Image Number 3 for United States Patent #4479112.
A secure keyboard input terminal is disclosed in which a secret user identification code number or other confidential data sequence formed from a set of alpha-numeric characters (for example, the ten numerical digits 0 through 9) may be input secretly by a user, the terminal itself comprising (a) a plurality of input keys (in the case of one illustrated apparatus, 10 separate keys), (b) a corresponding plurality of character displays adapted for displaying said characters and (c) electronic circuitry for (1) apparently randomly associating selected ones of said character set to respective individual keys, (2) displaying to the user the character thus associated with each key and (3) translating a signal representing the actuation of a particular key by the user into a signal representing the particular character then associated with that key. In one illustrated embodiment the individual keys are buttons provided with opaque walls surrounding a transparent central bore through which a seven segment numerical display character may be viewed, but only by a person located directly above the keyboard. In one alternative embodiment, the individual key areas have a central bore portion and push button key adjacent to the central bore portion and in other embodiments visual security is maintained by the use of a set of transparent plates with opaque coatings or thin plates between the adjacent plates. One embodiment reassociates the displayed digits prior to the input of a data sequence in response to the manual actuation of a START key and retains the same scrambled association of digits to keys during the successive actuation of keys thus associated with the data sequence to the input. Other embodiments permit the user to manually initiate an automatic random (or apparently random) reassociation between the displayed digits (or other characters) and the individual keys at any time during the inputting of a data sequence or automatically reassociate characters and keys each time an individual data character (or predetermined number of characters) is input. Different types of random or apparently random sequence generating techniques may be employed. A host system processes the output code and accomplishes the desired function following validation.