100,168 research outputs found
Observing Success in the Pi-Calculus
A contextual semantics - defined in terms of successful termination and may- and should-convergence - is analyzed in the synchronous pi-calculus with replication and a constant Stop to denote success.
The contextual ordering is analyzed, some nontrivial process equivalences are proved, and proof tools for showing contextual equivalences are provided. Among them are a context lemma and new notions of sound applicative similarities for may- and should-convergence. A further result is that contextual equivalence in the pi-calculus with Stop conservatively extends barbed testing equivalence in the (Stop-free) pi-calculus and thus results on contextual equivalence can be transferred to the (Stop-free) pi-calculus with barbed testing equivalence
On the Two-Point Correlation Function for the Invariant Spin One-Half Heisenberg Chain at Roots of Unity
Using tensor calculus we compute the two-point scalar operators
(TPSO), their averages on the ground-state give the two-point correlation
functions. The TPSOs are identified as elements of the Temperley-Lieb algebra
and a recurrence relation is given for them. We have not tempted to derive the
analytic expressions for the correlation functions in the general case but got
some partial results. For , all correlation functions are
(trivially) zero, for , they are related in the continuum to the
correlation functions of left-handed and right-handed Majorana fields in the
half plane coupled by the boundary condition. In the case , one
gets the correlation functions of Mittag's and Stephen's parafermions for the
three-state Potts model. A diagrammatic approach to compute correlation
functions is also presented.Comment: 19 pages, LaTeX, BONN-HE-93-3
Composing security protocols: from confidentiality to privacy
Security protocols are used in many of our daily-life applications, and our privacy largely depends on their design. Formal verification techniques have proved their usefulness to analyse these protocols, but they become so complex that modular techniques have to be developed. We propose several results to safely compose security protocols. We consider arbitrary primitives modeled using an equational theory, and a rich process algebra close to the applied pi calculus.
Relying on these composition results, we derive some security properties on a protocol from the security analysis performed on each of its sub-protocols individually. We consider parallel composition and the case of key-exchange protocols. Our results apply to deal with confidentiality but also privacy-type properties (e.g. anonymity) expressed using a notion of equivalence. We illustrate the usefulness of our composition results on protocols from the 3G phone application and electronic passport
A criterion for separating process calculi
We introduce a new criterion, replacement freeness, to discern the relative
expressiveness of process calculi. Intuitively, a calculus is strongly
replacement free if replacing, within an enclosing context, a process that
cannot perform any visible action by an arbitrary process never inhibits the
capability of the resulting process to perform a visible action. We prove that
there exists no compositional and interaction sensitive encoding of a not
strongly replacement free calculus into any strongly replacement free one. We
then define a weaker version of replacement freeness, by only considering
replacement of closed processes, and prove that, if we additionally require the
encoding to preserve name independence, it is not even possible to encode a non
replacement free calculus into a weakly replacement free one. As a consequence
of our encodability results, we get that many calculi equipped with priority
are not replacement free and hence are not encodable into mainstream calculi
like CCS and pi-calculus, that instead are strongly replacement free. We also
prove that variants of pi-calculus with match among names, pattern matching or
polyadic synchronization are only weakly replacement free, hence they are
separated both from process calculi with priority and from mainstream calculi.Comment: In Proceedings EXPRESS'10, arXiv:1011.601
Trees from Functions as Processes
Levy-Longo Trees and Bohm Trees are the best known tree structures on the
{\lambda}-calculus. We give general conditions under which an encoding of the
{\lambda}-calculus into the {\pi}-calculus is sound and complete with respect
to such trees. We apply these conditions to various encodings of the
call-by-name {\lambda}-calculus, showing how the two kinds of tree can be
obtained by varying the behavioural equivalence adopted in the {\pi}-calculus
and/or the encoding
On the Distributability of Mobile Ambients
Modern society is dependent on distributed software systems and to verify
them different modelling languages such as mobile ambients were developed. To
analyse the quality of mobile ambients as a good foundational model for
distributed computation, we analyse the level of synchronisation between
distributed components that they can express. Therefore, we rely on earlier
established synchronisation patterns. It turns out that mobile ambients are not
fully distributed, because they can express enough synchronisation to express a
synchronisation pattern called M. However, they can express strictly less
synchronisation than the standard pi-calculus. For this reason, we can show
that there is no good and distributability-preserving encoding from the
standard pi-calculus into mobile ambients and also no such encoding from mobile
ambients into the join-calculus, i.e., the expressive power of mobile ambients
is in between these languages. Finally, we discuss how these results can be
used to obtain a fully distributed variant of mobile ambients.Comment: In Proceedings EXPRESS/SOS 2018, arXiv:1808.08071. Conference version
of arXiv:1808.0159
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