In this work, we present the first secure steganographic protocol in the common computational model which, for any communication channel (of sufficiently large min-entropy), is provably secure, reliable, and has nearly optimal bandwidth, but needs super-polynomial time. This solves several open problems in the secret-key steganography in the common computational model. In particular, our result answers

Graph-walking automata (GWA) are abstract finite-state devices that traverse graphs given as an input by following their edges; they have been studied both as a theoretical notion and as a model of pathfinding in robotics. If a graph is regarded as the set of memory configurations of a certain abstract machine, then various families of devices can be described as GWA: such are the two-way finite automata

A Two-Party Authenticated Key Agreement (2-PAKA) protocol facilitates two communicating entities to equally contribute and participate in the establishment of a shared session key. IDentity-based 2-PAKA (ID-2-PAKA) protocols are widely researched, since it eliminates the need for explicit public-key verification using digital certificates. Over the years, identity based 2-PAKA protocols with perfect

Weighted counting problems are a natural generalization of counting problems where a weight is associated with every computational path of polynomial-time non-deterministic Turing machines and the goal is to compute the sum of the weights of all paths (instead of just computing the number of accepting paths). Useful closure properties and plenty of applications make weighted counting problems interesting

Motivated by applications in bioinformatics and image searching, in what follows, we study the classic pattern matching problem in the context of elastic-degenerate strings: the generalised notion of gapped strings. An elastic-degenerate string can been seen as an ordered collection of k strings interleaved by k−1 elastic-degenerate symbols, where each such elastic-degenerate symbol corresponds to

A variant of adaptive arithmetic coding is proposed, adding cryptographic features to this classical compression method. The idea is to perform the updates of the frequency tables for characters of the underlying alphabet selectively, according to some randomly chosen secret key K. We give empirical evidence that with reasonably chosen parameters, the compression performance is not hurt, and discuss

The notion of latent-variable probabilistic context-free derivation of syntactic structures is enhanced to allow heads and unrestricted discontinuities. The chosen formalization covers both constituency parsing and dependency parsing. By the new framework, one obtains a probability distribution over the space of all discontinuous parses. This lends itself to intrinsic evaluation in terms of cross-entropy

The family, L(INDLIN), of languages generated by linear indexed grammars has been studied in the literature. It is known that the Parikh image of every language in L(INDLIN) is semi-linear. However, there are bounded semi-linear languages that are not in L(INDLIN). Here, we look at larger families of (restricted) indexed languages and study their combinatorial and decidability properties, and their

Cyber-Physical Systems (CPSs) are integrations of networking and distributed computing systems with physical processes, where feedback loops allow physical processes to affect computations and vice versa. Although CPSs can be found in several real-world domains (automotive, avionics, energy supply, etc), their verification often relies on simulation test systems rather then formal methodologies. This

We present an alternative Double Description representation for the domain of NNC (not necessarily closed) polyhedra, together with the corresponding Chernikova-like conversion procedure. The representation uses no slack variable at all and provides a solution to a few technical issues caused by the encoding of an NNC polyhedron as a closed polyhedron in a higher dimension space. We then reconstruct

Pushdown automata may contain transitions that are never used in any accepting run of the automaton. We present an algorithm for detecting such useless transitions. A finite automaton that captures the possible stack content during runs of the pushdown automaton, is first constructed in a forward procedure to determine which transitions are reachable, and then employed in a backward procedure to determine

The consensus string (or center string, closest string) of a set S of strings is defined as a string which is within a radius r from all strings in S. It is well-known that the consensus string problem for a finite set of equal-length strings is NP-complete. We study the consensus string problem for multiple languages recognized by finite automata (FAs). We define the consensus string of languages

The Deutsch-Jozsa algorithm is essentially faster than any possible deterministic classical algorithm for solving a promise problem that is in fact a symmetric partial Boolean function, named as the Deutsch-Jozsa problem. The Deutsch-Jozsa problem can be equivalently described as a partial function DJn0:{0,1}n→{0,1} defined as: DJn0(x)=1 for |x|=n/2, DJn0(x)=0 for |x|=0,n, and it is undefined for the

Systems need to be updated to last for a long time in a dynamic environment, and to cope with changing requirements. The update can be performed both statically, by restarting the system, or dynamically. In both the cases, it is important for updates to preserve the desirable properties of the system under update, while possibly enforcing new ones. Here we consider a simple yet general update mechanism

It was conjectured by Černý in 1964 that a synchronizing DFA on n states always has a shortest synchronizing word of length at most (n−1)2, and he gave a sequence of DFAs for which this bound is reached. In this paper, we investigate the role of the alphabet size. For each possible alphabet size, we count DFAs on n≤6 states which synchronize in (n−1)2−e steps, for all e<2⌈n/2⌉. Furthermore, we give

