Cryptographic redundancy and mixing functions

This paper studies the use of structures based on error correcting codes to achieve secrecy rather than error control. In many cases, however, the same code can achieve both error control and secrecy. It describes an optimal construction for combining multiple semisecure channels, e.g., a bundle of fiber-optic cables or reels of tape sent by independent couriers, into a single channel with much higher security. It shows 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 unproven assertions about computational difficulty.