A method is provided for identifying use of a proprietary circuit layout. A representation of a layout of a circuit is input and the locations of a set of predetermined physical features of the circuit are identified. This set of locations is then compared with a previously generated characteristic pattern file, the characteristic pattern file comprising a representation of relative locations of a set of these predetermined physical features in the proprietary circuit layout. If the set of locations matches the relative locations of the characteristic pattern file, then an output is generated indicating that use of the proprietary circuit design has been found.