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Academic collection --- 681.3*E3 --- Data encryption: data encryption standard; DES; public key cryptosystems --- Theses --- 681.3*E3 Data encryption: data encryption standard; DES; public key cryptosystems

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Secure message transmission is of extreme importance in today's information-based society. Stream encryption is a practically important means to this end. This monograph is devoted to a new aspect of stream ciphers, namely the stability theory of stream ciphers, with the purpose of developing bounds on complexity which can form part of the basis for a general theory of data security and of stabilizing stream-cipher systems. The approach adopted in this monograph is new. The topic is treated by introducing measure indexes on the security of stream ciphers, developing lower bounds on these indexes, and establishing connections among them. The treatment involves the stability of boolean functions, the stability of linear complexity of key streams, the period stability of key streams, and the stability of source codes. Misleading ideas about stream ciphers are exposed and new viewpoints presented. The numerous measure indexes and bounds on them that are introduced here, the approach based on spectrum techniques, andthe ten open problems presented will all be useful to the reader concerned with analyzing and designing stream ciphers for securing data.

Bedieningstheorie --- Chiffres --- Cijfers --- Ciphers --- Commande [Theorie de la ] --- Control theory --- Stabiliteit --- Stability --- Stabilité --- Chiffres (Cryptographie) --- Théorie de la commande --- 681.3*E3 --- Dynamics --- Mechanics --- Motion --- Vibration --- Benjamin-Feir instability --- Equilibrium --- Machine theory --- Codes --- Contractions --- Signs and symbols --- Symbolism --- Abbreviations --- Code names --- Cryptography --- Writing --- Data encryption: data encryption standard; DES; public key cryptosystems --- 681.3*E3 Data encryption: data encryption standard; DES; public key cryptosystems --- Théorie de la commande --- Stabilité --- Stream ciphers --- State ciphers --- Control theory. --- Stability. --- Ciphers. --- Data encryption (Computer science). --- Computer security. --- Operating systems (Computers). --- Numerical analysis. --- Cryptology. --- Systems and Data Security. --- Operating Systems. --- Numerical Analysis. --- Data encoding (Computer science) --- Encryption of data (Computer science) --- Computer security --- Mathematical analysis --- Computer operating systems --- Computers --- Disk operating systems --- Systems software --- Computer privacy --- Computer system security --- Computer systems --- Cyber security --- Cybersecurity --- Electronic digital computers --- Protection of computer systems --- Security of computer systems --- Data protection --- Security systems --- Hacking --- Operating systems --- Protection --- Security measures

