arXiv subjects

R Ramanujam

Publications and source records attributed to R Ramanujam.

5 recordsLinked to original sources

arXiv2025

Protocol insecurity with finitely many sessions and XOR

We present a different proof of the insecurity problem for XOR, solved in by Chevalier, Kuesters, Rusinowitch and Turuani (2005). Our proof uses the notion of typed terms and well-typed proofs, and removes a restriction on the class of protocols to which the [CKRT05] proof applies, by introducing a slightly different (but very natural) notion of protocols, where honest agent sends are derivable from previous receives in the same session.

cs.LO↗

arXiv2024

Solving the insecurity problem for assertions

In the symbolic verification of cryptographic protocols, a central problem is deciding whether a protocol admits an execution which leaks a designated secret to the malicious intruder. Rusinowitch & Turuani (2003) show that, when considering finitely many sessions, this ``insecurity problem'' is NP-complete. Central to their proof strategy is the observation that any execution of a protocol can be simulated by one where the intruder only communicates terms of bounded size. However, when we consider models where, in addition to terms, one can also communicate logical statements about terms, the analysis of the insecurity problem becomes tricky when both these inference systems are considered together. In this paper we consider the insecurity problem for protocols with logical statements that include {\em equality on terms} and {\em existential quantification}. Witnesses for existential quantifiers may be unbounded, and obtaining small witness terms while maintaining equality proofs complicates the analysis considerably. We extend techniques from Rusinowitch & Turuani (2003) to show that this problem is also in NP.

cs.LO↗

arXiv2022

Are Bundles Good Deals for FOML?

Bundled products are often offered as good deals to customers. When we bundle quantifiers and modalities together (as in $\exists x \Box$, $\Diamond \forall x$ etc.) in first-order modal logic (FOML), we get new logical operators whose combinations produce interesting fragments of FOML without any restriction on the arity of predicates, the number of variables, or the modal scope. It is well-known that finding decidable fragments of FOML is hard, so we may ask: do bundled fragments that exploit the distinct expressivity of FOML constitute good deals in balancing the expressivity and complexity? There are a few positive earlier results on some particular fragments. In this paper, we try to fully map the terrain of bundled fragments of FOML in (un)decidability, and in the cases without a definite answer yet, we show that they lack the finite model property. Moreover, whether the logics are interpreted over constant domains (across states/worlds) or increasing domains presents another layer of complexity. We also present the \textit{loosely bundled fragment}, which generalizes the bundles and yet retain decidability (over increasing domain models).

cs.LO↗

arXiv2018

Propositional modal logic with implicit modal quantification

Propositional term modal logic is interpreted over Kripke structures with unboundedly many accessibility relations and hence the syntax admits variables indexing modalities and quantification over them. This logic is undecidable, and we consider a variable-free propositional bi-modal logic with implicit quantification. Thus $[\forall] α$ asserts necessity over all accessibility relations and $[\exists] α$ is classical necessity over some accessibility relation. The logic is associated with a natural bisimulation relation over models and we show that the logic is exactly the bisimulation invariant fragment of a two sorted first order logic. The logic is easily seen to be decidable and admits a complete axiomatization of valid formulas. Moreover the decision procedure extends naturally to the `bundled fragment' of full term modal logic.

cs.LO↗

arXiv2016

Proceedings Fifteenth Conference on Theoretical Aspects of Rationality and Knowledge

The 15th Conference on Theoretical Aspects of Rationality and Knowledge (TARK) took place in Carnegie Mellon University, Pittsburgh, USA from June 4 to 6, 2015. The mission of the TARK conferences is to bring together researchers from a wide variety of fields, including Artificial Intelligence, Cryptography, Distributed Computing, Economics and Game Theory, Linguistics, Philosophy, and Psychology, in order to further our understanding of interdisciplinary issues involving reasoning about rationality and knowledge. These proceedings consist of a subset of the papers / abstracts presented at the TARK conference.

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