Protection of software programs stored in read-only memory from

Details Protection of software programs stored in read-only memory from Protection of software programs stored in read-only memory from

1995-04-28

1997-09-23

Cain, David C.

Cryptography

Cryptanalysis

380 25, 380 49, H04L 900

Patent

active

056712758

ABSTRACT:
In a microprocessor-based controller, scrambled program data words are stored in a read-only memory and user information is stored in a random-access memory. A data converter is connected in the data bus between the microprocessor and the memories for descrambling data words when the ROM is accessed to produce a replica of original program data words and applying the replica to the microprocessor for operating the controller. The data converter simply applies data words to the microprocessor without descrambling when the RAM is accessed. The scrambled program data words in the read-only memory may be divided into multiple data blocks, each of which is a scrambled form of the original program data words with each of multiple keywords defined respectively for the data blocks. A modulo-2 adder is provided for summing each of the keywords with the scrambled program data words of a corresponding data block.

REFERENCES:
patent: 4319079 (1982-03-01), Best
patent: 5065429 (1991-11-01), Lang
patent: 5224166 (1993-06-01), Hartmann, Jr.
patent: 5371792 (1994-12-01), Asai et al.
patent: 5416840 (1995-05-01), Cane et al.
patent: 5457746 (1995-10-01), Dolphin
patent: 5555304 (1996-09-01), Hasebe et al.

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