On the degree, nonlinearity, algebraic thickness, and nonnormality of Boolean functions, with developments on symmetric functions

The two main criteria evaluating, from cryptographic viewpoint, the complexity of Boolean functions are the nonlinearity and the algebraic degree. Two other criteria can also be considered: the algebraic thickness and the nonnormality. Simple proofs are given that, asymptotically, almost all Boolean functions have high algebraic thicknesses and are deeply nonnormal, as well as they have high algebraic degrees and high nonlinearities. We also study in detail the relationship between nonnormality and nonlinearity. We derive simple proofs of known results on symmetric Boolean functions and we prove several new and more general results on a class containing all symmetric functions.