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linear-approximations
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Fast correlation attacks on the summation generator
, Article Journal of Cryptology ; Volume 13, Issue 2 , 2000 , Pages 245-262 ; 09332790 (ISSN) ; Salmasizadeh, M ; Dawson, E ; Sharif University of Technology
Springer New York
2000
Abstract
Abstract. The linear sequential circuit approximation method for combiners with memory is used to find mutually correlated linear transforms of the input and output sequences in the well-known summation generator with any number of inputs. It is shown that the determined correlation coefficient is large enough for applying a fast correlation attack to the output sequence to reconstruct the initial states of the input linear feedback shift registers. The proposed attack is based on iterative probabilistic decoding and appropriately generated low-weight parity-checks. The required output sequence length and the computational complexity are both derived. Successful experimental results for the...
Piece-wise Linear Approximation of Step Response for GSI Interconnects
, M.Sc. Thesis Sharif University of Technology ; Sarvari, Reza (Supervisor)
Abstract
Since interconnects are playing a very important role in today’s IC technology, introducing new models and approximations is vital to IC designers. In this dissertation, maxwell equations are introduced as they are the main equations governing transmission lines. Different methods to model interconnects are also presented. Moreover, because of the importance of the step response of a system, available methods for finding the step response of interconnects are briefly discussed. Some approximations are also described, which result in faster but not very accurate responses. Delay and noise in integrated circuit connections have been the subject of several investigations for a long time. Since...
Cryptanalysis of Stream Ciphers By Structural Attacks
, M.Sc. Thesis Sharif University of Technology ; Aref, Mohammad Reza (Supervisor) ; Mohajeri, Javad (Supervisor)
Abstract
According to the development of communication, cryptography has become a vital issue. Several algorithms have been introduced for cryptography applications. Stream ciphers are such algorithms with high speed and appropriate efficiency. Lots of attacks have been applied to stream ciphers. We concentrate on two kinds of attacks in this thesis. Distinguishing attack is a general attack in which the attacker tries to distinguish the observed output sequence from random. Designers apply this kind of attack to test the statistical probabilities of the output sequence. We applied this attack on Grain family and Trivium family. In the proposed attack, nonlinear parts are replaced with linear ones....
Distinguishing attack on bivium
, Article Proceedings - 10th IEEE International Conference on Computer and Information Technology, CIT-2010, 7th IEEE International Conference on Embedded Software and Systems, ICESS-2010, ScalCom-2010, 29 June 2010 through 1 July 2010, Bradford ; 2010 , Pages 1075-1078 ; 9780769541082 (ISBN) ; Rohani, N ; Mohajeri, J ; Aref, M. R ; Sharif University of Technology
2010
Abstract
Bivium is a simplified version of Trivium, a hardware profile finalist of eSTREAM project. Bivium has an internal state of size 177 bits and a key length of 80 bits. In this paper we introduce a distinguishing attack on this cipher. In this method we first find the best linear approximation for the updating function. Then by using this approximation, and optimizing the time delay, we find the distinguisher. The complexity of the attack is O(230.79), which is an improvement to the previous distinguishing attack with a complexity of order O(232)
Efficient method for simplifying and approximating the S-boxes based on power functions
, Article IET Information Security ; Volume 3, Issue 3 , 2009 , Pages 114-118 ; 17518709 (ISSN) ; Aref, M. R ; Sharif University of Technology
2009
Abstract
In recently proposed cipher algorithms, power functions over finite fields and specially inversion functions play an important role in the S-box design structure. In this study, a new systematic efficient method is introduced to cryptanalyse (to simplify and approximate) such S-boxes. This method is very simple and does not need any heuristic attempt and can be considered as a quick criterion to find some simple approximations. Using this new method, some approximations can be obtained for advanced encryption standard (AES) like S-boxes, such as AES, Camellia, Shark and so on. Finally as an application of this method, a simple linear approximation for AES S-box is presented. © The...