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In deze thesis bestuderen we de bouwblokken van cryptografische systemen die gebruikt worden in symmetrische cryptografie. De bouwblokken kunnen gezien worden als Booleaanse functies voor een één dimensionale uitgang en vector Booleaanse functies, ook S(ubstitutie)-boxen genoemd, indien de uitgang meer dan één bit is. We beginnen met een gedetailleerde veiligheidsanalyse voor de filter-en combinatiegenerator, welke de twee meest voorkomende en bestudeerde stroomcijfers zijn. Uit deze analyse leiden we de minimale veiligheidsvereisten af voor de Booleaanse functie in de generator. Vervolgens bestuderen we het bestaan van dergelijke functies die tevens een efficiënte implementatie bezitten. Symmetrische functies en Booleaanse functies die afgeleid worden van bijectieve en sterk niet-lineaire machtfuncties worden hiervoor onderzocht. Om Booleaanse functies in het algemeen te bestuderen, leiden we eerst de affiene equivalentie klassen af voor Booleaanse functies in 5 variabelen en 6 en 7 variabelen met graad kleiner dan of gelijk aan 3. Uit deze classificatie volgen verschillende resultaten: nieuwe eigenschappen voor de maximaal resiliënte Booleaanse functies van graad 3, nieuwe exacte waarden en grenzen voor de afstand van een resiliënte functie tot functies van lagere graad, en het feit dat alle maximaal niet-lineaire functies in dimensie kleiner of gelijk aan 8 en graad kleiner of gelijk aan drie tot de Maiorana-McFarland klasse behoren. We bekijken ook de sterkte van twee vaak voorkomende bouwblokken in cryptografische algoritmen, namelijk de optelling en vermenigvuldiging in het veld. In het bijzonder stellen we compacte vergelijkingen op voor de niet-lineaire combinaties van hun uitgangscomponenten. De thesis wordt afgesloten met een veralgemening van verschillende cryptografische eigenschappen van Booleaanse functies door te werken in een nieuwe metriek. Deze nieuwe eigenschappen resulteren in een beter begrip van de eigenschappen van Booleaanse functies. Hierdoor kunnen we functies construeren waarvoor de veiligheid is uitgedrukt m.b.t. specifieke monotone verzamelingen in plaats van de veiligheid m.b.t. alle monotone verzamelingen met dezelfde cardinaliteit zoals in de gewone definities. Tenslotte tonen we in dit veralgemeende kader de verbanden aan tussen resiliënte functies enerzijds en foutverbeterende codes en orthogonale rijen anderzijds. This thesis deals with building blocks of cryptosystems in symmetric cryptography. The building blocks can be seen as Boolean functions for a one dimensional output and vectorial Boolean functions, also called S(ubstitution)-boxes, for a multi dimensional output. We start with a thorough security analysis of the filter and combination generator in order to derive the minimal requirements on the Boolean function in the generator. Then, we investigate the existence of efficiently implementable functions satisfying these requirements. For this purpose, we study the symmetric functions and the Boolean functions that are affine equivalent to the trace function of highly nonlinear bijective power functions. In order to study Boolean functions with a broader perspective, we derive the affine equivalence classes of Boolean functions in 5 variables and 6 and 7 variables of degree less than or equal to 3. From this classification, we find several new properties on maximum resilient cubic Boolean functions, distance of resilient functions to low degree functions, and cubic bent functions in less than or equal to 8 variables. We also study the strength of two building blocks which are frequently used in cryptographic algorithms, namely the addition and multiplication in a finite field. In particular, we derive a compact representation of the algebraic equations representing the nonlinear combinations of the output components of the S-boxes. Finally, by considering a new metric, we generalize several cryptographic properties of Boolean functions. The new definitions result in a better understanding of these properties and provide a better insight in the space defined by this metric. This approach leads to the construction of ''hand-made'' Boolean functions, i.e., functions for which the security with respect to some specific monotone sets of inputs is considered, instead of the security with respect to all possible monotone sets with the same cardinality, as in the usual definitions. We show relations between resilient Boolean functions, error-correcting codes, and orthogonal arrays in this generalized setting.

Academic collection --- 681.3*D46 <043> --- 681.3*E4 <043> --- 681.3*E4 <043> Coding and information theory: data compaction and compression formal modelsof communication nonsecret encoding schemes--See also {681.3*H11}--Dissertaties --- Coding and information theory: data compaction and compression formal modelsof communication nonsecret encoding schemes--See also {681.3*H11}--Dissertaties --- 681.3*D46 <043> Security and protection: access controls authentication cryptographic controls information flow controls security kernels verification (Operating systems)--Dissertaties --- Security and protection: access controls authentication cryptographic controls information flow controls security kernels verification (Operating systems)--Dissertaties --- Theses --- 681.3*E3 <043> --- Data encryption: data encryption standard; DES; public key cryptosystems--Dissertaties --- 681.3*E4 <043> Coding and information theory: data compaction and compression; formal modelsof communication; nonsecret encoding schemes--See also {681.3*H11}--Dissertaties --- Coding and information theory: data compaction and compression; formal modelsof communication; nonsecret encoding schemes--See also {681.3*H11}--Dissertaties --- 681.3*D46 <043> Security and protection: access controls; authentication; cryptographic controls; information flow controls; security kernels; verification (Operating systems)--Dissertaties --- Security and protection: access controls; authentication; cryptographic controls; information flow controls; security kernels; verification (Operating systems)--Dissertaties