6,256 research outputs found
A Simple Attack on Some Clock-Controlled Generators
We present a new approach to edit distance attacks on certain
clock-controlled generators, which applies basic concepts of Graph Theory to
simplify the search trees of the original attacks in such a way that only the
most promising branches are analyzed. In particular, the proposed improvement
is based on cut sets defined on some graphs so that certain shortest paths
provide the edit distances. The strongest aspects of the proposal are that the
obtained results from the attack are absolutely deterministic, and that many
inconsistent initial states of the target registers are recognized beforehand
and avoided during search
Graph-Based Approach to the Edit Distance Cryptanalysis of Irregularly Clocked Linear Feedback Shift Registers
This paper proposes a speed-up of a known-plaintext attack on some stream ciphers
based on Linear Feedback Shift Registers (LFSRs). The algorithm consists of two basic steps:
first, to guess the initial seed value of one of the LFSRs, and then to use the resulting binary
sequence in order to deduce useful information about the cipher parameters. In particular, the
proposed divide-and-conquer attack is based on a combination of graph-based techniques with
edit distance concepts. While the original edit distance attack requires the exhaustive search over
the set of all possible initial states of the involved LFSR, this work presents a new heuristic optimization
that avoids the evaluation of an important number of initial states through the identification
of the most promising branches of the search graph. The strongest aspects of the proposal
are the facts that the obtained results from the attack are absolutely deterministic, and that many
inconsistent initial states of the target LFSRs are recognized and avoided during search.This work was supported by the Spanish Ministry of Science and Innovation and European
FEDER Fund under Project TIN2008-02236/TSI as well as by CDTI (Spain)and the companies INDRA, Unin Fenosa, Tecnobit, Visual Tool, Brainstorm, SAC and
Technosafe under Project Cenit-HESPERIA.Peer reviewe
Integrated chaos generators
This paper surveys the different design issues, from mathematical model to silicon, involved on the design of integrated circuits for the generation of chaotic behavior.Comisión Interministerial de Ciencia y Tecnología 1FD97-1611(TIC)European Commission ESPRIT 3110
Graph-Based Approach to the Edit Distance Cryptanalysis of Irregularly Clocked Linear Feedback Shift Registers
This paper proposes a speed-up of a known-plaintext attack on some stream ciphers
based on Linear Feedback Shift Registers (LFSRs). The algorithm consists of two basic steps:
first, to guess the initial seed value of one of the LFSRs, and then to use the resulting binary
sequence in order to deduce useful information about the cipher parameters. In particular, the
proposed divide-and-conquer attack is based on a combination of graph-based techniques with
edit distance concepts. While the original edit distance attack requires the exhaustive search over
the set of all possible initial states of the involved LFSR, this work presents a new heuristic optimization
that avoids the evaluation of an important number of initial states through the identification
of the most promising branches of the search graph. The strongest aspects of the proposal
are the facts that the obtained results from the attack are absolutely deterministic, and that many
inconsistent initial states of the target LFSRs are recognized and avoided during search.This work was supported by the Spanish Ministry of Science and Innovation and European
FEDER Fund under Project TIN2008-02236/TSI as well as by CDTI (Spain)and the companies INDRA, Unin Fenosa, Tecnobit, Visual Tool, Brainstorm, SAC and
Technosafe under Project Cenit-HESPERIA.Peer reviewe
AC OPF in Radial Distribution Networks - Parts I,II
The optimal power-flow problem (OPF) has played a key role in the planning
and operation of power systems. Due to the non-linear nature of the AC
power-flow equations, the OPF problem is known to be non-convex, therefore hard
to solve. Most proposed methods for solving the OPF rely on approximations that
render the problem convex, but that may yield inexact solutions. Recently,
Farivar and Low proposed a method that is claimed to be exact for radial
distribution systems, despite no apparent approximations. In our work, we show
that it is, in fact, not exact. On one hand, there is a misinterpretation of
the physical network model related to the ampacity constraint of the lines'
current flows. On the other hand, the proof of the exactness of the proposed
relaxation requires unrealistic assumptions related to the unboundedness of
specific control variables. We also show that the extension of this approach to
account for exact line models might provide physically infeasible solutions.
Recently, several contributions have proposed OPF algorithms that rely on the
use of the alternating-direction method of multipliers (ADMM). However, as we
show in this work, there are cases for which the ADMM-based solution of the
non-relaxed OPF problem fails to converge. To overcome the aforementioned
limitations, we propose an algorithm for the solution of a non-approximated,
non-convex OPF problem in radial distribution systems that is based on the
method of multipliers, and on a primal decomposition of the OPF. This work is
divided in two parts. In Part I, we specifically discuss the limitations of BFM
and ADMM to solve the OPF problem. In Part II, we provide a centralized version
and a distributed asynchronous version of the proposed OPF algorithm and we
evaluate its performances using both small-scale electrical networks, as well
as a modified IEEE 13-node test feeder
Modified Alternating Step Generators
Irregular clocking of feedback shift registers is a popular technique to improve parameters of keystream generators in stream ciphers. Another technique is to implement nonlinear functions. We join these techniques and propose Modified Alternating Step Generators built with linear and nonlinear feedback shift registers. Adequate nonlinear Boolean functions are used as feedbacks or as filtering functions of shift registers in order to increase complexity of sequences produced by individual registers and the whole generator. We investigate basic parameters of proposed keystream generators, such as period, linear complexity and randomness
The Role of Reflexes Versus Central Pattern Generators
Animals execute locomotor behaviors and more with ease. They have evolved these breath-taking abilities over millions of years. Cheetahs can run, dolphins can swim and flies can fly like no artificial technology can. It is often argued that if human technology could mimic nature, then biological-like performance would follow. Unfortunately, the blind copying or mimicking of a part of nature [Ritzmann et al., 2000] does not often lead to the best design for a variety of reasons [Vogel, 1998]. Evolution works on the just good enough principle. Optimal designs are not the necessary end product of evolution. Multiple satisfactory solutions can result in similar performances. Animals do bring to our attention amazing designs, but these designs carry with them the baggage of their history. Moreover, natural design is constrained by factors that may have no relationship to human engineered designs. Animals must be able to grow over time, but still function along the way. Finally, animals are complex and their parts serve multiple functions, not simply the one we happen to examine. In short, in their daunting complexity and integrated function, understanding animal behaviors remains as intractable as their capabilities are tantalizing
Grein. A New Non-Linear Cryptoprimitive
In this thesis, we will study a new stream cipher, Grein, and a new cryptoprimitive used in this cipher. The second chapter gives a brief introduction to cryptography in general. The third chapter looks at stream ciphers in general, and explains the advantages and disadvantages of stream ciphers compared to block ciphers. In the fourth chapter the most important building blocks used in stream ciphers are explained. The reader is excepted to know elementary abstract algebra, as much of the results in this chapter depend on it. In the fifth chapter, the stream cipher Grain is introduced. In chapter six, the new stream cipher, Grein, is introduced. Here, we look at the different components used in the cipher, and how they operate together. In chapter seven, we introduce an alteration to the Grein cryptosystem, which hopefully have some advantagesMaster i InformatikkMAMN-INFINF39
Sequential pulse generator for the thyristor control of induction machines and reversible rectifiers
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