374,685 research outputs found
On Strong and Weak Sustainability, with an Application to Self-Suspending Real-Time Tasks
Motivated by an apparent contradiction regarding whether certain scheduling policies are sustainable, we revisit the topic of sustainability in real-time scheduling and argue that the existing definitions of sustainability should be further clarified and generalized. After proposing a formal, generic sustainability theory, we relax the existing notion of (strongly) sustainable scheduling policy to provide a new classification called weak sustainability. Proving weak sustainability properties allows reducing the number of variables that must be considered in the search of a worst-case schedule, and hence enables more efficient schedulability analyses and testing regimes even for policies that are not (strongly) sustainable. As a proof of concept, and to better understand a model for which many mistakes were found in the literature, we study weak sustainability in the context of dynamic self-suspending tasks, where we formalize a generic suspension model using the Coq proof assistant and provide a machine-checked proof that any JLFP scheduling policy is weakly sustainable with respect to job costs and variable suspension times
On Strong and Weak Sustainability, with an Application to Self-Susp ending Real-Time Tasks
Motivated by an apparent contradiction regarding whether certain scheduling policies are sustainable, we revisit the topic of sustainability in real-time scheduling and argue that the existing definitions of sustainability should be further clarified and generalized. After proposing a formal, generic sustainability theory, we relax the existing notion of (strongly) sustainable scheduling policy to provide a new classification called weak sustainability. Proving weak sustainability properties allows reducing the number of variables that must be considered in the search of a worst-case schedule, and hence enables more efficient schedulability analyses and testing regimes even for policies that are not (strongly) sustainable. As a proof of concept, and to better understand a model for which many mistakes were found in the literature, we study weak sustainability in the context of dynamic self-suspending tasks, where we formalize a generic suspension model using the Coq proof assistant and provide a machine-checked proof that any JLFP scheduling policy is weakly sustainable with respect to job costs and variable suspension times.info:eu-repo/semantics/publishedVersio
HOW FAR AWAY ARE GAMMA-RAY BURSTERS?
The positions of over 1000 gamma-ray bursts detected with the BATSE
experiment on board of the Compton Gamma Ray Observatory are uniformly and
randomly distributed in the sky, with no significant concentration to the
galactic plane or to the galactic center. The strong gamma-ray bursts have an
intensity distribution consistent with a number density independent of distance
in Euclidean space. Weak gamma-ray bursts are relatively rare, indicating that
either their number density is reduced at large distances or that the space in
which they are distributed is non-Euclidean. In other words, we appear to be at
the center of a spherical and bounded distribution of bursters. This is
consistent with the distribution of all objects that are known to be at
cosmological distances (like galaxies and quasars), but inconsistent with the
distribution of any objects which are known to be in our galaxy (like stars and
globular clusters). If the bursters are at cosmological distances then the
weakest bursts should be redshifted, i.e. on average their durations should be
longer and their spectra should be softer than the corresponding quantities for
the strong bursts. There is some evidence for both effects in the BATSE data.
At this time the cosmological distance scale is strongly favored over the
galactic one, but is not proven. A definite proof (or dis-proof) could be
provided with the results of a search for very weak bursts in the Andromeda
galaxy (M31) with an instrument times more sensitive than BATSE.
If the bursters are indeed at cosmological distances then they are the most
luminous sources of electromagnetic radiation known in the universe. At this
time we have no clue as to their nature, even though well over a hundred
suggestions were published in the scientific journals. An experiment providingComment: gziped, uuencoded PostScript with figures, presented at the 75th
Anniversary Astronomical Debate "The Distance Scale to Gamma Ray Bursts", to
appear in PASP; also available through WWW at
http://www.astro.princeton.edu/~library/prep.html
Automated Certification of Authorisation Policy Resistance
Attribute-based Access Control (ABAC) extends traditional Access Control by
considering an access request as a set of pairs attribute name-value, making it
particularly useful in the context of open and distributed systems, where
security relevant information can be collected from different sources. However,
ABAC enables attribute hiding attacks, allowing an attacker to gain some access
by withholding information. In this paper, we first introduce the notion of
policy resistance to attribute hiding attacks. We then propose the tool ATRAP
(Automatic Term Rewriting for Authorisation Policies), based on the recent
formal ABAC language PTaCL, which first automatically searches for resistance
counter-examples using Maude, and then automatically searches for an Isabelle
proof of resistance. We illustrate our approach with two simple examples of
policies and propose an evaluation of ATRAP performances.Comment: 20 pages, 4 figures, version including proofs of the paper that will
be presented at ESORICS 201
PPP-Completeness with Connections to Cryptography
Polynomial Pigeonhole Principle (PPP) is an important subclass of TFNP with
profound connections to the complexity of the fundamental cryptographic
primitives: collision-resistant hash functions and one-way permutations. In
contrast to most of the other subclasses of TFNP, no complete problem is known
for PPP. Our work identifies the first PPP-complete problem without any circuit
or Turing Machine given explicitly in the input, and thus we answer a
longstanding open question from [Papadimitriou1994]. Specifically, we show that
constrained-SIS (cSIS), a generalized version of the well-known Short Integer
Solution problem (SIS) from lattice-based cryptography, is PPP-complete.
In order to give intuition behind our reduction for constrained-SIS, we
identify another PPP-complete problem with a circuit in the input but closely
related to lattice problems. We call this problem BLICHFELDT and it is the
computational problem associated with Blichfeldt's fundamental theorem in the
theory of lattices.
Building on the inherent connection of PPP with collision-resistant hash
functions, we use our completeness result to construct the first natural hash
function family that captures the hardness of all collision-resistant hash
functions in a worst-case sense, i.e. it is natural and universal in the
worst-case. The close resemblance of our hash function family with SIS, leads
us to the first candidate collision-resistant hash function that is both
natural and universal in an average-case sense.
Finally, our results enrich our understanding of the connections between PPP,
lattice problems and other concrete cryptographic assumptions, such as the
discrete logarithm problem over general groups
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