804 research outputs found
Relational reasoning via probabilistic coupling
Probabilistic coupling is a powerful tool for analyzing pairs of
probabilistic processes. Roughly, coupling two processes requires finding an
appropriate witness process that models both processes in the same probability
space. Couplings are powerful tools proving properties about the relation
between two processes, include reasoning about convergence of distributions and
stochastic dominance---a probabilistic version of a monotonicity property.
While the mathematical definition of coupling looks rather complex and
cumbersome to manipulate, we show that the relational program logic pRHL---the
logic underlying the EasyCrypt cryptographic proof assistant---already
internalizes a generalization of probabilistic coupling. With this insight,
constructing couplings is no harder than constructing logical proofs. We
demonstrate how to express and verify classic examples of couplings in pRHL,
and we mechanically verify several couplings in EasyCrypt
Tracking Data-Flow with Open Closure Types
Type systems hide data that is captured by function closures in function
types. In most cases this is a beneficial design that favors simplicity and
compositionality. However, some applications require explicit information about
the data that is captured in closures. This paper introduces open closure
types, that is, function types that are decorated with type contexts. They are
used to track data-flow from the environment into the function closure. A
simply-typed lambda calculus is used to study the properties of the type theory
of open closure types. A distinctive feature of this type theory is that an
open closure type of a function can vary in different type contexts. To present
an application of the type theory, it is shown that a type derivation
establishes a simple non-interference property in the sense of information-flow
theory. A publicly available prototype implementation of the system can be used
to experiment with type derivations for example programs.Comment: Logic for Programming Artificial Intelligence and Reasoning (2013
Computational Soundness for Dalvik Bytecode
Automatically analyzing information flow within Android applications that
rely on cryptographic operations with their computational security guarantees
imposes formidable challenges that existing approaches for understanding an
app's behavior struggle to meet. These approaches do not distinguish
cryptographic and non-cryptographic operations, and hence do not account for
cryptographic protections: f(m) is considered sensitive for a sensitive message
m irrespective of potential secrecy properties offered by a cryptographic
operation f. These approaches consequently provide a safe approximation of the
app's behavior, but they mistakenly classify a large fraction of apps as
potentially insecure and consequently yield overly pessimistic results.
In this paper, we show how cryptographic operations can be faithfully
included into existing approaches for automated app analysis. To this end, we
first show how cryptographic operations can be expressed as symbolic
abstractions within the comprehensive Dalvik bytecode language. These
abstractions are accessible to automated analysis, and they can be conveniently
added to existing app analysis tools using minor changes in their semantics.
Second, we show that our abstractions are faithful by providing the first
computational soundness result for Dalvik bytecode, i.e., the absence of
attacks against our symbolically abstracted program entails the absence of any
attacks against a suitable cryptographic program realization. We cast our
computational soundness result in the CoSP framework, which makes the result
modular and composable.Comment: Technical report for the ACM CCS 2016 conference pape
Machine Assisted Proof of ARMv7 Instruction Level Isolation Properties
In this paper, we formally verify security properties of the ARMv7 Instruction Set Architecture (ISA) for user mode executions.
To obtain guarantees that arbitrary (and unknown) user processes are able to run isolated from privileged software and other user processes, instruction level noninterference and integrity properties are provided, along with proofs that transitions to privileged modes can only occur in a controlled manner.
This work establishes a main requirement for operating system and hypervisor verification, as demonstrated for the PROSPER separation kernel. The proof is performed in the HOL4 theorem prover, taking the Cambridge model of ARM as basis.
