Key Controlled Substitution for Cryptographic Applications
Original Publication Date: 1978-Mar-01
Included in the Prior Art Database: 2005-Feb-20
This article describes a substitution function designed for cryptographic systems in which n bits of input data are transformed into n bits of output data under cipher key control. Statistical roughness is the correlation between the input and output data, i.e. the smoother the statistics, the more random is the relation. Good cryptographic systems tend to smooth out the statistical roughness. If all possible inputs to the substitution function are transformed into different outputs, the substitution function is defined as nonsingular, whereas if two or more inputs are transformed into the same output, the substitution function is defined as singular. Nonsingular functions are preferred because they tend to distribute the bits more evenly, i.e., smooth out the statistics.