Quantum annealers (QAs) are specialized quantum computers that minimize objective functions over discrete variables by physically exploiting quantum effects. Current QA platforms allow for the optimization of quadratic objectives defined over binary variables (qubits), also known as Ising problems. In the last decade, QA systems as implemented by D-Wave have scaled with Moore-like growth. Current architectures

Modern society is dependent on distributed software systems and to verify them different modelling languages such as mobile ambients were developed. They focus on mobility by allowing both a dynamic network topology as well as the movement of code within the network. To analyse the quality of mobile ambients as a good foundational model for distributed computation, we analyse the level of synchronisation

The unique solution of contractions is a proof technique for (weak) bisimilarity that overcomes certain syntactic limitations of Milner's “unique solution of equations” theorem. This paper presents an overview of a comprehensive formalisation of Milner's Calculus of Communicating Systems (CCS) in the HOL theorem prover (HOL4), with a focus towards the theory of unique solutions of equations and contractions

Motivated by the study of word problems of monoids, we explore two ways of viewing binary relations on X⁎ as languages. We exhibit a hierarchy of classes of binary relations on X⁎, according to the class of languages the relation belongs to and the chosen viewpoint. We give examples of word problems of monoids distinguishing the various classes. Aside from the algebraic interest, these examples demonstrate

A failure detector is a distributed oracle that provides each process with a module that continuously outputs an estimate of which processes in the system have failed. The perfect failure detector provides accurate and eventually complete information about process failures. We show that, in asynchronous failure-prone message-passing systems, perfect failure detection can be achieved using an oracle

Finite-state machines, a simple class of finite Petri nets, were equipped in [16] with an efficiently decidable, truly concurrent, bisimulation-based, behavioral equivalence, called team equivalence, which conservatively extends classic bisimulation equivalence on labeled transition systems and which is checked in a distributed manner, without necessarily building a global model of the overall behavior

Fuzzy extractors derive strong keys from noisy sources. Their security is usually defined information-theoretically, with gaps between known negative results, existential constructions, and polynomial-time constructions. We ask whether using computational security can close these gaps. We show the following: • Negative Result: Noise tolerance in fuzzy extractors is usually achieved using an information

In a casino where arbitrarily small bets are admissible, any betting strategy M can be modified into a saving strategy that, not only is successful on each casino sequence where M is (thus accumulating unbounded wealth inside the casino) but also saves an unbounded capital, by permanently and gradually withdrawing it from the game. Teutsch showed that this is no longer the case when a fixed minimum

We use Kolmogorov complexity methods to give a lower bound on the effective Hausdorff dimension of the point (x,ax+b), given real numbers a, b, and x. We apply our main theorem to a problem in fractal geometry, giving an improved lower bound on the (classical) Hausdorff dimension of generalized sets of Furstenberg type.

We introduce quantitative reductions, a novel technique for structuring the space of quantitative games and solving them that does not rely on a reduction to qualitative games. We show that such reductions exhibit the same desirable properties as their qualitative counterparts and that they additionally retain the optimality of solutions. Moreover, we introduce vertex-ranked games as a general-purpose

Linear Temporal Logic ( ) is one of the most commonly used formalisms for representing and reasoning about temporal properties of computations. Its application domains range from formal verification to artificial intelligence. Many real-time extensions of have been proposed over the years, including Timed Propositional Temporal Logic ( ), that makes it possible to constrain the temporal ordering of

A regular language is almost fully characterized by its right congruence relation. Indeed, a regular language can always be recognized by a dfa isomorphic to the automaton corresponding to its right congruence, henceforth the rightcon automaton. The same does not hold for regular ω-languages. The right congruence of a regular ω-language may not be informative enough; many regular ω-languages have a

Parameterized verification of coverability in broadcast networks with finite state processes has been studied for different types of models and topologies. In this paper, we attempt to develop a theory of broadcast networks in which the processes can be well-structured transition systems. The resulting formalism is called well-structured broadcast networks. For various types of communication topologies

We study multiplayer turn-based games played on a finite directed graph such that each player aims at satisfying an ω-regular Boolean objective. Instead of the well-known notions of Nash equilibrium (NE) and subgame perfect equilibrium (SPE), we focus on the recent notion of weak subgame perfect equilibrium (weak SPE), a refinement of SPE. In this setting, players who deviate can only use the subclass

The usual S5n epistemic model for a multi-agent system is based on a Kripke frame, which is a graph whose edges are labeled with agents that do not distinguish between two states. We propose to uncover the higher dimensional information implicit in this structure, by considering a dual, simplicial complex model. We use dynamic epistemic logic (DEL) to study how an epistemic simplicial complex model

