Sibciphers - symmetric iterative block ciphers with with functional keys

Abstract

A class of symmetric iterative block ciphers called SIBCiphers is defined. Each round of a cipher in this class is represented by an injective system of Boolean functions each depending on a small number of arguments being some inputs to the round. Round key in it includes some of these functions and (or) their actual arguments. The ciphertext bitstring is obtained by permuting the bits on the outputs of the last round. Contemporary symmetric block ciphers with additive round keys belong to this class. Two other subclasses of SIBCiphers are described. They are called by names Lucifer and Feistel and constructed according to the known cryptographic schemes originally suggested by H. Feistel and implemented in ciphers LUCIFER and DES respectively. Some synthesis problems for SIBCiphers are discussed.