Secret-key-controlled reversible circuit and corresponding method of data processing

Abstract

A combinatorial key-dependent network suitable for the encryption/decryption of data on buses and in memories of data-processing devices, has a number of layers, where each layer has a number of elementary building blocks operating on very small block sizes. A generic building block acts on a small number of input data bits, which are divided into two groups of m and n bits, respectively. The m input bits, which are passed to the output intact, are used to select k out of 2k key bits by a multiplexer circuit; the k bits are then used to select an (n×n)-bit reversible transformation acting on the remaining n input bits to produce the corresponding n output bits. The total number of the key bits in the building block is thus 2k, which can easily he made larger that m+n. An inverse building block is the same except that the reversible transformations are replaced by their inverses.