Piecewise-linear approximations of uncertain functions
, Article 12th International Symposium on Algorithms and Data Structures, WADS 2011, New York, NY, 15 August 2011 through 17 August 2011 ; Volume 6844 LNCS , 2011 , Pages 1-12 ; 03029743 (ISSN) ; 9783642222993 (ISBN) ; De Berg, M ; Khosravi, A ; Sharif University of Technology
Abstract
We study the problem of approximating a function F:ℝ → ℝ by a piecewise-linear function F̄ when the values of F at {x 1,...,xn} are given by a discrete probability distribution. Thus, for each xi we are given a discrete set y i,1,..., yi,mi of possible function values with associated probabilities pi,j such that Pr[F(xi) = yi,j] = pi,j. We define the error of F̄ as error(F, F̄) = maxi=1n E[|Fxi) - F̄(xi)|]. Let m = ∑i=1nmi be the total number of potential values over all F(xi). We obtain the following two results: (i) an O(m) algorithm that, given F and a maximum error ε, computes a function F̄ with the minimum number of links such that error(F, F̄) ≤ ε; (ii) an O(n4/3+δ + mlogn) algorithm...
A competitive inexact nonmonotone filter SQP method: convergence analysis and numerical results
, Article Optimization Methods and Software ; 2021 ; 10556788 (ISSN) ; Mahdavi Amiri, N ; Sharif University of Technology
Taylor and Francis Ltd
2021
Abstract
We propose an inexact nonmonotone successive quadratic programming (SQP) algorithm for solving nonlinear programming problems with equality constraints and bounded variables. Regarding the value of the current feasibility violation and the minimum value of its linear approximation over a trust region, several scenarios are envisaged. In one scenario, a possible infeasible stationary point is detected. In other scenarios, the search direction is computed using an inexact (truncated) solution of a feasible strictly convex quadratic program (QP). The search direction is shown to be a descent direction for the objective function or the feasibility violation in the feasible or infeasible...
A competitive inexact nonmonotone filter SQP method: convergence analysis and numerical results
, Article Optimization Methods and Software ; 2021 ; 10556788 (ISSN) ; Mahdavi Amiri, N ; Sharif University of Technology
Taylor and Francis Ltd
2021
Abstract
We propose an inexact nonmonotone successive quadratic programming (SQP) algorithm for solving nonlinear programming problems with equality constraints and bounded variables. Regarding the value of the current feasibility violation and the minimum value of its linear approximation over a trust region, several scenarios are envisaged. In one scenario, a possible infeasible stationary point is detected. In other scenarios, the search direction is computed using an inexact (truncated) solution of a feasible strictly convex quadratic program (QP). The search direction is shown to be a descent direction for the objective function or the feasibility violation in the feasible or infeasible...
Designing Hybrid Controller, Impleimentation on Experiment Model and Proving Stability for 3-Pole AMB
, M.Sc. Thesis Sharif University of Technology ; Salarieh, Hassan (Supervisor) ; Alasti, Aria (Supervisor)
Abstract
The design and implementation of the hybrid control method for a three-pole active magnetic bearing (AMB) is proposed in this paper. The system is inherently nonlinear and conventional nonlinear controllers are a little complicated while the proposed hybrid controller has a piecewise linear form, i.e., linear in each sub-region. A state-feedback hybrid controller is designed in this study and the unmeasurable states are estimated by an observer. The gains of the hybrid controller are obtained by the LQR method in each sub-region. To evaluate the performance, the designed controller is implemented on an experimental setup. The experimental results show that the proposed method can efficiently...