I consider the question of which dependencies are safe for a Team Semantics-based logic FO(D), in the sense that they do not increase its expressive power over sentences when added to it. I show that some dependencies, like totality, non-constancy and non-emptiness, are safe for all logics FO(D), and that other dependencies, like constancy, are not safe for FO(D) for some choices of D despite being

We consider the problem of computing the measure of a regular set of infinite binary trees. While the general case remains unsolved, we show that the measure of a language can be computed when the set is given in one of the following three formalisms: a first-order formula with no descendant relation; a Boolean combination of conjunctive queries (with descendant relation); or by a non-deterministic

We combine computable structure theory and algorithmic learning theory to study learning of families of algebraic structures. Our main result is a model-theoretic characterization of the learning type InfEx≅, consisting of the structures whose isomorphism types can be learned in the limit. We show that a family of structures is InfEx≅-learnable if and only if the structures can be distinguished in

We define and explore a notion of unique prime factorization for constraint functions, and use this as a new tool to prove a complexity classification for counting weighted Eulerian orientation problems with arrow reversal symmetry (ars). We prove that all such problems are either polynomial-time computable or #P-hard. We show that the class of weighted Eulerian orientation problems subsumes all weighted

A multi-stack pushdown system is a natural model of concurrent programs. The basic verification problems are in general undecidable (two stacks suffice to encode a Turing machine), and in the last years, there have been some successful approaches based on under-approximating the system behaviors. In this paper, we propose a restriction of the semantics of the general model such that a symbol that is

We present the link-calculus, an extension of π-calculus, that models interactions that are multiparty, i.e. that may involve more than two processes, mutually exchanging data. Communications are seen as chains of suitably combined links (which record the source and the target ends of each hop of interactions), each contributed by one party. Values are exchanged by means of message tuples, still provided

The PQ-tree is a fundamental data structure that has also been used in comparative genomics to model ancestral genomes with some uncertainty. To quantify the evolution between genomes represented by PQ-trees, in this paper we study two fundamental problems of PQ-tree comparison motivated by this application. First, we show that the problem of comparing two PQ-trees by computing the minimum breakpoint

Well-structured transition systems form a large class of infinite-state systems, for which safety verification is decidable thanks to a generic backward coverability algorithm. However, for several classes of systems, the generic upper bounds one can extract from the algorithm are far from optimal. In particular, in the case of vector addition systems (VAS) and several of their extensions, the known

Interrupt Timed Automata (ITA ) form a subclass of stopwatch automata where reachability and some variants of timed model checking are decidable even in presence of parameters. They are well suited to model and analyze real-time operating systems. Here we extend ITA with polynomial guards and updates, leading to the class of polynomial ITA (PolITA ). We prove that reachability is decidable in 2EXPTIME

This work studies which storage mechanisms in automata permit decidability of the emptiness problem. The question is formalized using valence automata, an abstract model of automata in which the storage mechanism is given by a monoid. For each of a variety of storage mechanisms, one can choose a (typically infinite) monoid M such that valence automata over M are equivalent to (one-way) automata with

A usual way to find positive invariant sets of ordinary differential equations is to restrict the search to predefined finitely generated shapes, such as linear templates, or ellipsoids as in classical quadratic Lyapunov function based approaches. One then looks for generators or parameters for which the corresponding shape has the property that the flow of the ODE goes inwards on its border. But for

We propose a notion of alternating bisimulation for strategic abilities under imperfect information. The bisimulation preserves formulas of ATL⁎ for both the objective and subjective variants of the state-based semantics with imperfect information, which are commonly used in the modeling and verification of multi-agent systems. Furthermore, we apply the theoretical result to the verification of coercion-resistance

We study multi-player turn-based games played on (potentially infinite) directed graphs. An outcome is assigned to every play of the game. Each player has a preference relation on the set of outcomes which allows him to compare plays. We focus on the recently introduced notion of weak subgame perfect equilibrium (weak SPE). This is a variant of the classical notion of SPE, where players who deviate

We develop a game-theoretic semantics (GTS) for the fragment ATL+ of the alternating-time temporal logic ATL⁎, thereby extending the recently introduced GTS for ATL. We show that the game-theoretic semantics is equivalent to the standard compositional semantics of ATL+ with perfect-recall strategies. Based on the new semantics, we provide an analysis of the memory and time resources needed for model

Linear Dynamic Logic on finite traces (LDLF) is a powerful logic for reasoning about the behaviour of concurrent and multi-agent systems. In this paper, we investigate techniques for both the characterisation and verification of equilibria in multi-player games with goals/objectives expressed using logics based on LDLF. This study builds upon a generalisation of Boolean games, a logic-based game model

This paper studies the computation of mixed Nash equilibria in weighted Boolean games. In weighted Boolean games, players aim to maximise the total expected weight of a set of formulas by selecting behavioural strategies, that is, randomisations over the truth assignments for each propositional variable under their unique control. Behavioural strategies thus present a compact representation of mixed

We investigate the existence of various types of equilibria (Nash, subgame perfect, Pareto-optimal, secure) in multi-player multi-outcome infinite sequential games. Our results are transfer theorems: Assuming determinacy for a class of simple two-player win/lose games, we obtain existence results about equilibria in the associated multi-player multi-outcome games.

