Bitwise Linear Mappings with Good Cryptographic Properties and Efficient Implementation

Linear mappings are crucial components of symmetric ciphers. A special type of linear mappings are (0,1)-matrices which have been used in symmetric ciphers such as ARIA, E2 and Camellia as diffusion layers with efficient implementation. Bitwise linear maps are also used in symmetric ciphers such as SHA family of hash functions and HC family of stream ciphers. In this article, we investigate a special kind of linear mappings: based upon this study, we propose several linear mappings with only XOR and rotation operations. The corresponding matrices of these mappings can be used in either the former case as (0,1)-matrices of maximal branch number or in the latter case as linear mappings with good cryptographic properties. The proposed mappings and their corresponding matrices can be efficiently implemented both in software and hardware

A More Explicit Formula for Linear Probabilities of Modular Addition Modulo a Power of Two

Linear approximations of modular addition modulo a power of two was studied by Wallen in 2003. He presented an efficient algorithm for computing linear probabilities of modular addition. In 2013 Sculte-Geers investigated the problem from another viewpoint and derived a somewhat explicit for these probabilities. In this note we give a closed formula for linear probabilities of modular addition modulo a power of two, based on what Schlte-Geers presented: our closed formula gives a better insight on these probabilities and more information can be extracted from it

Characterization of MDS mappings

MDS codes and matrices are closely related to combinatorial objects like orthogonal arrays and multipermutations. Conventional MDS codes and matrices were defined on finite fields, but several generalizations of this concept has been done up to now. In this note, we give a criterion for verifying whether a map is MDS or not

Statistical Properties of the Square Map Modulo a Power of Two

The square map is one of the functions that is used in cryptography. For instance, the square map is used in Rabin encryption scheme, block cipher RC6 and stream cipher Rabbit, in different forms. In this paper we study a special case of the square map, namely the square function modulo a power of two. We obtain probability distribution of the output of this map as a vectorial Boolean function. We find probability distribution of the component Boolean functions of this map. We present the joint probability distribution of the component Boolean functions of this function. We introduce a new function which is similar to the function that is used in Rabbit cipher and we compute the probability distribution of the component Boolean functions of this new map

Generalization of Statistical Criteria for Sboxes

Linear and differential cryptanalysis and their generalizations are the most important tools in ststistical analysis of symmetric ciphers. These attacks make use of linear and differential properties of Sboxes and component functions of symmetric ciphers. In this article, we investigate generalized statistical properties for Sboxes. We justify the application of linear, differential and differential-linear cryptanalysis from the mathematical viewpoint. We verify some well-known Sboxes and vectotial Boolean functions by the proposed criteria and show that these functions have larger biases compared with previous criteria presentesd up to now

Cryptographic Properties of Addition Modulo 2n2^n

The operation of modular addition modulo a power of two is one of the most applied operations in symmetric cryptography. For example, modular addition is used in RC6, MARS and Twofish block ciphers and RC4, Bluetooth and Rabbit stream ciphers. In this paper, we study statistical and algebraic properties of modular addition modulo a power of two. We obtain probability distribution of modular addition carry bits along with conditional probability distribution of these carry bits. Using these probability distributions and Markovity of modular addition carry bits, we compute the joint probability distribution of arbitrary number of modular addition carry bits. Then, we examine algebraic properties of modular addition with a constant and obtain the number of terms as well as algebraic degrees of component Boolean functions of modular addition with a constant. Finally, we present another formula for the ANF of the component Boolean functions of modular addition modulo a power of two. This formula contains more information than representations which are presented in cryptographic literature, up to now

Construction of New Families of ‎MDS‎ Diffusion Layers

Diffusion layers are crucial components of symmetric ciphers‎. ‎These components‎, ‎along with suitable Sboxes‎, ‎can make symmetric ciphers resistant against statistical attacks like linear and differential cryptanalysis‎. ‎Conventional ‎‎MDS diffusion layers, which are defined as matrices over finite fields, have been used in symmetric ciphers such as AES‎, ‎Twofish and SNOW‎. ‎In this paper‎, ‎we study linear, linearized and nonlinear MDS diffusion layers‎. We investigate linearized diffusion layers, ‎which are a generalization of conventional diffusion layers‎; t‎hese diffusion layers are used in symmetric ciphers like SMS4‎, ‎Loiss and ZUC‎. W‎e introduce some ‎new ‎families of linearized MDS diffusion layers ‎and as a consequence, ‎we ‎present a‎ ‎method ‎for ‎construction of ‎‎‎‎randomized linear ‎‎‎‎‎diffusion ‎layers over a finite field. Nonlinear MDS diffusion layers are introduced in Klimov\u27s thesis; we investigate nonlinear MDS diffusion layers theoretically, and we present a new family of nonlinear MDS diffusion layers. We show that these nonlinear diffusion layers can be made randomized with a low ‎implementatio‎n cost. An important fact about linearized and nonlinear diffusion layers is that they are more resistant against algebraic attacks in comparison to conventional diffusion layers. A ‎special case of diffusion layers are ‎‎‎(0,1)‎-‎diffusion layers. This type of diffusion layers are used in symmetric ciphers like ARIA‎. ‎W‎e examine (0,1)‎-‎diffusion layers and prove a theorem about them‎. ‎At last‎, ‎we study linearized MDS diffusion layers of symmetric ciphers Loiss, SMS4 and ZUC‎, from the mathematical viewpoint

Statistical Properties of Multiplication mod 2n2^n

In this paper, we investigate some statistical properties of multiplication mod $2^n$ for cryptographic use. For this purpose, we introduce a family of T-functions similar to modular multiplication, which we call M-functions as vectorial Boolean functions. At first, we determine the joint probability distribution of arbitrary number of the output of an M-function component bits. Then, we obtain the probability distribution of the component Boolean functions of combination of a linear transformation with an M-function. After that, using a new measure for computing the imbalance of maps, we show that the restriction of the output of an M-function to its upper bits is asymptotically balanced

Efficient MDS Diffusion Layers Through Decomposition of Matrices

Diffusion layers are critical components of symmetric ciphers. MDS matrices are diffusion layers of maximal branch number which have been used in various symmetric ciphers. In this article, we examine decomposition of cyclic matrices from mathematical viewpoint and based on that, we present new cyclic MDS matrices. From the aspect of implementation, the proposed matrices have lower implementation costs both in software and hardware, compared to what is presented in cryptographic literature, up to our knowledge