90,639 research outputs found
A Reduced Semantics for Deciding Trace Equivalence
Many privacy-type properties of security protocols can be modelled using
trace equivalence properties in suitable process algebras. It has been shown
that such properties can be decided for interesting classes of finite processes
(i.e., without replication) by means of symbolic execution and constraint
solving. However, this does not suffice to obtain practical tools. Current
prototypes suffer from a classical combinatorial explosion problem caused by
the exploration of many interleavings in the behaviour of processes.
M\"odersheim et al. have tackled this problem for reachability properties using
partial order reduction techniques. We revisit their work, generalize it and
adapt it for equivalence checking. We obtain an optimisation in the form of a
reduced symbolic semantics that eliminates redundant interleavings on the fly.
The obtained partial order reduction technique has been integrated in a tool
called APTE. We conducted complete benchmarks showing dramatic improvements.Comment: Accepted for publication in LMC
Partial Order Reduction for Security Protocols
Security protocols are concurrent processes that communicate using
cryptography with the aim of achieving various security properties. Recent work
on their formal verification has brought procedures and tools for deciding
trace equivalence properties (e.g., anonymity, unlinkability, vote secrecy) for
a bounded number of sessions. However, these procedures are based on a naive
symbolic exploration of all traces of the considered processes which,
unsurprisingly, greatly limits the scalability and practical impact of the
verification tools.
In this paper, we overcome this difficulty by developing partial order
reduction techniques for the verification of security protocols. We provide
reduced transition systems that optimally eliminate redundant traces, and which
are adequate for model-checking trace equivalence properties of protocols by
means of symbolic execution. We have implemented our reductions in the tool
Apte, and demonstrated that it achieves the expected speedup on various
protocols
Fair Testing
In this paper we present a solution to the long-standing problem of characterising the coarsest liveness-preserving pre-congruence with respect to a full (TCSP-inspired) process algebra. In fact, we present two distinct characterisations, which give rise to the same relation: an operational one based on a De Nicola-Hennessy-like testing modality which we call should-testing, and a denotational one based on a refined notion of failures. One of the distinguishing characteristics of the should-testing pre-congruence is that it abstracts from divergences in the same way as MilnerÂżs observation congruence, and as a consequence is strictly coarser than observation congruence. In other words, should-testing has a built-in fairness assumption. This is in itself a property long sought-after; it is in notable contrast to the well-known must-testing of De Nicola and Hennessy (denotationally characterised by a combination of failures and divergences), which treats divergence as catrastrophic and hence is incompatible with observation congruence. Due to these characteristics, should-testing supports modular reasoning and allows to use the proof techniques of observation congruence, but also supports additional laws and techniques. Moreover, we show decidability of should-testing (on the basis of the denotational characterisation). Finally, we demonstrate its advantages by the application to a number of examples, including a scheduling problem, a version of the Alternating Bit-protocol, and fair lossy communication channel
A Denotational Semantics for Communicating Unstructured Code
An important property of programming language semantics is that they should
be compositional. However, unstructured low-level code contains goto-like
commands making it hard to define a semantics that is compositional. In this
paper, we follow the ideas of Saabas and Uustalu to structure low-level code.
This gives us the possibility to define a compositional denotational semantics
based on least fixed points to allow for the use of inductive verification
methods. We capture the semantics of communication using finite traces similar
to the denotations of CSP. In addition, we examine properties of this semantics
and give an example that demonstrates reasoning about communication and jumps.
With this semantics, we lay the foundations for a proof calculus that captures
both, the semantics of unstructured low-level code and communication.Comment: In Proceedings FESCA 2015, arXiv:1503.0437
PAV ontology: provenance, authoring and versioning
Provenance is a critical ingredient for establishing trust of published
scientific content. This is true whether we are considering a data set, a
computational workflow, a peer-reviewed publication or a simple scientific
claim with supportive evidence. Existing vocabularies such as DC Terms and the
W3C PROV-O are domain-independent and general-purpose and they allow and
encourage for extensions to cover more specific needs. We identify the specific
need for identifying or distinguishing between the various roles assumed by
agents manipulating digital artifacts, such as author, contributor and curator.
We present the Provenance, Authoring and Versioning ontology (PAV): a
lightweight ontology for capturing just enough descriptions essential for
tracking the provenance, authoring and versioning of web resources. We argue
that such descriptions are essential for digital scientific content. PAV
distinguishes between contributors, authors and curators of content and
creators of representations in addition to the provenance of originating
resources that have been accessed, transformed and consumed. We explore five
projects (and communities) that have adopted PAV illustrating their usage
through concrete examples. Moreover, we present mappings that show how PAV
extends the PROV-O ontology to support broader interoperability.
The authors strived to keep PAV lightweight and compact by including only
those terms that have demonstrated to be pragmatically useful in existing
applications, and by recommending terms from existing ontologies when
plausible.
We analyze and compare PAV with related approaches, namely Provenance
Vocabulary, DC Terms and BIBFRAME. We identify similarities and analyze their
differences with PAV, outlining strengths and weaknesses of our proposed model.
We specify SKOS mappings that align PAV with DC Terms.Comment: 22 pages (incl 5 tables and 19 figures). Submitted to Journal of
Biomedical Semantics 2013-04-26 (#1858276535979415). Revised article
submitted 2013-08-30. Second revised article submitted 2013-10-06. Accepted
2013-10-07. Author proofs sent 2013-10-09 and 2013-10-16. Published
2013-11-22. Final version 2013-12-06.
http://www.jbiomedsem.com/content/4/1/3
Changing a semantics: opportunism or courage?
The generalized models for higher-order logics introduced by Leon Henkin, and
their multiple offspring over the years, have become a standard tool in many
areas of logic. Even so, discussion has persisted about their technical status,
and perhaps even their conceptual legitimacy. This paper gives a systematic
view of generalized model techniques, discusses what they mean in mathematical
and philosophical terms, and presents a few technical themes and results about
their role in algebraic representation, calibrating provability, lowering
complexity, understanding fixed-point logics, and achieving set-theoretic
absoluteness. We also show how thinking about Henkin's approach to semantics of
logical systems in this generality can yield new results, dispelling the
impression of adhocness. This paper is dedicated to Leon Henkin, a deep
logician who has changed the way we all work, while also being an always open,
modest, and encouraging colleague and friend.Comment: 27 pages. To appear in: The life and work of Leon Henkin: Essays on
his contributions (Studies in Universal Logic) eds: Manzano, M., Sain, I. and
Alonso, E., 201
- âŠ