Image matching is an important task arising in video compression, optical character recognition, medical imaging, watermarking and in many others fields. Given two digital images A and B, image matching determines a transformation f for A such that it most closely resembles B. In this paper, we introduce the first general discretization technique that works for the class of projective transformations

In this contribution we present arbitrary arrow update model logic (AAUML). This is a dynamic epistemic logic or update logic. In update logics, static/basic modalities are interpreted on a given relational model whereas dynamic/update modalities induce transformations (updates) of relational models. In AAUML the update modalities formalize the execution of arrow update models, and there is also a

The Min Label s-t Cut problem is a fundamental problem in combinatorial optimization. This problem comes from many applications in real world, for example, information security and computer networks. We study two linear programs for Min Label s-t Cut, proving that both of them have large integrality gaps, namely, Ω(m) and Ω(m1/3−ϵ) for the respective linear programs, where m is the number of edges

We investigate data-enriched models, like Petri nets with data, where executability of a transition is conditioned by a relation between data values involved. Decidability status of various decision problems in such models may depend on the structure of data domain. According to the WQO Dichotomy Conjecture, if a data domain is homogeneous then it either exhibits a well quasi-order (in which case decidability

Cell-like P systems with symport/antiport rules are computing models inspired by the conservation law, in the sense that they compute by changing the places of objects with respect to the membranes, and not by changing the objects themselves. In this work, a variant of these kinds of membrane systems, called cell-like P systems with evolutional symport/antiport rules, where objects can evolve in the

We present a simple approach for finding all number-conserving two-dimensional cellular automata with the von Neumann neighborhood. We demonstrate the efficiency of this approach by enumerating and describing four special cases: totalistic, outer-totalistic, binary and three-state cellular automata. The last result was not published before. We then proceed to find all reversible two-dimensional number-conserving

Asynchronous Boolean totalistic cellular automata have recently attracted attention as promising models for implementation by reaction-diffusion systems. It is unknown, however, to what extent they are able to conduct computation. In this paper, we introduce the so-called non-camouflage property, which means that a cell's update is insensitive to neighboring states that equal its own state. This property

Cellular automata are discrete dynamical systems with locally defined behaviour, well known as simple models of complex systems. Classically, their dynamics derive from synchronously iterated rules over finite or infinite configurations; however, since for many natural systems to be modelled, asynchrony seems more plausible, asynchronous iteration of the rules has gained a considerable attention in

A set X⊆Σ++ of rectangular pictures over an alphabet Σ is a two-dimensional code if any picture over Σ is tilable in at most one way with pictures in X. Finite strong prefix codes were introduced as a family of decidable two-dimensional codes. We consider infinite strong prefix codes and give a characterization for the maximal ones based on the iterated extensions. Moreover, we study some properties

We consider the asynchronous prediction problem for some automaton as the one consisting in determining, given an initial configuration, if there exists a non-zero probability that some selected site changes its state, when the network is updated picking one site at a time uniformly at random. We show that for the majority automaton, the asynchronous prediction problem is in NC in the two-dimensional

The asynchronous automaton associated with a Boolean network f:{0,1}n→{0,1}n is considered in many applications. It is the finite deterministic automaton with set of states {0,1}n, alphabet {1,…,n}, where the action of letter i on a state x consists in switching the ith component if fi(x)≠xi or doing nothing otherwise. This action is extended to words in the natural way. We then say that a word w fixes

In this paper we study the family of two-state Totalistic Freezing Cellular Automata (TFCA) defined over the triangular and square grids with von Neumann neighborhoods. We say that a Cellular Automaton is Freezing and Totalistic if the active cells remain unchanged, and the new value of an inactive cell depends only on the sum of its active neighbors. We classify all the Cellular Automata in the class

Let G be a group and A a set. A cellular automaton (CA) τ over AG is von Neumann regular (vN-regular) if there exists a CA σ over AG such that τστ=τ, and in such case, σ is called a weak generalised inverse of τ. In this paper, we investigate the vN-regularity of various kinds of CA. First, we establish that, except for trivial cases, there are always CA that are not vN-regular. Second, we obtain a