Neutron noise simulation by GFEM and unstructured triangle elements
, Article Nuclear Engineering and Design ; Volume 253 , 2012 , Pages 238-258 ; 00295493 (ISSN) ; Vosoughi, N ; Sharif University of Technology
2012
Abstract
In the present study, the neutron noise, i.e. The stationary fluctuation of the neutron flux around its mean value, is calculated in 2-group forward and adjoint diffusion theory for both hexagonal and rectangular reactor cores. To this end, the static neutron calculation is performed at the first stage. The spatial discretization of equations is based on linear approximation of Galerkin Finite Element Method (GFEM) using unstructured triangle elements. Using power iteration method, forward and adjoint fluxes with the corresponding eigenvalues are obtained. The results are then benchmarked against the valid results for BIBLIS-2D and IAEA-2D benchmark problems and DONJON computer code. The...
Target direct position determination in 2D CW forward scatter radar
, Article Proceedings International Radar Symposium, 10 May 2016 through 12 May 2016 ; Volume 2016-June , 2016 ; 21555753 (ISSN) ; 9781509025183 (ISBN) ; Adelipour, S ; Behnia, F ; Nayebi, M. M ; Sharif University of Technology
IEEE Computer Society
2016
Abstract
This paper proposes an algebraic solution for the position and velocity of a moving target in forward scatter radar based on a single step direct position determination method. Unlike the conventional two-step method, this direct technique does not require the joint estimation of the Doppler frequency and the angle of arrival, initialization step, convergence considerations and linearization approximations
State waypoint approach to continuous-time nonlinear optimal control problems
, Article Asian Journal of Control ; Volume 11, Issue 6 , 2009 , Pages 669-676 ; 15618625 (ISSN) ; Tazaki, Y ; Imura, J. I ; Sharif University of Technology
2009
Abstract
In this paper, we propose an optimal control technique for a class of continuous-time nonlinear systems. The key idea of the proposed approach is to parametrize continuous stale trajectories by sequences of a finite number of intermediate target states; namely, waypoint sequences. It is shown that the optimal control problem for transferring the state from one waypoint to the next is given an explicit-form suboptimal solution, by means of linear approximation. Thus the original continuous-time nonlinear control problem reduces to a finite-dimensional optimization problem of waypoint sequences. Any efficient numerical optimization method, such as the interior-reflection Newton method, can be...
Autoregressive video modeling through 2D Wavelet Statistics
, Article Proceedings - 2010 6th International Conference on Intelligent Information Hiding and Multimedia Signal Processing, IIHMSP 2010, 15 October 2010 through 17 October 2010 ; October , 2010 , Pages 272-275 ; 9780769542225 (ISBN) ; Ghaemmaghami, S ; Shirmohammadi, S ; Sharif University of Technology
2010
Abstract
We present an Autoregressive (AR) modeling method for video signal analysis based on 2D Wavelet Statistics. The video signal is assumed to be a combination of spatial feature time series that are temporally approximated by the AR model. The AR model yields a linear approximation to the temporal evolution of a stationary stochastic process. Generalized Gaussian Density (GGD) parameters, extracted from 2D wavelet transform subbands, are used as the spatial features. Wavelet transform efficiently resembles the Human Visual System (HVS) characteristics and captures more suitable features, as compared to color histogram features. The AR model describes each spatial feature vector as a linear...
Modeling of the boost power factor correction rectifier in mixed conduction mode using PWA approximation
, Article 2008 IEEE International Symposium on Industrial Electronics, ISIE 2008, Cambridge, 30 June 2008 through 2 July 2008 ; 2008 , Pages 190-195 ; 1424416655 (ISBN); 9781424416653 (ISBN) ; Gholami, B ; Ahmadian, H. M ; Sharif University of Technology
2008
Abstract
PFC converters for higher power are commonly designed for continuous conduction mode (CCM). However, at light load, discontinuous conduction mode (DCM) will appear close to the crossover of the line voltage, causing the converter to switch between the two conduction modes. As a result, the converter dynamics change abruptly, producing input current distortion. In this article a piecewise affine approximation has been employed in modeling a boost power factor correction converter operated in the mixed conduction mode. This approach makes the new model very useful in large signal analysis of PFC rectifiers and design of controller. The results obtained from the proposed model are compared with...