Construction of Rotation Symmetric Boolean Functions on Odd Number of Variables with Maximum Algebraic Immunity

In this paper we present a theoretical construction of Rotation Symmetric Boolean Functions (RSBFs) on odd number of variables with maximum possible algebraic immunity (AI) and further these functions are not symmetric. Our RSBFs are of better nonlinearity than the existing theoretical constructions with maximum possible AI. To get very good nonlinearity, which is important for practical cryptographic design, we generalize our construction to a construction cum search technique in the RSBF class. We find 7, 9, 11 variable RSBFs with maximum possible AI having nonlinearities 56, 240, 984 respectively with very small amount of search after our basic construction.