6,213 research outputs found
Synthesis of opaque systems with static and dynamic masks
International audienceOpacity is a security property formalizing the absence of secret information leakage and we address in this paper the problem of synthesizing opaque systems. A secret predicate S over the runs of a system G is opaque to an external user having partial observability over G, if s/he can never infer from the observation of a run of G that the run belongs to S. We choose to control the observability of events by adding a device, called a mask, between the system G and the users. We first investigate the case of static partial observability where the set of events the user can observe is fixed a priori by a static mask. In this context, we show that checking whether a system is opaque is PSPACE-complete, which implies that computing an optimal static mask ensuring opacity is also a PSPACE-complete problem. Next, we introduce dynamic partial observability where the set of events the user can observe changes over time and is chosen by a dynamic mask.We show how to check that a system is opaque w.r.t. to a dynamic mask and also address the corresponding synthesis problem: given a system G and secret states S, compute the set of dynamic masks under which S is opaque. Our main result is that the set of such masks can be finitely represented and can be computed in EXPTIME and this is a lower bound. Finally we also address the problem of computing an optimal mask
Opacity with Orwellian Observers and Intransitive Non-interference
Opacity is a general behavioural security scheme flexible enough to account
for several specific properties. Some secret set of behaviors of a system is
opaque if a passive attacker can never tell whether the observed behavior is a
secret one or not. Instead of considering the case of static observability
where the set of observable events is fixed off line or dynamic observability
where the set of observable events changes over time depending on the history
of the trace, we consider Orwellian partial observability where unobservable
events are not revealed unless a downgrading event occurs in the future of the
trace. We show how to verify that some regular secret is opaque for a regular
language L w.r.t. an Orwellian projection while it has been proved undecidable
even for a regular language L w.r.t. a general Orwellian observation function.
We finally illustrate relevancy of our results by proving the equivalence
between the opacity property of regular secrets w.r.t. Orwellian projection and
the intransitive non-interference property
Verification of Information Flow Properties under Rational Observation
Information flow properties express the capability for an agent to infer
information about secret behaviours of a partially observable system. In a
language-theoretic setting, where the system behaviour is described by a
language, we define the class of rational information flow properties (RIFP),
where observers are modeled by finite transducers, acting on languages in a
given family . This leads to a general decidability criterion for
the verification problem of RIFPs on , implying
PSPACE-completeness for this problem on regular languages. We show that most
trace-based information flow properties studied up to now are RIFPs, including
those related to selective declassification and conditional anonymity. As a
consequence, we retrieve several existing decidability results that were
obtained by ad-hoc proofs.Comment: 19 pages, 7 figures, version extended from AVOCS'201
Layered 3D: tomographic image synthesis for attenuation-based light field and high dynamic range displays
We develop tomographic techniques for image synthesis on displays composed of compact volumes of light-attenuating material. Such volumetric attenuators recreate a 4D light field or high-contrast 2D image when illuminated by a uniform backlight. Since arbitrary oblique views may be inconsistent with any single attenuator, iterative tomographic reconstruction minimizes the difference between the emitted and target light fields, subject to physical constraints on attenuation. As multi-layer generalizations of conventional parallax barriers, such displays are shown, both by theory and experiment, to exceed the performance of existing dual-layer architectures. For 3D display, spatial resolution, depth of field, and brightness are increased, compared to parallax barriers. For a plane at a fixed depth, our optimization also allows optimal construction of high dynamic range displays, confirming existing heuristics and providing the first extension to multiple, disjoint layers. We conclude by demonstrating the benefits and limitations of attenuation-based light field displays using an inexpensive fabrication method: separating multiple printed transparencies with acrylic sheets.Dolby Laboratories Inc.Samsung ElectronicsAlfred P. Sloan Foundatio
Probabilistic Opacity for Markov Decision Processes
Opacity is a generic security property, that has been defined on (non
probabilistic) transition systems and later on Markov chains with labels. For a
secret predicate, given as a subset of runs, and a function describing the view
of an external observer, the value of interest for opacity is a measure of the
set of runs disclosing the secret. We extend this definition to the richer
framework of Markov decision processes, where non deterministic choice is
combined with probabilistic transitions, and we study related decidability
problems with partial or complete observation hypotheses for the schedulers. We
prove that all questions are decidable with complete observation and
-regular secrets. With partial observation, we prove that all
quantitative questions are undecidable but the question whether a system is
almost surely non opaque becomes decidable for a restricted class of
-regular secrets, as well as for all -regular secrets under
finite-memory schedulers
Unbiased 4D: Monocular 4D Reconstruction with a Neural Deformation Model
Capturing general deforming scenes is crucial for many computer graphics andvision applications, and it is especially challenging when only a monocular RGBvideo of the scene is available. Competing methods assume dense point tracks,3D templates, large-scale training datasets, or only capture small-scaledeformations. In contrast to those, our method, Ub4D, makes none of theseassumptions while outperforming the previous state of the art in challengingscenarios. Our technique includes two new, in the context of non-rigid 3Dreconstruction, components, i.e., 1) A coordinate-based and implicit neuralrepresentation for non-rigid scenes, which enables an unbiased reconstructionof dynamic scenes, and 2) A novel dynamic scene flow loss, which enables thereconstruction of larger deformations. Results on our new dataset, which willbe made publicly available, demonstrate the clear improvement over the state ofthe art in terms of surface reconstruction accuracy and robustness to largedeformations. Visit the project page https://4dqv.mpi-inf.mpg.de/Ub4D/.<br
FPO++: Efficient Encoding and Rendering of Dynamic Neural Radiance Fields by Analyzing and Enhancing Fourier PlenOctrees
Fourier PlenOctrees have shown to be an efficient representation for
real-time rendering of dynamic Neural Radiance Fields (NeRF). Despite its many
advantages, this method suffers from artifacts introduced by the involved
compression when combining it with recent state-of-the-art techniques for
training the static per-frame NeRF models. In this paper, we perform an
in-depth analysis of these artifacts and leverage the resulting insights to
propose an improved representation. In particular, we present a novel density
encoding that adapts the Fourier-based compression to the characteristics of
the transfer function used by the underlying volume rendering procedure and
leads to a substantial reduction of artifacts in the dynamic model.
Furthermore, we show an augmentation of the training data that relaxes the
periodicity assumption of the compression. We demonstrate the effectiveness of
our enhanced Fourier PlenOctrees in the scope of quantitative and qualitative
evaluations on synthetic and real-world scenes
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