Computer-aided design and analysis of circuits and semiconductor – Nanotechnology related integrated circuit design
Reexamination Certificate
1999-03-10
2001-12-25
Everhart, Caridad (Department: 2825)
Computer-aided design and analysis of circuits and semiconductor
Nanotechnology related integrated circuit design
Reexamination Certificate
active
06334206
ABSTRACT:
The invention relates to a microcontroller circuit comprising circuit elements arranged on a semiconductor body.
The reliability of microcontroller circuits, notably for identification systems such as bank credit cards, security systems and the like, is becoming increasingly more important. For example, cash is being replaced more and more by bank credit cards. In respect of use such credit cards should have properties comparable to those of cash. This has a direct effect on the requirements imposed as regards the protection against decryption and forgery of such cards and the microcontroller circuits used thereon.
Because of their construction and their field of application, microcontroller circuits have the property that they can be copied as often as desired and that they can offer functions or data an unlimited number of times. Exactly these properties are in contradiction with the basic property of cash. Therefore, special steps are required so as to enable the use of microcontroller circuits in bank credit cards as a substitute for cash or as a tool for cash-like transactions, without failing to meet the required security level.
There are essentially two categories of attempted forgery of a microcontroller circuit used in a credit card. The first category concerns attempts aimed at the data connection and the data exchange between the microcontroller and the environment, i.e. apparatus in operative contact with the credit card. This category of forgery is counteracted by data encryption methods to ensure the confidentiality and authenticity of the data exchanged.
A second category of attempted forgery of microcontroller circuits in credit cards concerns the attempted decryption and manipulation of the data stored in the microcontroller circuit, for example money units. These attempts may be very diverse. The course of action is dependent on physical and topographic properties of the microcontroller circuit used.
Microcontroller circuits for the described applications nowadays are constructed so as to have an as modular as possible topographic configuration. The topography of the circuit elements of individual function blocks is conceived such that perfect operation is achieved with a minimum use of surface area on the semiconductor body. The overall microcontroller circuit is formed in a modular fashion from function blocks thus developed for different functions. This facilitates and accelerates the development of such microcontroller circuits, but it also facilitates the recognizability and discovery of the assignment of the circuit elements and function blocks to the individual functions to be executed by the microcontroller circuit or to the data stored therein.
Therefore, it may occur that during forgery it is attempted to discover the individual functions of the microcontroller circuit by optical analysis (using a microscope) of the topography. The difficulty then is the least in the case of regular, typical structures in the topography. For example, on the basis of the knowledge of the fact that a microcontroller circuit utilizes a data bus having a word width of
8
bits it may be possible to identify a regular pattern of conductors with eight parallel conductors as a data bus. Such identification makes it easier to monitor or manipulate data on such a data bus.
It is an object of the invention to provide a microcontroller circuit of the kind set forth in which attempted forgery as described above is made at least substantially more difficult.
In a microcontroller circuit of the kind set forth this object is achieved according to the invention by means of an irregularly scrambled spatial configuration of at least a number of co-operating circuit elements on the semiconductor body. Such a configuration makes the regularity of modular structures and function blocks of such a microcontroller circuit irrecognizable to such an extent that analysis of and assignment of the individual circuit elements to given functions or data of the microcontroller require a significantly increased amount of equipment and time. This not only substantially reduces the probability of success of such an analysis, but the cost of such attempted forgery is increased disproportionally in comparison with the benefits to be derived, so that the threshold against forgery is significantly raised. The irregular configuration on the microcontroller circuit may concern the shape and appearance of the individual circuit elements. However, preferably the positions of at least a number of co-operating circuit elements on the semiconductor body and/or the location and routing of the connection leads connected thereto are irregularly scrambled. Use can be made of the fact that circuit elements which are intended for different functions within the microcontroller circuit in most cases have an at least substantially similar construction. This occurs already in the sense of a simple, reliable construction, i.e. in the sense of a modular construction in conventional microcontroller circuits. Therefore, for at least some of the circuit elements of the microcontroller the assignment of a circuit element to a given function of the microcontroller can be determined only by the position of the circuit element on the semiconductor body and, if desired or additionally, by the location and routing of connection leads connected to the relevant circuit element. For example, when irregular scrambling is then performed, resulting in the elimination of regular, modular structures on the semiconductor body, it is no longer possible to discover the function of the circuit elements on the basis of these structures alone. Circuit elements which neighbor one another in the topography of the microcontroller circuit now no longer exhibit the operational coherence known from regular, modular topographies. For example, the individual elements of a shift register chain which spatially adjoin one another in the conventional modular construction can be arranged in positions which are irregularly distributed across the surface of the semiconductor body, or the topography of the shift register structure can be blurred by irregularly routing the connection leads.
If only the location and routing of the connection leads are scrambled in the topography of the microcontroller circuit on a semiconductor body, but the positions of the individual circuit elements are left the same whereas their function within the microcontroller circuit is at least partly scrambled in conformity with the scrambling of the connection leads, only comparatively few additional manufacturing steps or devices will be required so as to manufacture microcontroller circuits having the same function but a completely different appearance. In that case it is in principle only necessary to modify wiring masks for the different topographies, whereas the diffusion masks may remain the same.
Further scrambling and hence camouflaging of the topography can be achieved by assigning given circuit elements their function within the microcontroller circuit only by data which can be variably stored in given other circuit elements of the microcontroller circuit. This enables further scrambling yet even in the case of identical external topography.
In a further embodiment of the microcontroller circuit according to the invention, comprising a central processor unit, at least a number of the circuit elements included in the central processor unit is irregularly scrambled in respect of position and/or location and routing of connection leads connected thereto. This is in contrast with circuit elements included in storage units in the microcontroller circuit for which preferably only the location and routing of connection leads are irregularly scrambled, i.e. at least for a number of the circuit elements of said storage units. This embodiment of the invention takes into account the fact that realizing an irregular construction of storage elements is very difficult from a technical point of view. With a view to achieving an acceptable cost of manufacture of the microcontroller circui
Everhart Caridad
Piotrowski Daniel J.
Siek Vuthe
U.S. Philips Corporation
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