A security device for the identification or authentication of valuable goods is described, including a thin material layer (22, 26) presenting a stochastic pattern including micro/submicrostructures, where the latter are arranged in blobs (2) each of which presents a complexity factor Cx = L 2 4 ⁢ π · A , where L is the perimeter of the blob and A its area, and wherein blobs having a Cx value greater than or equal to 2 cover at least 5%, preferably at least 15%, of the device surface. According to a preferred embodiment, the material layer may include a film including at least a first and a second polymers arranged respectively within a first and a second phases defining the micro/submicrostructures. Preferred processes of fabrication are also disclosed, as well as a method for securing a valuable good based on such a security device.