402 research outputs found
Efficient Large-scale Trace Checking Using MapReduce
The problem of checking a logged event trace against a temporal logic
specification arises in many practical cases. Unfortunately, known algorithms
for an expressive logic like MTL (Metric Temporal Logic) do not scale with
respect to two crucial dimensions: the length of the trace and the size of the
time interval for which logged events must be buffered to check satisfaction of
the specification. The former issue can be addressed by distributed and
parallel trace checking algorithms that can take advantage of modern cloud
computing and programming frameworks like MapReduce. Still, the latter issue
remains open with current state-of-the-art approaches.
In this paper we address this memory scalability issue by proposing a new
semantics for MTL, called lazy semantics. This semantics can evaluate temporal
formulae and boolean combinations of temporal-only formulae at any arbitrary
time instant. We prove that lazy semantics is more expressive than standard
point-based semantics and that it can be used as a basis for a correct
parametric decomposition of any MTL formula into an equivalent one with
smaller, bounded time intervals. We use lazy semantics to extend our previous
distributed trace checking algorithm for MTL. We evaluate the proposed
algorithm in terms of memory scalability and time/memory tradeoffs.Comment: 13 pages, 8 figure
Lapex: A Phoswich balloon experiment for hard X-ray astronomy
Satellite and balloon observations have shown that several classes of celestial objects are hard ( 15 keV) energy band with a sensitivity of approx 10 mCrab has been performed with the UCSD/MIT instrument (A4) on board the HEAO 1 satellite. About 70 X-ray sources were detected, including galactic and extragalactic objects. Hard X-ray emission has been detected in the Galaxy from X-ray pulsars. Extragalactic sources of hard X-ray emission include clusters of galaxies, QSOs, BL Lac objects, Seyfert galaxies. The essential characteristics of the Large Area Phoswich Experiment (LAPEX) for crowded sky field observations are described. It has: (1) a broad energy band of operation (20-300 keV); (2) a 3 sigma sensitivity of about 1 mCrab in 10,000 s of live observing time; and (3) imaging capabilities with an angular resolution of about 20'
Non-collaborative Attackers and How and Where to Defend Flawed Security Protocols (Extended Version)
Security protocols are often found to be flawed after their deployment. We
present an approach that aims at the neutralization or mitigation of the
attacks to flawed protocols: it avoids the complete dismissal of the interested
protocol and allows honest agents to continue to use it until a corrected
version is released. Our approach is based on the knowledge of the network
topology, which we model as a graph, and on the consequent possibility of
creating an interference to an ongoing attack of a Dolev-Yao attacker, by means
of non-collaboration actuated by ad-hoc benign attackers that play the role of
network guardians. Such guardians, positioned in strategical points of the
network, have the task of monitoring the messages in transit and discovering at
runtime, through particular types of inference, whether an attack is ongoing,
interrupting the run of the protocol in the positive case. We study not only
how but also where we can attempt to defend flawed security protocols: we
investigate the different network topologies that make security protocol
defense feasible and illustrate our approach by means of concrete examples.Comment: 29 page
A Declarative Framework for Specifying and Enforcing Purpose-aware Policies
Purpose is crucial for privacy protection as it makes users confident that
their personal data are processed as intended. Available proposals for the
specification and enforcement of purpose-aware policies are unsatisfactory for
their ambiguous semantics of purposes and/or lack of support to the run-time
enforcement of policies.
In this paper, we propose a declarative framework based on a first-order
temporal logic that allows us to give a precise semantics to purpose-aware
policies and to reuse algorithms for the design of a run-time monitor enforcing
purpose-aware policies. We also show the complexity of the generation and use
of the monitor which, to the best of our knowledge, is the first such a result
in literature on purpose-aware policies.Comment: Extended version of the paper accepted at the 11th International
Workshop on Security and Trust Management (STM 2015
Robust H-infinity filtering for 2-D systems with intermittent measurements
This paper is concerned with the problem of robust H∞ filtering for uncertain two-dimensional (2-D) systems with intermittent measurements. The parameter uncertainty is assumed to be of polytopic type, and the measurements transmission is assumed to be imperfect, which is modeled by a stochastic variable satisfying the Bernoulli random binary distribution. Our attention is focused on the design of an H∞ filter such that the filtering error system is stochastically stable and preserves a guaranteed H∞ performance. This problem is solved in the parameter-dependent framework, which is much less conservative than the quadratic approach. By introducing some slack matrix variables, the coupling between the positive definite matrices and the system matrices is eliminated, which greatly facilitates the filter design procedure. The corresponding results are established in terms of linear matrix inequalities, which can be easily tested by using standard numerical software. An example is provided to show the effectiveness of the proposed approac
Symbolic Analysis of Identity-Based Protocols
International audienceWe show how the Tamarin tool can be used to model and reason about security protocols using identity-based cryptography, including identity-based encryption and signatures. Although such protocols involve rather different primitives than conventional public-key cryptography , we illustrate how suitable abstractions and Tamarin's support for equational theories can be used to model and analyze realistic industry protocols, either finding flaws or gaining confidence in their security with respect to different classes of adversaries. Technically, we propose two models of identity-based cryptography. First, we formalize an abstract model, based on simple equations, in which verification of realistic protocols is feasible. Second, we formalize a more precise model, leveraging Tamarin's support for bilinear pairing and exclusive-or. This model is much closer to practical realizations of identity-based cryptography, but deduction is substantially more complex. Along the way, we point out the limits of precise modeling and highlight challenges in providing support for equational reasoning. We evaluate our models on an industrial protocol case study, where we find and fix flaws
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