Methods and apparatus for securely enabling features in highly i

Details Methods and apparatus for securely enabling features in highly i Methods and apparatus for securely enabling features in highly i

1992-05-13

1993-09-21

Swann, Tod R.

Cryptography

Particular algorithmic function encoding

Nbs/des algorithm

380 4, 380 25, 380 50, H04K 100

Patent

active

052475778

ABSTRACT:
Methods and apparatus for securely providing an encryption scheme for a highly integrated circuit arrangement using external function-enabling keys. Unencrypted question and encrypted expected answer values are stored in question and answer registers respectively. The encrypted expected answer value is derived from a suitably secure encryption scheme. An external key chip incorporating a coding block implementing the identical encryption scheme is provided for each optional feature to be enabled. The unencrypted question value is routed to the input of the coding block. The coding block returns an encrypted key answer value to a comparator in the circuit arrangement. The encrypted key answer value is compared to the encrypted expected answer value stored in the answer register and, if equivalent, the comparator signals the circuit arrangement that a match has been found and that the optional function is to be enabled. The unencrypted questions values together with the associated expected answer values may be randomized according to any suitable randomization scheme. Determination of the expected answer values to circumvent the security feature in commercially viable quantities is greatly reduced.

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Appendix A. Data Encryption Standard, Federal Information Processing Standards Publication Jan. 15, 1977.

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