arXiv subjects

Dhruv Nevatia

Publications and source records attributed to Dhruv Nevatia.

4 recordsLinked to original sources

arXiv2026

Policy Change for Treelike Monitors

We study the policy change problem that arises in the runtime verification of long-running systems. The online monitors typically used in this context are generally treelike, in that they maintain substates that monitor subformulae of the target policy. We consider when and how the policy can be changed while the monitored system is running by only exploiting the information stored in the monitor's state. This is relevant, for example, to account for new system functionality or changes in regulatory requirements. We formally define the policy change problem in a general setting, independent of any specific (treelike) monitor implementation. We then show that policy change for past-time metric temporal logic (pMTL) is decidable but has tight non-primitive recursive lower and upper bounds, while with discrete-time semantics it is EXPSPACE-complete.

cs.LO↗

arXiv2024

Reachability Analysis of the Domain Name System

The high complexity of DNS poses unique challenges for ensuring its security and reliability. Despite continuous advances in DNS testing, monitoring, and verification, protocol-level defects still give rise to numerous bugs and attacks. In this paper, we provide the first decision procedure for the DNS verification problem, establishing its complexity as $\mathsf{2ExpTime}$, which was previously unknown. We begin by formalizing the semantics of DNS as a system of recursive communicating processes extended with timers and an infinite message alphabet. We provide an algebraic abstraction of the alphabet with finitely many equivalence classes, using the subclass of semigroups that recognize positive prefix-testable languages. We then introduce a novel generalization of bisimulation for labelled transition systems, weaker than strong bisimulation, to show that our abstraction is sound and complete. Finally, using this abstraction, we reduce the DNS verification problem to the verification problem for pushdown systems. To show the expressiveness of our framework, we model two of the most prominent attack vectors on DNS, namely amplification attacks and rewrite blackholing.

cs.CR↗

arXiv2023

An Automata Theoretic Characterization of Weighted First-Order Logic

Since the 1970s with the work of McNaughton, Papert and Schützenberger, a regular language is known to be definable in the first-order logic if and only if its syntactic monoid is aperiodic. This algebraic characterisation of a fundamental logical fragment has been extended in the quantitative case by Droste and Gastin, dealing with polynomially ambiguous weighted automata and a restricted fragment of weighted first-order logic. In the quantitative setting, the full weighted first-order logic (without the restriction that Droste and Gastin use, about the quantifier alternation) is more powerful than weighted automata, and extensions of the automata with two-way navigation, and pebbles or nested capabilities have been introduced to deal with it. In this work, we characterise the fragment of these extended weighted automata that recognise exactly the full weighted first-order logic, under the condition that automata are polynomially ambiguous.

cs.LO↗

arXiv2021

An Algebraic Characterisation of First-Order Logic with Neighbour

We give an algebraic characterisation of first-order logic with the neighbour relation, on finite words. For this, we consider languages of finite words over alphabets with an involution on them. The natural algebras for such languages are involution semigroups. To characterise the logic, we define a special kind of semidirect product of involution semigroups, called the locally hermitian product. The characterisation theorem for FO with neighbour states that a language is definable in the logic if and only if it is recognised by a locally hermitian product of an aperiodic commutative involution semigroup, and a locally trivial involution semigroup. We then define the notion of involution varieties of languages, namely classes of languages closed under Boolean operations, quotients, involution, and inverse images of involutory morphisms. An Eilenberg-type correspondence is established between involution varieties of languages and pseudovarieties of involution semigroups.

cs.LO↗