The present invention increases the difficulty of interpreting
electromagnetic emissions from a keypad system by facilitating randomness
in the electromagnetic emissions associated with a particular key
activation. A keypad security circuit utilizes a set of digital values
that varies over both time and the bits as a keypad driver word applied
to a keypad attribute (e.g., a row or column). The keypad security system
of the present invention drives the varying strong keypad driver signal
to an attribute of a keypad switch matrix (e.g., the rows or columns),
applies an independently configured weak driver signals to the opposing
attribute of the keypad switch matrix, retrieves a resulting signal from
the opposing attribute, and interprets the results to determine if a
switch included in a keypad system was activated (e.g., a key is
pressed).