89,242 research outputs found
A Verified Information-Flow Architecture
SAFE is a clean-slate design for a highly secure computer system, with
pervasive mechanisms for tracking and limiting information flows. At the lowest
level, the SAFE hardware supports fine-grained programmable tags, with
efficient and flexible propagation and combination of tags as instructions are
executed. The operating system virtualizes these generic facilities to present
an information-flow abstract machine that allows user programs to label
sensitive data with rich confidentiality policies. We present a formal,
machine-checked model of the key hardware and software mechanisms used to
dynamically control information flow in SAFE and an end-to-end proof of
noninterference for this model.
We use a refinement proof methodology to propagate the noninterference
property of the abstract machine down to the concrete machine level. We use an
intermediate layer in the refinement chain that factors out the details of the
information-flow control policy and devise a code generator for compiling such
information-flow policies into low-level monitor code. Finally, we verify the
correctness of this generator using a dedicated Hoare logic that abstracts from
low-level machine instructions into a reusable set of verified structured code
generators
Faithful Estimation of Dynamics Parameters from CPMG Relaxation Dispersion Measurements
This work examines the robustness of fitting of parameters describing conformational exchange (kex, pa/b, and Δω) processes from CPMG relaxation dispersion data. We have analyzed the equations describing conformational exchange processes for the intrinsic inter-dependence of their parameters that leads to the existence of multiple equivalent solutions, which equally satisfy the experimental data. We have used Monte-Carlo simulations and fitting to the synthetic data sets as well as the direct 3-D mapping of the parameter space of kex, pa/b, and Δω to quantitatively assess the degree of the parameter inter-dependence. The demonstrated high correlation between parameters can preclude accurate dynamics parameter estimation from NMR spin-relaxation data obtained at a single static magnetic field. The strong parameter inter-dependence can readily be overcome through acquisition of spin-relaxation data at more than one static magnetic field thereby allowing accurate assessment of conformational exchange properties
General rules for bosonic bunching in multimode interferometers
We perform a comprehensive set of experiments that characterize bosonic
bunching of up to 3 photons in interferometers of up to 16 modes. Our
experiments verify two rules that govern bosonic bunching. The first rule,
obtained recently in [1,2], predicts the average behavior of the bunching
probability and is known as the bosonic birthday paradox. The second rule is
new, and establishes a n!-factor quantum enhancement for the probability that
all n bosons bunch in a single output mode, with respect to the case of
distinguishable bosons. Besides its fundamental importance in phenomena such as
Bose-Einstein condensation, bosonic bunching can be exploited in applications
such as linear optical quantum computing and quantum-enhanced metrology.Comment: 6 pages, 4 figures, and supplementary material (4 pages, 1 figure
Cryptographically Secure Information Flow Control on Key-Value Stores
We present Clio, an information flow control (IFC) system that transparently
incorporates cryptography to enforce confidentiality and integrity policies on
untrusted storage. Clio insulates developers from explicitly manipulating keys
and cryptographic primitives by leveraging the policy language of the IFC
system to automatically use the appropriate keys and correct cryptographic
operations. We prove that Clio is secure with a novel proof technique that is
based on a proof style from cryptography together with standard programming
languages results. We present a prototype Clio implementation and a case study
that demonstrates Clio's practicality.Comment: Full version of conference paper appearing in CCS 201
Evaluation of two interaction techniques for visualization of dynamic graphs
Several techniques for visualization of dynamic graphs are based on different
spatial arrangements of a temporal sequence of node-link diagrams. Many studies
in the literature have investigated the importance of maintaining the user's
mental map across this temporal sequence, but usually each layout is considered
as a static graph drawing and the effect of user interaction is disregarded. We
conducted a task-based controlled experiment to assess the effectiveness of two
basic interaction techniques: the adjustment of the layout stability and the
highlighting of adjacent nodes and edges. We found that generally both
interaction techniques increase accuracy, sometimes at the cost of longer
completion times, and that the highlighting outclasses the stability adjustment
for many tasks except the most complex ones.Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
Hang With Your Buddies to Resist Intersection Attacks
Some anonymity schemes might in principle protect users from pervasive
network surveillance - but only if all messages are independent and unlinkable.
Users in practice often need pseudonymity - sending messages intentionally
linkable to each other but not to the sender - but pseudonymity in dynamic
networks exposes users to intersection attacks. We present Buddies, the first
systematic design for intersection attack resistance in practical anonymity
systems. Buddies groups users dynamically into buddy sets, controlling message
transmission to make buddies within a set behaviorally indistinguishable under
traffic analysis. To manage the inevitable tradeoffs between anonymity
guarantees and communication responsiveness, Buddies enables users to select
independent attack mitigation policies for each pseudonym. Using trace-based
simulations and a working prototype, we find that Buddies can guarantee
non-trivial anonymity set sizes in realistic chat/microblogging scenarios, for
both short-lived and long-lived pseudonyms.Comment: 15 pages, 8 figure
Walking dynamics are symmetric (enough)
Many biological phenomena such as locomotion, circadian cycles, and breathing
are rhythmic in nature and can be modeled as rhythmic dynamical systems.
Dynamical systems modeling often involves neglecting certain characteristics of
a physical system as a modeling convenience. For example, human locomotion is
frequently treated as symmetric about the sagittal plane. In this work, we test
this assumption by examining human walking dynamics around the steady-state
(limit-cycle). Here we adapt statistical cross validation in order to examine
whether there are statistically significant asymmetries, and even if so, test
the consequences of assuming bilateral symmetry anyway. Indeed, we identify
significant asymmetries in the dynamics of human walking, but nevertheless show
that ignoring these asymmetries results in a more consistent and predictive
model. In general, neglecting evident characteristics of a system can be more
than a modeling convenience---it can produce a better model.Comment: Draft submitted to Journal of the Royal Society Interfac
Steps Towards a Method for the Formal Modeling of Dynamic Objects
Fragments of a method to formally specify object-oriented models of a universe of discourse are presented. The task of finding such models is divided into three subtasks, object classification, event specification, and the specification of the life cycle of an object. Each of these subtasks is further subdivided, and for each of the subtasks heuristics are given that can aid the analyst in deciding how to represent a particular aspect of the real world. The main sources of inspiration are Jackson System Development, algebraic specification of data- and object types, and algebraic specification of processes
Geometric Universality of Currents
We discuss a non-equilibrium statistical system on a graph or network.
Identical particles are injected, interact with each other, traverse, and leave
the graph in a stochastic manner described in terms of Poisson rates, possibly
dependent on time and instantaneous occupation numbers at the nodes of the
graph. We show that under the assumption of constancy of the relative rates,
the system demonstrates a profound statistical symmetry, resulting in geometric
universality of the statistics of the particle currents. This phenomenon
applies broadly to many man-made and natural open stochastic systems, such as
queuing of packages over the internet, transport of electrons and
quasi-particles in mesoscopic systems, and chains of reactions in bio-chemical
networks. We illustrate the utility of our general approach using two enabling
examples from the two latter disciplines.Comment: 15 pages, 5 figure
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