SECURE MICROPROCESSOR

An apparatus and method is disclosed for the protection of computer programs through the use of the principles of conditional inversion and permutation. These security features are designed as part of the chip in a fashion to minimize the changes required to any existing microprocessor design and to be transparent to firmware execution. The programs are first encrypted by permutation which reorders the lines according to an allocated scheme and then conditionally inverted through a set of dual input exclusive OR gates. The reordering of lines in the permutator and the conditional inversion in the inverter are accomplished through the use of variables some of which are permanently prestored in the microprocessor and some of which are entered by the programmer.