Registers – Records – Conductive
Reexamination Certificate
2000-01-28
2003-07-08
Frech, Karl D. (Department: 2876)
Registers
Records
Conductive
C235S379000, C235S380000
Reexamination Certificate
active
06588672
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor device resistant to forgery and falsification. More particularly, the invention relates to IC cards.
BACKGROUND OF THE INVENTION
An example of conventional art of producing IC cards resistant to forgery and falsification has been disclosed in “Processing of the 2nd workshop on Electronic Commerce” (Oakland Calif., Nov. 18-20, 1996).
To prevent IC cards from being forged and falsified, the above art stores a unique key code which works as a key in the chip of each IC card. This key code is used as an identification number of a user who is charged for a received service (such as telephone toll, gaming toll, and communication toll). For example, this number is corresponding to a credit-card number. The system offering the service (credit bureau or grantor) draws the charge from the bank account of the customer having the ID number. This key code can also be used for check credit information of the customer.
If a violator reads this important key code stored in memory area of the chip of each IC card, the IC card may be easily duplicated or forged. There are two ways of transferring data between an IC card and a read/write unit (RWU): contact type (making the IC card in contact with the RWU to transfer data) and non-contact type (using a radio technology to transfer data between the IC card and the RWU). Independently of these ways, each IC card contains a memory area and an I/O area through which data is transferred between the IC card and the RWU. This I/O area contains a processor circuit which can perform complicated encryption processing.
The key code stored in the memory area of the IC chip cannot be free from being analyzed and read electrically, physically, or chemically because the key code has been electrically stored in a memory cell in the memory area. In other words, as the memory cell is electrically charged (with electrons) to store a key code, it can be read in a visible form (as a pattern), for example, by an electronic microscope of high resolution. The key code in the memory cell may also be read by a fine machining unit when the memory area and its vicinity are machined until their conductors are exposed and the exposed memory and nearby circuits are driven electrically.
To prevent such illegal reading of the key code, the conventional art employs a battery to back up the operation of the IC card. With this, if any electrical, physical, or chemical attack is made on the IC chip and consequently the battery power is shut down, the content of memory is lost.
For example, using a sensor to detect a destructive attack onto the chip or its vicinity in the IC card with a backup battery, one can create such a circuit to erase the content of the memory in cooperation with the output of the sensor. A static RAM (SRAM) can then be used as a memory cell to assure deletion of the content of memory when the IC card is decomposed and the power is shut off.
Further, a conventional method for creating a code resistant to forgery and falsification has been disclosed in Japanese Non-examined Patent Publication No. 59-10937 (1984). To assure protection of the code against forgery and falsification, this method comprises measuring the resonance frequency and the amplitude and the phase deviation of the returned wave, converting these into a corresponding value according to an algorithm to make the measured values undisclosed, combining this value with a secret identification number into-a code, and storing the result.
This code number is permanently stored in the memory area of the IC chip.
The conventional art of protecting a code in respective IC cards against forgery and falsification requires a battery in each card. Provision of a battery in each IC card causes the following demerits: increase of production cost of IC-cards, the service life of the IC cards is limited by their battery lives, shock-sensitive cards (battery destruction or incomplete contact caused by shocks), and card thickness being limited by battery sizes.
Further, a conventional electrical method of creating a code, for example, a method of using characteristic dispersions of electric circuits, is not resistant enough to protect the code against forgery and falsification because the characteristic dispersion is very narrow, easily measured and duplicated, and the electric circuit is easily decomposed and decoded.
An object of the present invention is to provide an inexpensive and highly-reliable semiconductor device which is hard to be forged and falsified and a method of producing thereof.
SUMMARY OF THE INVENTION
The aforesaid object can be attained by giving one or more electrodes whose surfaces are rough (having irregular projections and dents) to both an IC chip and a card base, causing these electrodes to touch each other with the electrodes of the IC chip faced down, measuring the resistance of electrodes in connection, analog-to-digital converting the resistance, and using the result as the key code of the IC card.
The surfaces of electrodes easily change their roughness and resistance in connection when the electrodes in connection are separated. The electrodes cannot have the original resistances any more. Therefore, it is possible to check whether the IC card has been subject to a destructive attack.
Further, this object can be attained more effectively by giving one or more electrodes to both an IC chip and a card base, cementing these electrodes with an electroconductive adhesive material with the electrodes of the IC chip faced down, measuring the resistance of electrodes in connection, analog-to-digital converting the resistance, and using the result as the key code of the IC card.
This electroconductive adhesive material can make the contact resistance (which is an analog value) more unfixed and consequently make the contact resistance dispersion greater.
Furthermore, this object can be attained more effectively by giving one or more electrodes to both an IC chip and a card base, cementing these electrodes with an anisotropic electroconductive adhesive material containing fine conductive particles with the electrodes of the IC chip faced down, measuring the resistance of electrodes in connection, analog-to-digital converting the resistance, and using the result as the key code of the IC card.
Fine gold particles (5 &mgr;m to 10 &mgr;m in size) dispersed in the anisotropic electroconductive adhesive material can disperse the resistances between electrodes.
A greater effect in resistance dispersion can be obtained when the main ingredient of said electrodes is equal to that of the fine particles dispersed in the anisotropic electroconductive adhesive material.
This object can be attained by giving one or more electrodes whose surfaces are rough (having irregular projections and dents) to both an IC chip and a sheet, covering the IC chip with the sheet with their electrodes in contact, measuring the resistance of electrodes in connection, analog-to-digital converting the resistance, and using the result as the key code of the IC card.
In other words, this sheet coverage enables direct use of conventional processing of IC chips even when the IC cards are conventional faced-up cards, which can reduce the manufacturing cost of IC cards.
This object is attained more effectively by reading the A/D-converted code to the outside of the IC card, encrypting it, and writing the encrypted code back into the memory area in the IC chip of the IC card.
In other words, the IC card can be recognized as a certified IC card when an legally-converted code is written in the chip.
This object is attained more effectively by encrypting the A/D-converted code in the chip of the IC card, reading it to the outside of the IC card, encrypting it again, and writing the encrypted code back into the memory area in the IC chip of the IC card.
Namely, this encryption inside the chip can make the key code in the chip safer even when the data is read by a line monitor.
This object is attained more effectively by storing the key code of an IC card which was
Antonelli Terry Stout & Kraus LLP
Frech Karl D.
Hitachi , Ltd.
Sanders Allyson
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