Secure keypad scanning

A secure key scanning functionality drives the row lines and column lines of a key switch array with randomized pulses of different polarities, and drives signals in one direction from a row line through a pressed key and to a column line as well as in an opposite direction from the column line through the pressed key and to the row line. To make unauthorized detecting of key presses more difficult, row lines and column lines are driven with pulses that appear as actual key press conditions when in fact the pulses are dummy pulses and no corresponding key has been pressed. In one novel aspect, dummy pulses are generated so that the line being driven with the dummy pulses has the same sustained and consistent waveform as the intersecting row and column lines that have identical waveforms due to the actual key press.