Alexander A. Semenov

Estimation of Normalized Atmospheric Point Spread Function and Restoration of Remotely Sensed Images

The Earths atmosphere heavily affects the remote sensing images collected by spaceborne passive optical sensors due to radiation-matter interaction phenomena like radiation absorption, scattering, and thermal emission. A complex phenomenon is the adjacency effect, i.e., radiation reflected by the ground that, due to the atmospheric scattering, is being seen in a viewing direction different from that corresponding to the ground location that reflected it. Adjacency gives rise to crosstalk between neighboring picture elements up to a distance that depends on the width of the integral kernel function employed for the mathematical modeling of the problem. As long as the atmosphere is a linear space-invariant system, the adjacency can be modeled as a low-pass filter, with the atmospheric point spread function (APSF) applied to the initial image. In this paper, a direct method of estimating the discrete normalized APSF (NAPSF) using images gathered by high-resolution optical sensors is discussed. We discuss the use of the NAPSF estimate for deducing the Correction Spatial high-pass Filter (CSF)-a correction filter that removes the adjacency effect. The NAPSF estimation procedure has been investigated using statistical simulations, whose outcomes permitted us to identify the conditions under which the NAPSF could be measured with acceptable errors. The NAPSF estimation is examined for various natural images acquired by MOMS-2P, CHRIS, AVIRIS, and MIVIS.

Parallel logical cryptanalysis of the generator A5/1 in BNB-grid system

In logical cryptanalysis a problem of search of a secret key of a cryptographic system is formulated as a SAT problem, i.e. a problem of search of a satisfying assignment for some CNF. In this paper we consider some natural strategies for parallelization of these SAT problems. We apply coarse-grained approach which makes it possible to use distributed computing environments with slow interconnect. The main practical result of this paper is successful logical cryptanalysis of keystream generator A5/1 in BNB-Grid system.

Using Monte Carlo Method for Searching Partitionings of Hard Variants of Boolean Satisfiability Problem

In this paper we propose the approach for constructing partitionings of hard variants of the Boolean satisfiability problem SAT. Such partitionings can be used for solving corresponding SAT instances in parallel. We suggest the approach based on the Monte Carlo method for estimating time of processing of an arbitrary partitioning. We solve the problem of search for a partitioning with good effectiveness via the optimization of the special predictive function over the finite search space. For this purpose we use the tabu search strategy. In our computational experiments we found partitionings for SAT instances encoding problems of inversion of some cryptographic functions. Several of these SAT instances with realistic predicted solving time were successfully solved on a computing cluster and in the volunteer computing project [emailxa0protected] The solving time agrees well with estimations obtained by the proposed method.

SAT-based search for systems of diagonal latin squares in volunteer computing project SAT@home

In this paper we considered the problem of finding pairs of mutually orthogonal diagonal Latin squares of order 10. First we reduced it to Boolean satisfiability problem. The obtained instance is very hard, therefore we decomposed it into a family of subproblems. To solve the latter we used the volunteer computing project SAT@home. In the course of 10-month long computational experiment we managed to find 29 pairs of described kind, that are different from already known pairs. Also we considered the problem of search for triples of diagonal Latin squares of order 10 that satisfy weakened orthogonality condition. Using diagonal Latin squares from the known pairs (the most of them were found in SAT@home) we constructed new triples of proposed kind. During this computational experiment we used a computing cluster.

The application of parameterized algorithms for solving SAT to the study of several discrete models of collective behavior

In this paper we present the computational study of one class of discrete models of collective behavior. In the context of these models a set of agents, that form a collective, is represented by a network. Each agent is assigned a special weight function. The behavior of a collective in discrete time moments is specified with a vector function, the coordinates of which are defined by values of agents weight functions at corresponding time moments. We study phenomena concerning the so-called conforming behavior: when an agent at some time moment decides to act or not to act depending on the similar decisions, made by agents from its neighborhood at the previous moment. We consider the problem how to dispose a relatively small number of always acting agents called activators in the network so that the majority of agents soon become active. We apply state-of-the-art SAT solvers to this problem. To tune the solver we use special parameterization techniques. In our computational experiments we show that the solving of considered problems of large dimension can be significantly sped up by finding effective combinations of the SAT solver parameters values on test instances from the same class but of much lower dimension.

A Volunteer-Computing-Based Grid Architecture Incorporating Idle Resources of Computational Clusters.

In this paper, we suggest a new architecture of a computational grid that involves resources of BOINC-based volunteer computing projects and idle resources of computational clusters. We constructed a computational grid of the proposed kind, based on several computational clusters and the volunteer computing project SAT@home. This project, launched and maintained by us, is aimed at solving hard computational problems, which can be effectively reduced to Boolean satisfiability problem. In the constructed grid several new combinatorial designs based on diagonal Latin squares of order 10 were found, and also several weakened cryptanalysis problems for the Bivium cipher were solved.

Improving the effectiveness of SAT approach in application to analysis of several discrete models of collective behavior

In this paper we study several discrete models of collective behavior based on Synchronous Boolean Networks. For these models we consider a number of related problems that we solve by reducing them to Boolean satisfiability problem (SAT) and applying state-of-the-art parameterized SAT solving algorithms. We describe a greedy algorithm that exploits the features of functions used to recalculate network nodes weights and interconnections between neighborhoods of network nodes. This algorithm in combination with several specific propositional encoding techniques, makes it possible to significantly reduce the size of propositional encoding. We compare the effectiveness of SAT solving algorithms on the new encodings with that on previously employed encodings and evaluate the total performance gain achieved by using state-of-the-art tools for finding efficient SAT solver parameters.

Concept of a multitask grid system with a flexible allocation of idle computational resources of supercomputers

A new concept of a multitask distributed heterogeneous computing system is proposed. The basic principles of such system are that it uses only idle supercomputer resources and does it as a common user; thus, it does not conflict with the administration policy in any way. The efficiency of the proposed concept is demonstrated by the example of the real grid system that currently uses supercomputer resources to boost the performance of the SAT@home and OPTIMA@home volunteer distributed computing projects.

Using automatic generation of relaxation constraints to improve the preimage attack on 39-step MD4

In this paper we construct preimage attack on the truncated variant of the MD4 hash function. Specifically, we study the MD4-39 function defined by the first 39 steps of the MD4 algorithm. We suggest a new attack on MD4-39, which develops the ideas proposed by H. Dobbertin in 1998. Namely, the special relaxation constraints are introduced in order to simplify the equations corresponding to the problem of finding a preimage for an arbitrary MD4-39 hash value. The equations supplemented with the relaxation constraints are then reduced to the Boolean Satisfiability Problem (SAT) and solved using the state-of-the-art SAT solvers. We show that the effectiveness of a set of relaxation constraints can be evaluated using the black-box function of a special kind. Thus, we suggest automatic method of relaxation constraints generation by applying the black-box optimization to this function. The proposed method made it possible to find new relaxation constraints that contribute to a SAT-based preimage attack on MD4-39 which significantly outperforms the competition.

Runtime estimation for enumerating all mutually orthogonal diagonal Latin squares of order 10

In the present paper we estimate how long it will take state-of-the-art combinatorial algorithms to enumerate all possible mutually orthogonal diagonal Latin squares of order 10. For this purpose we first evaluate the performance of DLX algorithm and contemporary algorithms for solving SAT in application to finding orthogonal mates of an arbitrary diagonal Latin square of order 10. Then we estimate the number of diagonal Latin squares of order 10 and use this information in combination with some techniques for exploiting symmetries and equivalences to approximate the amount of time it would take to process them using existing hardware.