-BDC, produced by the SPEED Laboratory. The link program serves as a vital means of shortening the time it takes to analyse a new design in an FE software, by several orders of magnitude. The thesis also describes a new brushless doubly-salient permanent-magnet machine, called the flux-reversal machine. The design and fabrication process, and the experimental results are presented for a prototype single-phase, high-speed flux-reversal generator. The performance analysis of the prototype based on the flux-MMF diagram technique is included, and this validates its capability in analysing new and non-conventional machines, which cannot be analysed using the classical means

Topics in Programming Languages, a Philosophical Analysis through the case of Prolog

[EN]Programming languages seldom find proper anchorage in philosophy of logic, language and science. is more, philosophy of language seems to be restricted to natural languages and linguistics, and even philosophy of logic is rarely framed into programming languages topics. The logic programming paradigm and Prolog are, thus, the most adequate paradigm and programming language to work on this subject, combining natural language processing and linguistics, logic programming and constriction methodology on both algorithms and procedures, on an overall philosophizing declarative status. Not only this, but the dimension of the Fifth Generation Computer system related to strong Al wherein Prolog took a major role. and its historical frame in the very crucial dialectic between procedural and declarative paradigms, structuralist and empiricist biases, serves, in exemplar form, to treat straight ahead philosophy of logic, language and science in the contemporaneous age as well. In recounting Prolog's philosophical, mechanical and algorithmic harbingers, the opportunity is open to various routes. We herein shall exemplify some: - the mechanical-computational background explored by Pascal, Leibniz, Boole, Jacquard, Babbage, Konrad Zuse, until reaching to the ACE (Alan Turing) and EDVAC (von Neumann), offering the backbone in computer architecture, and the work of Turing, Church, Gödel, Kleene, von Neumann, Shannon, and others on computability, in parallel lines, throughly studied in detail, permit us to interpret ahead the evolving realm of programming languages. The proper line from lambda-calculus, to the Algol-family, the declarative and procedural split with the C language and Prolog, and the ensuing branching and programming languages explosion and further delimitation, are thereupon inspected as to relate them with the proper syntax, semantics and philosophical élan of logic programming and Prolog

Structural elucidation of the multidomain response regulator PleD using X-ray crystallography

c-diGMP (bis-(3!5)-cyclic di-guanosine monophosphate) is used extensively in bacteria to control biofilm formation and is lately postulated as a novel secondary messenger. Little is known about the signalling process, nor the control, of this dinucleotide. It is clear, however, that its synthesis is catalysed by the DGC (diguanylate cyclase) domain that contains a conserved GG(D/E)EF sequence motif. Despite its high abundance in bacteria, the structure was until now unknown. The PleD protein from Caulobacter crescentus contains a C-terminal DGC domain, preceded by the input domain D1 and the adaptor domain D2. PleD is a response regulator from the two-component signalling system. The output DGC response relies phosphorylation at the N-terminal D1 input domain. Therefore, the control of c-diGMP signal can be revealed in this multi-domain protein. The objectives of my PhD work are to (1) reveal the structure of DGC domain, (2) understand the catalytic mechanism of DGC, and (3) understand the regulation of the DGC response through the structure of PleD. The crystal structure of PleD has been solved in complex with c-diGMP to 2.7 °A. The fold of the DGC domain is similar to adenylate cyclase, but the proposed nucleotide binding mode is substantially different. The crystal packing has suggested that two DGC domains align in a two-fold symmetric way to catalyse c-diGMP synthesis. Hence, PleD is active as a dimer using D1 and D2 domains for dimerisation. The dimer formation is probably caused by phosphorylation at the D1 domain. In addition, the structure shows that two intercalated products bind at the D2-DGC domain interface. Such binding is thought to serve an allosteric purpose by immobilising DGC domain movements and prevent them from forming the active site. This thesis reports the crystal structure of PleD in complex with cdiGMP, and discusses the implications of the structure on DGC catalysis and on activation and inhibition regulation of DGC activity in PleD. In addition, the thesis describes the preparative investigations and characteri sation that have led to structure determination of PleD. These include the design and screening of PleD constructs, the establishment and optimisation of expression and purification, protein characterisation, crystallisation optimisation, and diffraction data collection