scholarly journals Improved Preimage Attacks on 3-Round Keccak-224/256

2021 ◽  
pp. 84-101
Author(s):  
Xiaoen Lin ◽  
Le He ◽  
Hongbo Yu
Keyword(s):  
Degrees Of Freedom ◽  
Linear Structure ◽  
Improved Method ◽  
Two Stages

In this paper, we provide an improved method on preimage attacks of standard 3-round Keccak-224/256. Our method is based on the work by Li and Sun. Their strategy is to find a 2-block preimage instead of a 1-block one by constructing the first and second message blocks in two stages. Under this strategy, they design a new linear structure for 2-round Keccak-224/256 with 194 degrees of freedom left, which is able to construct the second message block with a complexity of 231/262. However, the bottleneck of this strategy is that the first stage needs much more expense than the second one. Therefore, we improve the first stage by using two techniques. The first technique is constructing multi-block messages rather than one-block message in the first stage, which can reach a better inner state. The second technique is setting restricting equations more efficiently, which can work in 3-round Keccak-256. As a result, the complexity of finding a preimage for 3-round Keccak-224/256 can be decreased from 238/281 to 232/265.

An Improved Method for Calculating Free Vibrations in Systems of Several Degrees of Freedom

1938 ◽  
Vol 5 (2) ◽  
pp. A61-A66
Author(s):  
Winston M. Dudley
Keyword(s):  
Degrees Of Freedom ◽  
Numerical Solutions ◽  
Matrix Theory ◽  
Free Vibrations ◽  
Initial Disturbance ◽  
Improved Method ◽  
Matrix Methods ◽  
Computing Machine ◽  
The Matrix ◽  
Time Required

Abstract In 1934 two English investigators (1) published a method for calculating the various modes and frequencies of vibration of a system having several degrees of freedom. Their method, which is based on matrices, greatly shortens the time spent in obtaining numerical solutions in many important problems, notably those with immovable foundations. In this paper is presented a new theorem which (a) makes possible a further reduction of nearly one half in the time required, so that solutions up to 20 deg or more of freedom are now practical and (b) makes it then possible to determine the motion of the system after any initial disturbance in a few minutes, instead of several hours as required by older methods. It is useful in the latter respect whether the modes have been determined by matrix methods, or not. Although the paper gives simpler proofs than any previously published, knowledge of the matrix theory is not required in using the method. Problems are analyzed by a tabular process, in which an ordinary computing machine helps greatly. Comments based on computing experience are given. A simple numerical example has been given elsewhere (1).

An Improved Multi-Label Classifier Chain Derived from Binary Relevance

2014 ◽  
Vol 551 ◽  
pp. 302-308
Author(s):  
Tao Guo ◽  
Gui Yang Li
Keyword(s):  
Double Layer ◽  
Classification Problem ◽  
Classification Methods ◽  
Improved Method ◽  
Binary Relevance ◽  
Space Experiments ◽  
Benchmark Datasets ◽  
Label Correlations ◽  
Two Stages ◽  
Attribute Space

In multi-label classification, each training example is associated with a set of labels and the task for classification is to predict the proper label set for each unseen instance. Recently, multi-label classification methods mainly focus on exploiting the label correlations to improve the accuracy of individual multi-label learner. In this paper, an improved method derived from binary relevance named double layer classifier chaining (DCC) is proposed. This algorithm decomposes the multi-label classification problem into two stages classification process to generate classifier chain. Each classifier in the chain is responsible for learning and predicting the binary association of the label given the attribute space, augmented by all prior binary relevance predictions in the chain. This chaining allows DCC to take into account correlations in the label space. Experiments on benchmark datasets validate the effectiveness of proposed approach comparing with other well-established methods.

scholarly journals Improved Preimage Attacks on 4-Round Keccak-224/256

2021 ◽  
pp. 217-238
Author(s):  
Le He ◽  
Xiaoen Lin ◽  
Hongbo Yu
Keyword(s):  
Theoretical Analysis ◽  
Degrees Of Freedom ◽  
Linear Structure ◽  
Linearization Method ◽  
Partial Linearization ◽  
Practical Complexity ◽  
Partial Linearization Method ◽  
Preimage Attack

This paper provides an improved preimage attack method on standard 4-round Keccak-224/256. The method is based on the work pioneered by Li and Sun, who design a linear structure of 2-round Keccak-224/256 with 194 degrees of freedom left. By partially linearizing 17 output bits through the last 2 rounds, they finally reach a complexity of 2207/2239 for searching a 4-round preimage. Yet under their strategy, those 17 bits are regarded as independent bits and the linearization costs a great amount of freedom. Inspired by their thoughts, we improve the partial linearization method where multiple output bits can reuse some common degrees of freedom. As a result, the complexity of preimage attack on 4-round Keccak-224/256 can be decreased to 2192/2218, which are both the best known theoretical preimage cryptanalysis so far. To support the theoretical analysis, we apply our strategy to a 64-bit partial preimage attack within practical complexity. It is remarkable that this partial linearization method can be directly applied if a better linear structure with more freedom left is proposed.

