Exact relation between nonlinearity and algebraic immunity

We describe the algebraic immunity and calculation of algebraic immunity of boolean functions. We propose a new balanced n-variable boolean function with high algebraic immunity. We check the nonlinearity of the new function for n < 20 and the algebraic immunity of the function in case of n < 18. We conjecture it has optimum algebraic immunity.

Nowadays, the resistance against algebraic attacks and fast algebraic attacks are considered as an important cryptographic property for Boolean functions used in stream ciphers. Both attacks are very powerful analysis concepts and can be applied to symmetric cryptographic algorithms used in stream ciphers. The notion of algebraic immunity has received wide attention since it is a powerful tool to measure the resistance of a Boolean function to standard algebraic attacks. Nevertheless, an algebraic tool to handle the resistance to fast algebraic attacks is not clearly identified in the literature. In the current paper, we propose a new parameter to measure a Boolean function's resistance to fast algebraic attack. We also introduce the notion of fast immunity profile and show that it informs both on the resistance to standard and fast algebraic attacks. Further, we evaluate our parameter for two secondary constructions of Boolean functions. Moreover, A coding-theory approach to the characterization of perfect algebraic immune functions is presented. Via this characterization, infinite families of binary linear complementary dual codes (or LCD codes for short) are obtained from perfect algebraic immune functions. Some of the binary LCD codes presented in this paper are optimal. These binary LCD codes have applications in armoring implementations against so-called side-channel attacks (SCA) and fault non-invasive attacks, in addition to their applications in communication and data storage systems.

Cryptography plays an important role in the network environment and wireless applications. Most of the time, the information in wireless and network environment is encrypted by stream ciphers which must resist many kinds of attacks. Algebraic immunity (AI) is one of the most important characteristics which evaluate the resistance against algebraic attacks. Constructing a Boolean function which has both AI and other crypto characteristics is an important studying field. In this paper, we study the AI and other properties, and then propose a construction method based on genetic algorithm that can obtain Boolean functions with good cryptographic appearance.

Algebraic immunity is a new cryptographic criterion proposed to against algebraic attacks. In order to resist algebraic attacks, Boolean functions used in cryptosystem should have high algebraic immunity. This paper presents a construction for even-variable Boolean function with optimum algebraic immunity.

Boolean functions with a variety of secure cipher properties are the key factors to design cryptosystem with the ability to resist multiple cipher attacks and good safety performance. In this paper, using the derivative of the Boolean functions and the e-derivative defined by ourselves as the main research tools, we study algebraic immunity, correlation immunity and other cryptographic properties of the quadratic rotation symmetric Boolean functions. We determine the quadratic rotation symmetric Boolean functions which are H Boolean functions, and the range of weight distribution of the quadratic rotation symmetry H Boolean functions. Besides, we get the compatibility among propagation, balance, correlation immunity and algebraic immunity of the quadratic rotation symmetry H Boolean functions, and also focus on the relationship of balance, correlation immunity and dimension. Furthermore, we check the existence of the cubic rotation symmetry H Boolean functions, and obtain the relationship between existence and dimension of the cubic rotation symmetry H Boolean functions. Moreover, we obtain a more convenient method for solving annihilator. Such researches are important in cryptographic primitive designs, and have significance and role in the theory and application range of cryptosystems.

Results on highly nonlinear Boolean functions with provably good immunity to fast algebraic attacks

In this paper, we study the algebraic immunity of Boolean functions and consider in particular the problem of constructing Boolean functions with a good algebraic immunity. We first give heuristic arguments which seem to indicate that the algebraic immunity of a random Boolean function on n variables is at least lfloorn/2rfloor with a very high probability (while the upper bound is lceiln/2rceil, the "ceiling" of n/2). We give an upper bound, under a reasonable assumption, on the algebraic immunity of Boolean functions constructed through Maiorana-MacFarland construction. At last we give examples of balanced functions with optimal algebraic immunity and a good nonlinearity and of balanced functions with a good algebraic immunity, a good nonlinearity and a good correlation immunity, which can be used for cryptographic purposes

We go deep into the internal structure of the Boolean functions values, and study the relationship of algebraic immunity and algebraic degree of Boolean functions with the Hamming weight with the diffusion included. Then we get some theorems which relevance together algebraic immunity, annihilators and algebraic degree of H Boolean functions by the e-derivative which is a part of the H Boolean function. Besides, we also get the results that algebraic immunity and algebraic degree of Boolean functions can be linked together by the e-derivative of H Boolean functions and so on.

Algebraic immunity is an important cryptographic property for Boolean functions against algebraic attacks. Constructions of Boolean functions with the maximum algebraic immunity (MAI Boolean functions) by using univariate polynomial representation of Boolean functions over finite fields have received more and more attention. In this paper, how to obtain more MAI Boolean functions from a known MAI Boolean function under univariate polynomial representation is further investigated. The sufficient condition of Boolean functions having the maximum algebraic immunity obtained by changing a known MAI Boolean function under univariate polynomial representation is given. With this condition, more balanced MAI Boolean functions under univariate polynomial representation can be obtained. The algebraic degree and the nonlinearity of these Boolean functions are analyzed.

