|
|
Cryptanalytic attacks on lightweight ciphers
Rabas, Tomáš ; Göloglu, Faruk (advisor) ; Kozlík, Andrew (referee)
In 2016 the National Institute of Standards and Technology (NIST) started the stan- dardization process for lightweight cryptography (LWC). We provide a broad introduc- tion to lightweight cryptography together with a survey of current design trends and lightweight cryptography standards, with special attention to this competition. In the second part, we present a description and cryptoanalysis of three lightweight ciphers: SIV-Rijndael256, CLX, and Limdolen. 1
|
|
|
On a matrix approach for constructing quadratic almost perfect nonlinear functions
Rezková, Zuzana ; Göloglu, Faruk (advisor) ; Žemlička, Jan (referee)
Search for new APN functions is an important topic in symmetric cryptography. The matrix approach for constructing quadratic APN functions was described by Y. Yu, M. Wang and Y. Li in 2014. The approach takes advantage of the one to one correspondence between quadratic homogenous APN functions and quadratic APN matrices. The aim of this thesis is to explain the matrices used in the original paper and show that similar matrices can be constructed directly from the algebraic normal form of the APN function. In Chapter 2 we introduce the original method adding extra theorems and expanding the proofs for better understanding. In Chapter 3 we define the matrices obtained simply from the algebraic normal form. In Chapter 4 we give examples of the matrices for chosen APN functions and show how they are related. 1
|
|
|
Multiplication in a finite field of characteristic 2 and XOR-metrics
Carulkov, Nikita Edward ; Žemlička, Jan (advisor) ; Göloglu, Faruk (referee)
XOR-counts measure the efficiency of multiplication in finite fields of characteristic 2. In the first chapter we define two XOR-counts (the direct XOR-count and the sequential XOR-count) and present detailed proofs of some propositions from the paper from Lukas Kolsch about the XOR-counts of inverse matrices and permutation similar matrices. It seems that the case when the direct XOR-count is lower than the sequential XOR-count is rare. We will explore those cases in the second chapter. Some of them were already described in the paper from Lukas Kolsch and we prove that they occur only for matrices with order higher or equal to six. 1
|
|
|
A study on ``A New Public-Key Cryptosystem via Mersenne Numbers''
Richter, Filip ; Göloglu, Faruk (advisor) ; El Bashir, Robert (referee)
In 2016 NIST announced a start of a process of development and standardiza- tion of a post-quantum public-key encryption scheme. Mersenne-756839 was one of the proposals. This proposal is described in this thesis, as well as the known attacks against it. The description and the theoretical background behind these attacks are presented in a rigorous way and are accessible to the reader without any previous knowledge about the post-quantum cryptography. New additional ideas for the implementation of the attacks are also presented. Finally, these attacks are implemented and attached to the thesis. 1
|
|
|
APN functions with non-classical Walsh spectra
Maršálek, Michal ; Göloglu, Faruk (advisor) ; Drápal, Aleš (referee)
An interesting class of Boolean functions are APN functions - these func- tions are "as far" from linear functions as possible. Most of the quadratic APN functions have the same (=classical) Walsh spectrum - a sort of footprint of the function. The aim of this thesis is to describe a method which might lead to a generalisation of a sporadic example of a quadratic APN function with non-classical Walsh spectrum. Up until recently, it was believed that no such function exists. This was proven to be false in 2009, as an example of such func- tion in dimension 6 was introduced. In this thesis, we describe the construction and then deduce necessary conditions for some free coefficients in order to reduce the search space to a level which enables a computer search. 1
|
|
|
Hledání APN permutací ve známých APN funkcích
Pavlů, Jiří ; Göloglu, Faruk (advisor) ; Drápal, Aleš (referee)
In the thesis a new way of checking whether a function is CCZ-equivalent to a permutation is given. The results for known families of almost perfect nonlinear (APN) functions are presented for functions defined over GF(2n ), for even n ≤ 12. The ways how to reduce the number of polynomials from each family are studied. For functions of the form x3 + a-1 tr1(a3 x9 ) it is shown, that they cannot be CCZ-equivalent to a permutation on fields GF(24n ) for n ∈ ℕ .
|
|
|
Constructions of APN permutations
Krasnayová, Dáša ; Göloglu, Faruk (advisor) ; Lisoněk, Petr (referee)
In this thesis, we examine a family of vectorial boolean functions on F22m inspired by Kim function, in order to find new APN permutations on F22m for m > 2. The functions of this family are defined as F(X) = X3 + bX3q + cX2q+1 + dXq+2 , where parameters b, c and d are from F2m . Necessary and sufficient conditions for this functions to be APN or equivalent to a permutation are presented in this thesis. To find conditions for being APN, Trace-0/Trace-1 decomposition method is used. A method using exponential sums is used to deduce which functions of this family is CCZ-equivalent to a certain type of permutation. These results were then used to search for APN permutations on F26 and F210 . 1
|
|
|
Relationship between higher order attacks and CCZ-equivalence
Deptová, Lucie ; Göloglu, Faruk (advisor) ; Hojsík, Michal (referee)
In this thesis, we explain the term CCZ-equivalence in more detail to- gether with an analysis of a special type of matrices of this equivalence. We also clarify the higher order differential cryptanalysis and its generalized ver- sion. To demonstrate this method we present several attacks on a simple five round Feistel cipher, two of these attacks are our own. We have implemented the most important attacks and results of these experiments can be found in the text. We also explore how to use a decomposition F = F2 ◦F−1 1 (where F1 and F2 are permutations) to construct a generalized higher order differential attack to a block cipher with an S-box F. This construction may be used while searching for an attack to F using the CCZ-equivalence which is gener- ally a hard question. The result of our research is a theorem which presents a necessary condition on a degree of F which is needed for an existence of such a decomposition. 1
|
|
|
Algebraic-differential analysis of Keccak
Seidlová, Monika ; Göloglu, Faruk (advisor) ; Hojsík, Michal (referee)
In this thesis, we analyze the cryptographic sponge function family Keccak - the winner of the SHA-3 Cryptographic Hash Standard competition. Firstly, we explore how higher order differentials can be used to forge a tag in a parallelizable MAC function. We introduce new terms and theory studying what affine spaces remain affine after one round of Keccak's underlying permutation Keccak-f. This allows us to improve the forgery. Secondly, collisions in Keccak could be generated from pairs of values, that follow particular differential trails in Keccak-f. We tested finding pairs for a given differential trail in reduced-round Keccak-f using algebraic techniques with the mathematics software SAGE. We found a pair in a 4-round trail in Keccak-f[50] in under 5 minutes and a 3-round trail in Keccak-f[100] in 80 seconds on a regular PC. Powered by TCPDF (www.tcpdf.org)
|
|
|
Links Between Differential and Linear Cryptanalysis
Töpfer, Jakub ; Hojsík, Michal (advisor) ; Göloglu, Faruk (referee)
This thesis concerns the relations between correlation matrix, difference propagation matrix and other matrices used in the block cipher cryptanalysis. We show that some relations between these matrices can be seen just as a change of basis provided by the discrete Fourier transform. This can be used for an easier proof of a well-known theorem. We also study properties of difference propagation matrix, describe a class of vectorial Boolean functions which have the same difference propagation matrix and state a numerically justified hypothesis that this class contains all such functions.
|
guest ::
