Abstract: An authentication server provides a clue to a client indicating a random partial subset of a full pattern that characterizes a full digitized path on a frame of reference, and the client enters a data to fulfill an authentication factor suggested by the clue. The full pattern consists of an ordered set of data fields, which store parameters that specify the full digitized path on a reference grid for recognition. The server presents an instance of a graphical representation of the frame of reference, including an array of random indicators at data field coordinates in the frame of reference. The server accepts indicators from the array of indicators corresponding to coordinates along said digitized path identified by the random partial subset as input data to fulfill the authentication factor.