Patent ID: 6259435
Filing Date: 2001-07-10
Classification: G06F

Abstract:
In an input device including a key matrix having a number of activatable keys that, when activated, cause an interconnection between a corresponding one of a number of row signal lines and a corresponding one of a number of column signal lines, a method of obfuscating detection of activation of the keys, the method including:a first phase including the steps of,(a) during each of a plurality of first scan cycles, applying a signal to at least two associated ones of the row signal lines and simultaneously applying a duplicate signal to at least two randomly selected ones of the column signal lines,(b) scanning the column signal lines during each of the first scan cycles to detect a first signal on a detected one of the column signal lines not having the duplicate signal applied thereto upon a first detection one of the first scan cycles during which at least two associated candidate ones of the row signal lines have signals applied thereto, and(c) storing information indicative of said detected column signal line and said candidate row signal lines;a second phase including the steps of,(d) during each of a plurality of second scan cycles, applying a signal to at least two associated ones of the row signal lines and simultaneously applying a duplicate signal to a randomly selected one of the column signal lines other than said detected column signal line,(e) scanning the column signal lines during each of at least two shared row ones of the second scan cycles, wherein a corresponding common one of said candidate row signal lines has a signal applied thereto during each of said shared row scan cycles, to detect a second signal on said detected column signal line during a second detection one of said shared row scan cycles, and(f) determining a detected row signal line as a row signal line having a signal applied thereto during each of said first and second detection cycles.