12,520 research outputs found
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
A Type Inference Algorithm for Secure Ambients
We consider a type discipline for the Ambient Calculus that associates ambients with security levels and constrains them to be traversed by or opened in ambients of higher security clearance only. We present a bottom-up algorithm that, given an untyped process , computes a minimal set of constraints on security levels such that all actions during runs of are performed without violating the security level priorities. Such an algorithm appears to be a prerequisite to use type systems to ensure security properties in the web scenario
A Mobile Ambients-based Approach for Network Attack Modelling and Simulation
Attack Graphs are an important support for assessment and subsequent improvement of network security. They reveal possible paths an attacker can take to break through security perimeters and traverse a network to reach valuable assets deep inside the network. Although scalability is no longer the main issue, Attack Graphs still have some problems that make them less useful in practice. First, Attack Graphs remain difficult to relate to the network topology. Second, Attack Graphs traditionally only consider the exploitation of vulnerable hosts. Third, Attack Graphs do not rely on automatic identification of potential attack targets. We address these gaps in our MsAMS (Multi-step Attack Modelling and Simulation) tool, based on Mobile Ambients. The tool not only allows the modelling of more static aspects of the network, such as the network topology, but also the dynamics of network attacks. In addition to Mobile Ambients, we use the PageRank algorithm to determine targets and hub scores produced by the HITS (Hypertext Induced Topic Search) algorithm to guide the simulation of an attacker searching for targets
Types for BioAmbients
The BioAmbients calculus is a process algebra suitable for representing
compartmentalization, molecular localization and movements between
compartments. In this paper we enrich this calculus with a static type system
classifying each ambient with group types specifying the kind of compartments
in which the ambient can stay. The type system ensures that, in a well-typed
process, ambients cannot be nested in a way that violates the type hierarchy.
Exploiting the information given by the group types, we also extend the
operational semantics of BioAmbients with rules signalling errors that may
derive from undesired ambients' moves (i.e. merging incompatible tissues).
Thus, the signal of errors can help the modeller to detect and locate unwanted
situations that may arise in a biological system, and give practical hints on
how to avoid the undesired behaviour
A graph semantics for a variant of the ambient calculus more adequate for modeling SOC
In this paper we present a graph semantics of a variant of the well known ambient calculus. The main change of our variant is to extract the mobility commands of the original calculus from the ambient topology. Similar to a previous work of ours, we prove that our encoding have good properties. We strongly believe that this variant would allow us to integrate our graph semantics of our mobile calculus with previous work of us in service oriented computing (SOC). Basically, our work on SOC develops a new graph transformation system which we call temporal symbolic graphs. This new graph formalism is used to give semantics to a design language for SOC developed in an european
project, but it could also be used in connection with other approaches for modeling or specifying service systems.Postprint (published version
A Mobile Ambients-based Approach for Network Attack Modelling and Simulation
Attack Graphs are an important support for assessment and subsequent improvement of network security. They reveal possible paths an attacker can take to break through security perimeters and traverse a network to reach valuable assets deep inside the network. Although scalability is no longer the main issue, Attack Graphs still have some problems that make them less useful in practice. First, Attack Graphs remain difficult to relate to the network topology. Second, Attack Graphs traditionally only consider the exploitation of vulnerable hosts. Third, Attack Graphs do not rely on automatic identification of potential attack targets. We address these gaps in our MsAMS (Multi-step Attack Modelling and Simulation) tool, based on Mobile Ambients. The tool not only allows the modelling of more static aspects of the network, such as the network topology, but also the dynamics of network attacks. In addition to Mobile Ambients, we use the PageRank algorithm to determine targets and hub scores produced by the HITS (Hypertext Induced Topic Search) algorithm to guide the simulation of an attacker searching for targets
A Calculus of Mobility and Communication for Ubiquitous Computing
We propose a Calculus of Mobility and Communication (CMC) for the modelling
of mobility, communication and context-awareness in the setting of ubiquitous
computing. CMC is an ambient calculus with the in and out capabilities of
Cardelli and Gordon's Mobile Ambients. The calculus has a new form of global
communication similar to that in Milner's CCS. In CMC an ambient is tagged with
a set of ports that agents executing inside the ambient are allowed to
communicate on. It also has a new context-awareness feature that allows
ambients to query their location. We present reduction semantics and labelled
transition system semantics of CMC and prove that the semantics coincide. A new
notion of behavioural equivalence is given by defining capability barbed
bisimulation and congruence which is proved to coincide with barbed
bisimulation congruence. The expressiveness of the calculus is illustrated by
two case studies.Comment: In Proceedings WWV 2015, arXiv:1508.0338
Mutual Mobile Membranes with Timers
A feature of current membrane systems is the fact that objects and membranes
are persistent. However, this is not true in the real world. In fact, cells and
intracellular proteins have a well-defined lifetime. Inspired from these
biological facts, we define a model of systems of mobile membranes in which
each membrane and each object has a timer representing their lifetime. We show
that systems of mutual mobile membranes with and without timers have the same
computational power. An encoding of timed safe mobile ambients into systems of
mutual mobile membranes with timers offers a relationship between two
formalisms used in describing biological systems
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