To this end, a proof tool has been developed, which assists the verification of relational state predicates semi-automatically
Sulfadimethoxine residues in rabbit muscle after extended oral treatment at therapeutic dosage
[EN] Sulfadimethoxine is extensively used in rabbit breeding for preventive and curative purpose and residues are sometimes observed in carcasses at slaughter. It has been suggested this is due to dosage and/or duration of treatment not being in compliance with the manufacturer's recommendations, which probably induces residue levels in the meat above the maximum residue limit (MRL) value of 100 Âżg/kg. In order to test this hypothesis, a study was carried out on gravid rabbits and their progeny. The animals were subjected to an extended treatment with sulfadimethoxine at therapeutic level in the feed. The feed was supplemented before pelleting with a commercial veterinary product containing 20 g of trimethoprim and 93 g of sulfadimethoxine per kg. On the basis of the dosage indicated for this commercial veterinary product, the incorporation level in the feed was 5 kg/ton (i.e. 465 g of sulfadimethoxine/ton), providing oral daily therapeutic treatment of the animals of ca. 12.5 to 50 mg of sulfadimethoxine per kg bodyweight. The mothers were treated during the last 21 d of pregnancy and during the whole period of lactation (35 d). The animals were sacrificed after a wash-out period of 12 d with blank feed. The young rabbits received the supplemented feed after weaning during the first 40 d of the fattening period. These animals were also sacrifi ced after a wash-out period of 8, 12, 15 or 20 d, respectively, with a blank feed. A sample of the leg muscle was taken for analysis. An HPLC analytical method was used to determine the sulfadimethoxine concentrations in tissue, with a LLOQ (Lower Limit Of Quantification) of 50 Âżg/kg of muscle (trimethoprim was not considered in this study). Sulfadimethoxine concentrations above the MRL value of 100 Âżg/kg were registered only in muscle from 1 out of 8 mothers and in 2 out of 8 young rabbits sacrificed 12 d after cessation of the treatment. For other young rabbits sacrificed on the 8th, 15th or 20th d after cessation of treatment, Sulphonamide concentrations in muscle always remained below the MRL value (8 animals per slaughtering time). These results show that oral treatment of rabbits with veterinary products containing sulfadimethoxine administered for a long period at the daily therapeutic level of 12.5 to 50 mg/kg does not seem to induce the accumulation of this molecule in muscle.Barthe, C.; Guicherd, A.; Quillon, J. (2009). Sulfadimethoxine residues in rabbit muscle after extended oral treatment at therapeutic dosage. World Rabbit Science. 17(3):137-144. doi:10.4995/wrs.2009.65313714417
Metallicity determination in gas-rich galaxies with semiempirical methods
A study of the precision of the semiempirical methods used in the
determination of the chemical abundances in gas-rich galaxies is carried out.
In order to do this the oxygen abundances of a total of 438 galaxies were
determined using the electronic temperature, the and the P methods.
The new calibration of the P method gives the smaller dispersion for the low
and high metallicity regions, while the best numbers in the turnaround region
are given by the method. We also found that the dispersion correlates
with the metallicity. Finally, it can be said that all the semiempirical
methods studied here are quite insensitive to metallicity with a value of
dex for more than 50% of the total sample.
\keywords{ISM: abundances; (ISM): H {\sc ii} regions}Comment: 26 pages, 9 figures and 2 tables. To appear at AJ, January 200
Geometric inequalities from phase space translations
We establish a quantum version of the classical isoperimetric inequality
relating the Fisher information and the entropy power of a quantum state. The
key tool is a Fisher information inequality for a state which results from a
certain convolution operation: the latter maps a classical probability
distribution on phase space and a quantum state to a quantum state. We show
that this inequality also gives rise to several related inequalities whose
counterparts are well-known in the classical setting: in particular, it implies
an entropy power inequality for the mentioned convolution operation as well as
the isoperimetric inequality, and establishes concavity of the entropy power
along trajectories of the quantum heat diffusion semigroup. As an application,
we derive a Log-Sobolev inequality for the quantum Ornstein-Uhlenbeck
semigroup, and argue that it implies fast convergence towards the fixed point
for a large class of initial states.Comment: 37 pages; updated to match published versio
In-flight calibration of the Hot Ion Analyser on board Cluster
The Hot Ion Analyser (HIA), part of the Cluster Ion Spectrometry experiment,
has the objective to measure the three-dimensional velocity distributions of
ions. Due to a variety of factors (exposure to radiation, detector fatigue
and aging, changes in the operating parameters, etc.), the particles' detection
efficiency changes over time, prompting for continuous in-flight calibration.
This is achieved by comparing the HIA data with the data provided by the
WHISPER (Waves of HIgh frequency and Sounder for Probing of Electron
density by Relaxation) experiment on magnetosheath intervals, for the high-sensitivity
section of the instrument, or solar wind intervals, for the low-sensitivity
section. The paper presents in detail the in-flight calibration methodology,
reports on the work carried out for calibrating HIA and discusses plans to
extend this activity in order to ensure the instrument's highest data accuracy
Isoperimetry and stability of hyperplanes for product probability measures
International audienceWe investigate stationarity and stability of half-spaces as isoperimetric sets for product probability measures, considering the cases of coordinate and non-coordinate half-spaces. Moreover, we present several examples to which our results can be applied, with a particular emphasis on the logistic measure
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