Boolean functions are used as nonlinear filter functions and combiner functions in several stream ciphers. The security of these stream ciphers largely depends upon cryptographic properties of Boolean functions. Finding a balanced Boolean function with optimal cryptographic properties is an open research problem in the cryptographic community. Since the number of n-variable Boolean functions is $$2^{2^n}$$ , it is not computationally feasible to search the entire space of such functions for cryptographically significant functions when $$n \ge 6$$ . In general, the construction of Boolean functions with optimal or near optimal cryptographically significant properties is formulated as combinatorial optimization problems. In this paper, we apply the Genetic algorithm with the integration of a local search procedure called hybrid GA (HGA) searching for the Boolean functions with high nonlinearity and low autocorrelation. The performance of the Genetic algorithm depends upon the tuning parameters such as crossover mechanism, mutation probability, selection criteria, and the choice of fitness/cost function. To achieve an optimal trade-off among two cryptographic properties, the choice of the cost function plays an important role for finding an optimal solution. So our main focus is to construct balanced Boolean functions using HGA with a new cost function and compare it with existing cost functions. Our experimental results shows that the HGA is more efficient than GA and the new cost function is more efficient than existing cost functions for reaching the optimal solutions.

Boolean functions play a central role in the security of stream and block ciphers (in symmetric cryptography). They are functions mapping binary vectors of some length to either bits (in which case we have Boolean functions strictly speaking) or to binary vectors (of the same length or of another length, we are then speaking of vectorial Boolean functions). In the first case, they play roles in stream ciphers and in the second case, they are mainly used as substitution boxes in block ciphers. Being in each case the only nonlinear components of the ciphers, they are essential to their security. They are also the main components of the ciphers whose choice induces the speed. A tradeoff must then be found between the security and the speed of the cipher. The AES winner (used nowadays as a NIST standard for civil encryption, in particular between all banks) has been chosen because it allowed the best tradeoff. We shall describe what are the main results on them and what are the main open problems they pose currently.

After the improvement by Courtois and Meier of the algebraic attacks on stream ciphers and the introduction of the related notion of algebraic immunity, several constructions of infinite classes of Boolean functions with optimum algebraic immunity have been proposed. All of them gave functions whose algebraic degrees are high enough for resisting the Berlekamp-Massey attack and the recent Ronjom-Helleseth attack, but whose nonlinearities either achieve the worst possible value (given by Lobanov's bound) or are slightly superior to it. Hence, these functions do not allow resistance to fast correlation attacks. Moreover, they do not behave well with respect to fast algebraic attacks. In this paper, we study an infinite class of functions which achieve an optimum algebraic immunity. We prove that they have an optimum algebraic degree and a much better nonlinearity than all the previously obtained infinite classes of functions. We check that, at least for small values of the number of variables, the functions of this class have in fact a very good nonlinearity and also a good behavior against fast algebraic attacks.

Filter generators form one of the best known and most studied classes of key stream generators used in synchronous stream ciphers. Each such generator consists of a binary linear shift register with a primitive feedback polynomial and a nonlinear Boolean function, which has a number of requirements related to the condition of generator security against known attacks. One such requirement is the high algebraic immunity of the generator's filter function; this parameter characterises security filter generator against modern algebraic attacks. In certain cases, this requirement is too restrictive in sense of practicality, as it increases the computational or circuit complexity of the key stream generation algorithm. This makes the actuality of increasing the resistance of filter generators with fixed filter functions, that have limited (low) algebraic immunity. The paper proposes to solve this problem by modifying the feedback function of the linear shift register. the security of the proposed generators against algebraic attacks is investigated and is shown that (under certain natural conditions) such generators are more secure at the same initial state length as compared to traditional filter generators. The proposed solution seems to be useful for practical application in advanced hardware-oriented stream ciphers design.

Since 1970, Boolean functions have been the focus of a lot of attention in cryptography. An important topic in symmetric ciphers concerns the cryptographic properties of Boolean functions and constructions of Boolean functions with good cryptographic properties, that is, good resistance to known attacks. An important progress in cryptanalysis areas made in 2003 was the introduction by Courtois and Meier of algebraic attacks and fast algebraic attacks which are very powerful analysis concepts and can be applied to almost all cryptographic algorithms. To study the resistance against algebraic attacks, the notion of algebraic immunity has been introduced. In this paper, we use a parameter introduced by Liu and al., called fast algebraic immunity, as a tool to measure the resistance of a cryptosystem (involving Boolean functions) to fast algebraic attacks. We prove an upper bound on the fast algebraic immunity. Using our upper bound, we establish the weakness of trace inverse functions against fast algebraic attacks confirming a recent result of Feng and Gong.

Given a positive integer n, let and . The generator matrix of the kth-order Reed–Muller code RM is an important tool in the study of Boolean functions' algebraic immunity. In this paper, choosing the last s column vectors in as a basis of the vector space , we study the values of the coefficients in the linear expressions of 's column vectors over this basis. As an application, we present a new construction of balanced even-variable Boolean functions on with optimal algebraic immunity by modifying the outputs of majority function. The nonlinearities of these constructed functions are also determined.