146 research outputs found
No Need to Know Physics: Resilience of Process-based Model-free Anomaly Detection for Industrial Control Systems
In recent years, a number of process-based anomaly detection schemes for
Industrial Control Systems were proposed. In this work, we provide the first
systematic analysis of such schemes, and introduce a taxonomy of properties
that are verified by those detection systems. We then present a novel general
framework to generate adversarial spoofing signals that violate physical
properties of the system, and use the framework to analyze four anomaly
detectors published at top security conferences. We find that three of those
detectors are susceptible to a number of adversarial manipulations (e.g.,
spoofing with precomputed patterns), which we call Synthetic Sensor Spoofing
and one is resilient against our attacks. We investigate the root of its
resilience and demonstrate that it comes from the properties that we
introduced. Our attacks reduce the Recall (True Positive Rate) of the attacked
schemes making them not able to correctly detect anomalies. Thus, the
vulnerabilities we discovered in the anomaly detectors show that (despite an
original good detection performance), those detectors are not able to reliably
learn physical properties of the system. Even attacks that prior work was
expected to be resilient against (based on verified properties) were found to
be successful. We argue that our findings demonstrate the need for both more
complete attacks in datasets, and more critical analysis of process-based
anomaly detectors. We plan to release our implementation as open-source,
together with an extension of two public datasets with a set of Synthetic
Sensor Spoofing attacks as generated by our framework
Efficient Calculation of Derivatives of Integrals in a Basis of Non-Separable Gaussians Through Exploitation of Sparsity
A computational procedure is developed for the efficient calculation of
derivatives of integrals over non-separable Gaussian-type basis functions, used
for the evaluation of gradients of the total energy in quantum-mechanical
simulations. The approach, based on symbolic computation with computer algebra
systems and automated generation of optimized subroutines, takes full advantage
of sparsity and is here applied to first energy derivatives with respect to
nuclear displacements and lattice parameters of molecules and materials. The
implementation in the \textsc{Crystal} code is presented and the considerably
improved computational efficiency over the previous implementation is
illustrated. To this purpose, three different tasks involving the use of
analytical forces are considered: i) geometry optimization; ii) harmonic
frequency calculation; iii) elastic tensor calculation. Three test case
materials are selected as representatives of different classes: i) a metallic
2D model of the Cu (111) surface; ii) a wide-gap semiconductor ZnO crystal,
with a wurtzite-type structure; and iii) a porous metal-organic crystal, namely
the ZIF-8 Zinc-imidazolate framework. Finally, it is argued that the present
symbolic approach is particularly amenable to generalizations, and its
potential application to other derivatives is sketched
Anharmonic Terms of the Potential Energy Surface: A Group Theoretical Approach
In the framework of density functional theory (DFT) simulations of molecules
and materials, anharmonic terms of the potential energy surface are commonly
computed numerically, with an associated cost that rapidly increases with the
size of the system. Recently, an efficient approach to calculate cubic and
quartic interatomic force constants in the basis of normal modes [Theor. Chem.
Acc., 120, 23 (2008)] was implemented in the Crystal program [J. Chem. Theory
Comput., 15, 3755-3765 (2019)]. By applying group theory, we are able to
further reduce the associated computational cost, as the exploitation of point
symmetry can significantly reduce the number of distinct atomically displaced
nuclear configurations to be explicitly explored for energy and forces
calculations. Our strategy stems from Wigner's theorem and the fact that normal
modes are bases of the irreducible representations (irreps) of the point group.
The proposed group theoretical approach is implemented in the Crystal program
and its efficiency assessed on six test case systems: four molecules (methane,
CH4; tetrahedrane, C4H4; cyclo-exasulfur, S6; cubane, C8H8), and two
three-dimensional crystals (Magnesium oxide, MgO; and a prototypical
Zinc-imidazolate framework, ZIF-8). The speedup imparted by this approach is
consistently very large in all high-symmetry molecular and periodic systems,
peaking at 76% for MgO
Structural Relaxation of Materials with Spin-Orbit Coupling: Analytical Forces in Spin-Current DFT
Analytical gradients of the total energy are provided for local density and
generalized-gradient hybrid approximations to generalized Kohn-Sham
spin-current density functional theory (SCDFT). It is shown that gradients may
be determined analytically, in a two-component framework, including spin-orbit
coupling (SOC), with high accuracy. We demonstrate that renormalization of the
electron-electron potential by SOC-induced spin-currents can account for
considerable modification of crystal structures. In the case of Iodine-based
molecular crystals, the effect may amount to more than half of the total
modification of the structure by SOC. Such effects necessitate an SCDFT, rather
than DFT, formulation, in which exchange-correlation functionals are endowed
with an explicit dependence on spin-current densities. An implementation is
presented in the \textsc{Crystal} program
Measurement incompatibility is strictly stronger than disturbance
The core of Heisenberg's argument for the uncertainty principle, involving
the famous -ray microscope , consists in
the existence of measurements that irreversibly alter the state of the system
on which they are acting, causing an irreducible disturbance on subsequent
measurements. The argument was put forward to justify the existence of
incompatible measurements, namely, measurements that cannot be performed
jointly. In this Letter, on the one hand, we provide a compelling argument
showing that incompatibility is indeed a sufficient condition for disturbance,
while, on the other hand, we exhibit a toy theory that is a counterexample for
the converse implication.Comment: 21 pages (5 main text + 16 supplemental material); no figures, lots
of diagram
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