Balanced Even-Variable Rotation Symmetric Boolean Functions with Optimal Algebraic Immunity, Maximum Algebraic Degree and Higher Nonlinearity

Rotation symmetric Boolean functions are good candidates for stream ciphers because they have such advantages as simple structure, high operational speed and low implement cost. Recently, Mesnager et al. proposed for the first time an efficient method to construct balanced rotation symmetric Boolean functions with optimal algebraic immunity and good nonlinearity for an arbitrary even number of variables. However, the algebraic degree of their constructed n-variable (n > 4) function is always less than the maximum value n -1. In this paper, by modifying the support of Boolean functions from Mesnager et al.'s construction, we present two new constructions of balanced even-variable rotation symmetric Boolean functions with optimal algebraic immunity as well as higher algebraic degree and nonlinearity. The algebraic degree of Boolean functions in the first construction reaches the maximum value n - 1 if n/2 is odd and n/2 &NOTEQUexpressionL; (2k + 1)(2) or (2k + 1)(2) + 2 for integer k, while that of the second construction reaches the maximum value for all n. Moreover, the nonlinearities of Boolean functions in both two constructions are higher than that of Mesnager et al.'s construction.