A system for duplicating a master key includes a mechanism for receiving and positioning a master key. The master key defines a major key axis and an intermediate key axis along which a key blade variably extends, and a minor key axis along a key thickness. Optical path components direct a light beam along the minor key axis. The light beam impinges upon the key blade. A portion of the light beam traverses the key blade. A detector receives the portion of the light beam that traverses the key blade. An apparatus imparts relative motion along the major key axis between the light beam and the master key. The light beam scans along the major key axis of the master key. A processor receives a signal from the detector as the beam scans along the major key axis and generates information usable for defining the machining of a duplicate key.