User authentication for devices with touch sensitive elements, such as touch sensitive display screens

Apparatus for authenticating a user, the apparatus comprising:

• a) at least one processor;
• b) a touch sensitive element for receiving finger touch information;
• and
• c) at least one storage device storing program instructions which, when executed by the at least one processor, perform a method including
• 1) receiving finger touch information via the touch sensitive element , the finger touch information including at least a time series of finger touch samples that define a trace of a signature, at least a portion of which includes a continuous touch gesture during which at least one fingertip is always in contact with the touch sensitive element,
• 2) determining a similarity between the time series of finger touch samples of the received finger touch information and stored finger touch information including a time series of finger touch samples previously provided by the user, and
• 3) authenticating, by the computer system, the user using at least the determined similarity by
• A) receiving the stored finger touch information previously provided by the user,
• B) determining a location of the apparatus,
• C) receiving a pass-fail threshold,
• D) adjusting the pass-fail threshold as a function of the determined location of the apparatus,
• E) determining whether the similarity is above the adjusted pass-fail threshold;
• and
• F) responsive to a determination that the similarity is above the adjusted pass-fail threshold, authenticating the user, and otherwise, responsive to a determination that the similarly is not above the adjusted pass-fail threshold, not authenticating the user.