We study the probability distributions of difference propagation probabilities and input-output correlations for functions and block ciphers of given dimensions, for several of them for the first time. We show that these parameters have distributions that are well-studied in the field of probability such as the normal, Poisson and extreme value distributions. The results of this paper can be used to estimate how much effort will be required to generate functions satisfying certain criteria. The distributions we derive for block ciphers illustrate the significant difference between fixed-key parameters and averaged parameters.