Identification of the Damping Matrix

2001 ◽  
Author(s):  
Menahem Baruch
Keyword(s):  
Frequency Response Function ◽  
Degrees Of Freedom ◽  
Linear Structure ◽  
Dynamic Structure ◽  
Viscous Damping ◽  
Structural System ◽  
Linear Dynamic ◽  
Damping Matrix ◽  
Stiffness Matrices ◽  
Mass Matrices

Abstract Only experiments can provide the data necessary to obtain the damping matrix of a dynamic structural system. In the method proposed here the damping matrix can be separated from the mass and stiffness matrices and obtained in an independent of them way. Two methods are presented. In the first method it is assumed that all the degrees of freedom can be loaded and measured. Several methods for calculation of the damping, mass and stiffness matrices, using the experimental data are presented. In the second method the load is employed only in some chosen points. However, it is assumed again that all the degrees of freedom are measured. In order to identify the damping, stiffness and mass matrices of the structure the measured quantities are forced to comply with the general laws for a linear structure. The structure is idealized to be a linear dynamic structure with viscous damping. The measured quantities are measured during the tests at discrete points of the Frequency Response Function.

A Fuzzy Logic-Based System for Controlling the Temperature of Steam Exiting a Superheater for the Purpose of Preemptive Perturbation Compensation

2021 ◽  
Vol 22 (4) ◽  
pp. 181-190
Author(s):  
M. Yu. Ryabchikov ◽  
E. S. Ryabchikova ◽  
S. A. Filippov
Keyword(s):  
Fuzzy Logic ◽  
Control System ◽  
Negative Feedback ◽  
Degrees Of Freedom ◽  
Fuzzy Controller ◽  
Linear Structure ◽  
Transition Process ◽  
Smith Predictor ◽  
Steam Temperature ◽  
The Impact

This paper discusses the issue of adjusting the temperature of steam exiting a superheater in an environment that is affected by perturbations due to the sudden and significant fluctuations in the inlet steam temperature. Using the superheater at the Magnitogorsk Iron & Steel Works as an example, we highlight that a slow response to the aforementioned perturbations in the systems that adjust for deviations leads to undesired rises and drops in the outlet steam temperature. We review the current suggestions on adjusting the temperature of steam exiting a superheater and determine the main reasons behind the drop in adjustment quality. These reasons are related to a significant lag and the variability of the control object’s features, which make preemptive perturbation control difficult. In order to control such environments, we propose a system with two degrees of freedom, which combines a proportional-integral controller and a fuzzy logic-based controller. In the system that we are proposing, the changes in the controlled parameter (depending on the input value) are adjusted within the main loop that has a standard controller and negative feedback, while the perturbations are removed by using a secondary loop, which also has negative feedback, a fuzzy logic-based controller, and a simulation of the object without the component that accounts for the lag. For situations when the information on the object’s features is precise, we describe the specifics of the loops’ interaction, specifically in cases when the task processing loop does not respond to the perturbations in the inlet steam temperature, thus allowing for setting up the loops’ controllers separately. In situations when the inlet steam temperature is experiencing perturbations, the impact of the lag on adjustment quality only becomes evident when the trajectory of the transition process shifts along the time scale by a lag value, which is completely in line with the Smith predictor principles. The system is focused on synthesizing the fuzzy logic rules and refining the parameters of the simulation used for adjustment purposes, based on the results of automated computer-aided control simulation. We propose a structural modification of the control system that makes it possible to compensate for any residual control errors caused by the non-linear structure of the fuzzy controller; this reduces the number of requirements for those set-up parameters where the value selection is based on the needs of simulation modeling, which requires a lot of computing resources. We demonstrate the results of simulation experiments that compare the efficiency of control using the system suggested and the efficiency of control using a system with a standard controller only. The computer simulation was performed in the MATLAB Simulink environment. We reaffirm that a combined control system performs better when adjusting the steam temperature.

An Improved Method of Matrix Displacement Analysis in Vibration Problems

1969 ◽  
Vol 20 (4) ◽  
pp. 321-332 ◽  
Author(s):  
W. Carnegie ◽  
J. Thomas ◽  
E. Dokumaci
Keyword(s):  
Strong Convergence ◽  
Degrees Of Freedom ◽  
Continuous Medium ◽  
Continuous Systems ◽  
Improved Method ◽  
Eigenvalues And Eigenvectors ◽  
Displacement Method ◽  
Vibration Problems ◽  
Number Of Segments

SummaryThis paper presents a method with strong convergence characteristics for the determination of eigenvalues and eigenvectors of continuous systems. The limitation on the number of undetermined constants in the displacement functions introduced by the conditions at the ends of a segment is removed by the introduction of points of freedom within the segment.This improves the convergence of eigenvalues and eigenvectors very rapidly with the number of segments, especially in torsional vibration problems where the convergence with the usual Matrix Displacement method is very poor. The continuous medium is successively approximated by the use of sub-systems with finite numbers of degrees of freedom. The principles upon which the method is based and the convergence of the results are discussed and illustrated by a series of examples.

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