Abstract: A transistor integrated circuit particularly for use in transaction cards such as credit cards or payment cards comprises conductive film zones on the surface of the circuit having a shape and layout which makes it difficult or impossible to determine the layout of the circuit. Additional metal zones may be formed at the level or below the level of the transistor connection strips, which cannot be eliminated without eliminating the strips. Alternatively, instead of strips, metal zones extended in two dimensions are used whereby their junction to an underlying transistor may not be easily located by observing their surface by microscopic means.

Abstract: In a transaction card such as a credit or payment card provided with an integrated circuit for performing and recording the transaction, communications between the card and an access terminal must be coded so as to prevent fraud attempts. An integrated circuit coding device for coding or decoding a message in accordance with a confidential coding key comprises active transistors, and passive transistors, i.e. permanently blocked and/or permanently conductive, interconnected in such a way that observation of such circuit by means of an electronic microscope does not allow the determination of the confidential key which is implemented by the circuit.