Multilevel security with restricted character set translation

Naval message traffic is transmitted with restricted character set and optional files compression. Both character translation and data compression can be used for add-on data encryption. The authors present the restricted character set translation algorithms. The algorithms have been implemented with multilevel security access control using a master key scheme and have been incorporated in a data compression program for military applications. The restricted character set has been used to avoid hardware changes needed to expand the transmittable character set. Software can be used to expand the restricted character set without the need to buy expensive hardware