Data entry keyboard apparatus
First Claim
1. A data entry keyboard apparatus, including an array of key switches connected between row and column conductors, and associated control means connected to said row and column conductors for detecting the actuation of a key switch and providing an output signal representing an actuated key switch, characterized in that said control means includes:
- random pattern generating means adapted to generate successive random patterns of first and second type binary signals;
a plurality of first port circuits coupled to said random pattern generating means and to respective ones of said row conductors;
a plurality of second port circuits coupled respectively to said column conductors;
decoding means coupled to said random pattern generating means and to said plurality of second port circuits;
and detection means coupled to said random pattern generating means and to said plurality of first port circuits, whereby each generated random pattern operates said decoding means to cause said second port circuits to provide a first type binary signal to a selected one of said column conductors and a second type binary signal to the remaining ones of said column conductors, and operates said plurality of first port circuits such that a row conductor, associated with an actuated key switch in the selected column, has a first type binary signal applied thereto and the remaining row conductors have binary signals applied thereto corresponding to the random pattern operating the decoding means, said detection means being further adapted to detect a first port circuit which has a second type binary signal applied thereto by the random pattern operating the decoding means and which is coupled to a row conductor having a first type binary signal applied thereto thereby enabling the generation of said output signal representing the actuated key switch.
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Accused Products
Abstract
A data entry keyboard apparatus includes a key switch array (18) in a keyboard unit (12) connected via a cable (14) to a tamper-resistant module (28) which contains control circuitry (16). The control circuitry (16) includes a random pattern generator (30) which generates successive random patterns, causing the selection of a single column and a random pattern of rows, thereby effecting the simulation of key actuations. An EXCLUSIVE-OR gating network (56a-56d) is effective to distinguish a genuine key actuation from simulated key actuations. The invention prevents the ascertainment of actuated keys by unauthorized tapping connections applied to the keyboard unit (12) or the cable (14).
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Citations
7 Claims
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1. A data entry keyboard apparatus, including an array of key switches connected between row and column conductors, and associated control means connected to said row and column conductors for detecting the actuation of a key switch and providing an output signal representing an actuated key switch, characterized in that said control means includes:
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random pattern generating means adapted to generate successive random patterns of first and second type binary signals; a plurality of first port circuits coupled to said random pattern generating means and to respective ones of said row conductors; a plurality of second port circuits coupled respectively to said column conductors; decoding means coupled to said random pattern generating means and to said plurality of second port circuits; and detection means coupled to said random pattern generating means and to said plurality of first port circuits, whereby each generated random pattern operates said decoding means to cause said second port circuits to provide a first type binary signal to a selected one of said column conductors and a second type binary signal to the remaining ones of said column conductors, and operates said plurality of first port circuits such that a row conductor, associated with an actuated key switch in the selected column, has a first type binary signal applied thereto and the remaining row conductors have binary signals applied thereto corresponding to the random pattern operating the decoding means, said detection means being further adapted to detect a first port circuit which has a second type binary signal applied thereto by the random pattern operating the decoding means and which is coupled to a row conductor having a first type binary signal applied thereto thereby enabling the generation of said output signal representing the actuated key switch. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification