The present invention relates to an unauthorized access prevention method for an integrated circuit.
In recent years, products using a semiconductor integrated circuit such as information tags, IC cards, credit cards, and prepaid cards have been introduced into the market, and are gradually expanding their share in the market. Such information tags and cards are often referred to as “smart cards” in general, and are said to be more counterfeit-resistant than magnetic stripe cards. It is however a fact that keywords or logic circuit structures within the cards are analyzed to cause unending damages of forgery, tampering, and impersonation. Countermeasures that have been administered against such damages in order to enhance safety of the smart cards include increasing data widths and complicating logics. However, all those countermeasures are significantly high in cost, so that there are naturally limitations in the smart card market under strong pressure for lower prices. (For further details, see Japanese Patent Application Laid-Open No. H07-110876.)
Further, cryptographic techniques high in secrecy, application of which are not limited to the smart cards, require a system that adopts such a key as to have a key length exceeding 128 bits and includes a large-scale microprocessor, being expected to become further larger-scale and complicated in the future. Details on the techniques are described in “Studies on implementation method for encryption algorithm and risk analysis thereon” (issued on Feb. 28, 2003 by Information-technology Promotion Agency/Information-technology SEcurity Center).
The present invention is to solve the conventional problem in that integrated circuits highly resistant to forgery, impersonation, and unauthorized accesses are complicated and expensive. The present invention therefore has an object to provide an unauthorized access prevention method implemented by a simple structure manufactured with ease and at low cost.
Therefore, according to the present invention, there is provided an unauthorized access prevention method for an integrated circuit including one or plural resistor elements capable of selecting between a high impedance state and a low impedance state irreversibly in an interface portion within the integrated circuit or a peripheral circuit portion,
in which, when a signal inconsistent with verification information and standard that are preset in the integrated circuit is received at least once, the impedance state of the resistor element is changed from an initial state to stop a part or all of accesses to the integrated circuit irreversibly.
According to the present invention, it becomes possible to structure an integrated circuit highly resistant to forgery, impersonation, and unauthorized accesses with a simple method.
Further, a highly safe IC card can be realized.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.
The present invention relates to an unauthorized access prevention method for an integrated circuit including one or plural resistor elements capable of selecting between a high impedance state and a low impedance state irreversibly in an interface portion within the integrated circuit or a peripheral circuit portion, in which, when a signal inconsistent with verification information and standard that are preset in the integrated circuit is received at least once, the impedance state of the resistor element is changed from an initial state to stop a part or all of accesses to the integrated circuit irreversibly.
It is preferable that the resistor element contain an organic conductor.
It is preferable that the resistor element be formed of a capacitor.
It is preferable that a voltage higher than at normal operation be applied to the resistor element in order to change its impedance.
It is preferable that a current larger than at normal operation be applied to the resistor element in order to change its impedance.
It is preferable that the verification information and standard that are preset in the integrated circuit contain a keyword or a logic.
It is preferable that the verification information and standard that are preset in the integrated circuit contain a clock frequency different from that in a specification.
It is preferable that the verification information and standard that are preset in the integrated circuit contain a power supply voltage different from that in a specification.
It is preferable that the integrated circuit contain an organic semiconductor.
An IC card which uses the above-mentioned unauthorized access prevention method is also preferable.
The present invention is characterized by including one or plural resistor elements capable of selecting between a high impedance state and a low impedance state irreversibly in an interface portion within the integrated circuit or a peripheral circuit portion, in which, when a signal inconsistent with verification information and standard that are preset in the integrated circuit is received at least once, the impedance state of the resistor element is changed from an initial state to stop a part or all of accesses to the integrated circuit irreversibly. The interface portion is a circuit portion for inputting/outputting a signal to/from the integrated circuit. Also, the peripheral circuit portion is a circuit portion other than a memory array and a microprocessor core. According to the present invention, the resistor element is in the high impedance state or the low impedance state. That is, there are two states with a high resistance and a low resistance, either of which is the initial state and can be changed. The signal inconsistent with the verification information and standard that are preset in the integrated circuit is selected from a keyword, a logic, a power supply voltage, a drive frequency (clock frequency), etc. If one of those is inputted intentionally, it is judged that an unauthorized access is performed with malicious intent (for example, for the purpose of stealing a drive condition, a keyword, or the like using chip analysis).
The resistor element may contain an organic conductor.
The resistor element may be formed of a capacitor.
A voltage or current larger than at normal operation may be applied to the resistor element in order to change its impedance.
The verification information and standard that are preset in the integrated circuit may contain a keyword, a logic, a clock frequency different from that in a specification, or a power supply voltage different from that in the specification.
The integrated circuit may be formed of an organic semiconductor.
According to the above methods, it is hardly possible to analyze the integrated circuit by an unauthorized access, and thus the safety of the circuit is enhanced. As a result, an inexpensive, highly safe IC card or the like can be realized by using one of the unauthorized access prevention methods described above.
Hereinafter, description will be made of embodiments of the present invention with reference to the drawings.
Description is first made of an integrated circuit and an unauthorized access prevention method according to one of the embodiments shown in
The power supply voltage of
As the fuse element of
Assuming that an unauthorized access has been attempted, when Tr1 is turned to the OFF state and Tr2 is turned to the ON state, the state of the fuse element becomes the high impedance state where the access is unacceptable.
The power supply voltage of
In this embodiment, an element used as the anti-fuse element has a structure in which a silicon oxide film with high resistance is sandwiched between gold thin films (capacitor structure).
The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore to apprise the public of the scope of the present invention, the following claims are made.
Number | Date | Country | Kind |
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2003-094813 | Mar 2003 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP04/04341 | 3/26/2004 | WO | 6/8/2005 |