Semi-bent Functions Research Articles

On semi-bent functions with Niho exponents

Semi-bent functions are a kind of Boolean functions with high nonlinearity. They have important applications in cryptography and communications. In this paper, two classes of semi-bent functions with Niho exponents are proposed. It is shown that all semi-bent functions of the first class attain the maximum algebraic degree, and there exists one subclass of semi-bent functions with maximum algebraic degree in the second class. Furthermore, two examples of semi-bent functions in a small field are given by using the zeros of some Kloosterman sums. Based on the result given by Kim et al., two examples of infinite families of semi-bent functions are also obtained. These results provide more available Boolean functions with high nonlinearity and high algebraic degrees for designing the filter generators of stream ciphers.

The Construction of Orthogonal Variable Spreading Factor Codes from Semi-Bent Functions

In a recent paper spreading codes for CDMA systems were constructed based on Hadamard matrices and semi-bent functions. These codes were applicable to synchronous CDMA systems and to quasi-synchronous CDMA systems when a loosely-synchronized code is used. The codes consist of the union of rows of four Hadamard matrices. The codes can be assigned to a regular tessellation of hexagonal cells in such a way that the correlation between codewords assigned to adjacent cells is zero, while the correlation between codewords assigned to non-adjacent cells is small. The use of codewords from four Hadamard matrices allows greater codeword re-use distances than the use of codewords from a single Hadamard matrix. This has advantages for both satellite and terrestrial systems. These codes only support a single data rate. The current paper shows how orthogonal variable spreading factor codes can be created from them by a careful selection of the semi-bent functions used.

Semibent Functions From Dillon and Niho Exponents, Kloosterman Sums, and Dickson Polynomials

Kloosterman sums have recently become the focus of much research, most notably due to their applications in cryptography and coding theory. In this paper, we extensively investigate the link between the semibentness property of functions in univariate forms obtained via Dillon and Niho functions and Kloosterman sums. In particular, we show that zeros and the value four of binary Kloosterman sums give rise to semibent functions in even dimension with maximum degree. Moreover, we study the semibentness property of functions in polynomial forms with multiple trace terms and exhibit criteria involving Dickson polynomials.

Geometric and design-theoretic aspects of semibent functions II

This article is the successor of Dempwolff and Neumann (Des. Codes Cryptogr. 57:373---381, 2010). We now consider semibent functions with a linear structure. Semibent functions of partial spread type with a linear structure seem to be rare. We distinguish four classes of such semibent functions. For three classes we exhibit some examples.

On Balanced Semi-Bent Functions with High Algebraic Degrees

A class of balanced semi-bent functions with an even number of variables is proposed. It is shown that they include one subclass of semi-bent functions with maximum algebraic degrees. Furthermore, an example of semi-bent functions in a small field is given by using the zeros of some Kloosterman sums. Based on the result given by S. Kim et al., an example of infinite families of semi-bent functions is also obtained.

The Lower Bounds on the Second Order Nonlinearity of Bent Functions and Semi-bent Functions

该文研究了形如f(x,y)的n+1变元bent函数和半bent函数的二阶非线性度，其中xGF(2n), yGF(2)。首先给出了f(x,y)的2n-1个导数非线性度的精确值；然后推导出了函数f(x,y)的其余2n个导数的非线性度紧下界。进而给出了f(x,y)的二阶非线性度的紧下界。通过比较可知所得下界要优于现有的一般结论。结果表明f(x,y)具有较高的二阶非线性度，可以抵抗二次函数逼近和仿射逼近攻击。

Construction of semi-bent functions with high algebraic degrees

A class of semi-bent functions with an even number of variables is constructed by using the values of Kloosterman sums. These semi-bent functions are Boolean functions with four trace terms. Moreover, it is shown that the algebraic degrees of the new semi-bent functions attain the maximum values.

Geometric and design-theoretic aspects of semibent functions I

Geometric and design-theoretic aspects of semibent functions I

A New Characterization of Semi-bent and Bent Functions on Finite Fields*

We present a new characterization of semi-bent and bent quadratic functions on finite fields. First, we determine when a GF(2)-linear combination of Gold functions Tr(x2i+1) is semi-bent over GF(2n), n odd, by a polynomial GCD computation. By analyzing this GCD condition, we provide simpler characterizations of semi-bent functions. For example, we deduce that all linear combinations of Gold functions give rise to semi-bent functions over GF(2p) when p belongs to a certain class of primes. Second, we generalize our results to fields GF(pn) where p is an odd prime and n is odd. In that case, we can determine whether a GF(p)-linear combination of Gold functions Tr(xpi+1) is (generalized) semi-bent or bent by a polynomial GCD computation. Similar to the binary case, simple characterizations of these p-ary semi-bent and bent functions are provided.

On Bent and Semi-Bent Quadratic Boolean Functions

The maximum-length sequences, also called m-sequences, have received a lot of attention since the late 1960s. In terms of linear-feedback shift register (LFSR) synthesis they are usually generated by certain power polynomials over a finite field and in addition are characterized by a low cross correlation and high nonlinearity. We say that such a sequence is generated by a semi-bent function. Some new families of such function, represented by f(x)=/spl Sigma//sub i=1//sup (n-1)/2/c/sub i/Tr(x(2/sup i/)+1), n odd and c/sub i//spl isin/F/sub 2/, have recently (2002) been introduced by Khoo et al. We first generalize their results to even n. We further investigate the conditions on the choice of c/sub i/ for explicit definitions of new infinite families having three and four trace terms. Also, a class of nonpermutation polynomials whose composition with a quadratic function yields again a quadratic semi-bent function is specified. The treatment of semi-bent functions is then presented in a much wider framework. We show how bent and semi-bent functions are interlinked, that is, the concatenation of two suitably chosen semi-bent functions will yield a bent function and vice versa. Finally, this approach is generalized so that the construction of both bent and semi-bent functions of any degree in certain range for any n/spl ges/7 is presented, n being the number of input variables.

Fast evaluation, weights and nonlinearity of rotation-symmetric functions

We study the nonlinearity and the weight of the rotation-symmetric ( RotS) functions defined by Pieprzyk and Qu. We give exact results for the nonlinearity and weight of 2-degree RotS functions with the help of the semi-bent functions and we give the generating function for the weight of the 3-degree RotS function. Based on the numerical examples and our observations we state a conjecture on the nonlinearity and weight of the 3-degree RotS function.