Cryptographic redundancy and mixing functions

Studies the application of structures based on error correcting codes to systems where the major requirement is not error control but secrecy. In many cases the same code can achieve both error control and secrecy. The first section of the paper describes an optimal construction for combining multiple semi-secure channels into a single channel with much higher security. Usually the security of a communications channel cannot be guaranteed, only promised with a high degree of probability. The first section shows how to combine semi-secure channels in such a way that predetermined number may compromised before information revealed. The maximum possible secure capacity of a set of semi-secure channels is just the sum of the capacities of those channels that are in fact secure. The author presents a theorem which states that this bound on total secure capacity is, in fact, achievable. The paper proceeds to show how mixing and scrambling functions formed from error correcting codes can be used to enhance the security of trunked communications circuits and conventional cryptographic systems which depend, for their security, on unproved assertions about computational difficulty. The last segment of the paper presents a concept for applying information theoretic security to spread spectrum communications and ranging systems so that even an intended recipient of the message will not be able to jam the signal