Patent ID: 7757083

Claim:
A method comprising generating authentication information for a first device from a group of devices that exhibit variation between devices due to fabrication variations, the method comprising: selecting one or more configurations of a plurality of circuit components of the device according to selection information provided to the device, the one or more configurations being selected from among a plurality of selectable configurations of the components, wherein each selected configuration of circuit components is associated with one or more signal paths through said components; for each selected configuration, forming the one or more signal paths associated with said configuration through components configured according to the selected configuration, and propagating a signal through each of the formed signal paths, each of said signal paths having a dynamic characteristic associated with the propagation of the signal that is unique in the group to that device; determining authentication information that is specific to the device based on the dynamic characteristics of the formed signal paths, wherein matching authentication information can be regenerated by repeating the forming of the signal paths through the component, and propagating of the signals through the formed signal paths; wherein the dynamic characteristic of a signal path includes a delay characteristic of the signal path and wherein determining the authentication information includes determining said information based on the delay characteristics of the formed signal paths.