METHOD TO AUTHENTICATE AND ACCESSORY

An apparatus ( 100 ) used by a plurality of devices to authenticate an accessory ( 120 ) is configured to operate with a device ( 110 ) of the plurality of devices. The accessory ( 120 ) applies an authentication algorithm to a key and a challenge ( 130 ) received from the device ( 110 ) and generates a response ( 132 ) thereto. A challenge and response memory ( 114 ) stores a subset of a set of challenges ( 232 ) and pre-computed responses ( 230 ). The enabling circuit transmits a challenge ( 130 ) to the accessory ( 120 ) and receives a received response ( 132 ) therefrom. The enabling circuit ( 112 ) also compares the received response ( 132 ) to the stored response ( 230 ) corresponding to the stored challenge ( 232 ) sent to the accessory ( 120 ). The enabling circuit ( 112 ) is configured to generate a normal operation enabling signal that enables normal operation of the device when the received response ( 132 ) matches the stored response and is configured not to generate the normal operation enabling signal when the received response ( 132 ) does not match the stored response.