104 research outputs found
Priorities Without Priorities: Representing Preemption in Psi-Calculi
Psi-calculi is a parametric framework for extensions of the pi-calculus with
data terms and arbitrary logics. In this framework there is no direct way to
represent action priorities, where an action can execute only if all other
enabled actions have lower priority. We here demonstrate that the psi-calculi
parameters can be chosen such that the effect of action priorities can be
encoded.
To accomplish this we define an extension of psi-calculi with action
priorities, and show that for every calculus in the extended framework there is
a corresponding ordinary psi-calculus, without priorities, and a translation
between them that satisfies strong operational correspondence. This is a
significantly stronger result than for most encodings between process calculi
in the literature.
We also formally prove in Nominal Isabelle that the standard congruence and
structural laws about strong bisimulation hold in psi-calculi extended with
priorities.Comment: In Proceedings EXPRESS/SOS 2014, arXiv:1408.127
Psi-calculi: a framework for mobile processes with nominal data and logic
The framework of psi-calculi extends the pi-calculus with nominal datatypes
for data structures and for logical assertions and conditions. These can be
transmitted between processes and their names can be statically scoped as in
the standard pi-calculus. Psi-calculi can capture the same phenomena as other
proposed extensions of the pi-calculus such as the applied pi-calculus, the
spi-calculus, the fusion calculus, the concurrent constraint pi-calculus, and
calculi with polyadic communication channels or pattern matching. Psi-calculi
can be even more general, for example by allowing structured channels,
higher-order formalisms such as the lambda calculus for data structures, and
predicate logic for assertions. We provide ample comparisons to related calculi
and discuss a few significant applications. Our labelled operational semantics
and definition of bisimulation is straightforward, without a structural
congruence. We establish minimal requirements on the nominal data and logic in
order to prove general algebraic properties of psi-calculi, all of which have
been checked in the interactive theorem prover Isabelle. Expressiveness of
psi-calculi significantly exceeds that of other formalisms, while the purity of
the semantics is on par with the original pi-calculus.Comment: 44 page
A Fully Abstract Symbolic Semantics for Psi-Calculi
We present a symbolic transition system and bisimulation equivalence for
psi-calculi, and show that it is fully abstract with respect to bisimulation
congruence in the non-symbolic semantics.
A psi-calculus is an extension of the pi-calculus with nominal data types for
data structures and for logical assertions representing facts about data. These
can be transmitted between processes and their names can be statically scoped
using the standard pi-calculus mechanism to allow for scope migrations.
Psi-calculi can be more general than other proposed extensions of the
pi-calculus such as the applied pi-calculus, the spi-calculus, the fusion
calculus, or the concurrent constraint pi-calculus.
Symbolic semantics are necessary for an efficient implementation of the
calculus in automated tools exploring state spaces, and the full abstraction
property means the semantics of a process does not change from the original
Analysing and Comparing Encodability Criteria
Encodings or the proof of their absence are the main way to compare process
calculi. To analyse the quality of encodings and to rule out trivial or
meaningless encodings, they are augmented with quality criteria. There exists a
bunch of different criteria and different variants of criteria in order to
reason in different settings. This leads to incomparable results. Moreover it
is not always clear whether the criteria used to obtain a result in a
particular setting do indeed fit to this setting. We show how to formally
reason about and compare encodability criteria by mapping them on requirements
on a relation between source and target terms that is induced by the encoding
function. In particular we analyse the common criteria full abstraction,
operational correspondence, divergence reflection, success sensitiveness, and
respect of barbs; e.g. we analyse the exact nature of the simulation relation
(coupled simulation versus bisimulation) that is induced by different variants
of operational correspondence. This way we reduce the problem of analysing or
comparing encodability criteria to the better understood problem of comparing
relations on processes.Comment: In Proceedings EXPRESS/SOS 2015, arXiv:1508.06347. The Isabelle/HOL
source files, and a full proof document, are available in the Archive of
Formal Proofs, at
http://afp.sourceforge.net/entries/Encodability_Process_Calculi.shtm
Actor Network Procedures as Psi-calculi for Security Ceremonies
The actor network procedures of Pavlovic and Meadows are a recent graphical
formalism developed for describing security ceremonies and for reasoning about
their security properties. The present work studies the relations of the actor
network procedures (ANP) to the recent psi-calculi framework. Psi-calculi is a
parametric formalism where calculi like spi- or applied-pi are found as
instances. Psi-calculi are operational and largely non-graphical, but have
strong foundation based on the theory of nominal sets and process algebras. One
purpose of the present work is to give a semantics to ANP through psi-calculi.
Another aim was to give a graphical language for a psi-calculus instance for
security ceremonies. At the same time, this work provides more insight into the
details of the ANPs formalization and the graphical representation.Comment: In Proceedings GraMSec 2014, arXiv:1404.163
Modal Logics for Nominal Transition Systems
We define a uniform semantic substrate for a wide variety of process calculi where states and action labels can be from arbitrary nominal sets. A Hennessy-Milner logic for these systems is introduced, and proved adequate for bisimulation equivalence. A main novelty is the use of finitely supported infinite conjunctions. We show how to treat different bisimulation variants such as early, late and open in a systematic way, and make substantial comparisons with related work. The main definitions and theorems have been formalized in Nominal Isabelle
A mechanized proof of loop freedom of the (untimed) AODV routing protocol
The Ad hoc On-demand Distance Vector (AODV) routing protocol allows the nodes
in a Mobile Ad hoc Network (MANET) or a Wireless Mesh Network (WMN) to know
where to forward data packets. Such a protocol is 'loop free' if it never leads
to routing decisions that forward packets in circles. This paper describes the
mechanization of an existing pen-and-paper proof of loop freedom of AODV in the
interactive theorem prover Isabelle/HOL. The mechanization relies on a novel
compositional approach for lifting invariants to networks of nodes. We exploit
the mechanization to analyse several improvements of AODV and show that
Isabelle/HOL can re-establish most proof obligations automatically and identify
exactly the steps that are no longer valid.Comment: The Isabelle/HOL source files, and a full proof document, are
available in the Archive of Formal Proofs, at
http://afp.sourceforge.net/entries/AODV.shtm
Proofs about Network Communication: For Humans and Machines
Many concurrent and distributed systems are safety-critical and therefore
have to provide a high degree of assurance. Important properties of such
systems are frequently proved on the specification level, but implementations
typically deviate from specifications for practical reasons. Machine-checked
proofs of bisimilarity statements are often useful for guaranteeing that
properties of specifications carry over to implementations. In this paper, we
present a way of conducting such proofs with a focus on network communication.
The proofs resulting from our approach are not just machine-checked but also
intelligible for humans.Comment: In Proceedings ICE 2023, arXiv:2308.0892
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