Cryptography – Cryptanalysis
Patent
1995-09-20
1999-06-29
Cangialosi, Salvatore
Cryptography
Cryptanalysis
380 2, 380 25, H04L 900
Patent
active
059179090
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a system for testing the authenticity of a data carrier.
A system of this type is known e.g. from EP-A1 0 313 967. From this publication it is known to selectively influence the physical fine structure of the IC during chip production and thus incorporate certain structures on or in the integrated circuit that are evaluatable as a physical property characterizing the circuit. In this connection this publication proposes providing the chip with a metallic coating having a random surface structure which is scannable via a resistance measurement at several places, the obtained resistance profile being stored in the form of characteristic data for determining the authenticity of the data carrier. External access to the characteristics storage is no longer possible after burning out of a fuse, e.g. after the initialization phase.
The above system has the disadvantage, however, that the resistance profile is not only elaborate in terms of measurement technology and difficult to determine but is sometimes even unclear, thereby impairing the reliability of the test procedure. Furthermore, the known method cannot ascertain faulty burnings, whereby the fuse was not brought properly from the electroconductive to the nonconductive state, or subsequent manipulation of a properly burned out fuse, both of which would permit unauthorized access to the characteristics storage.
The affect of the invention is to propose a system for testing the authenticity of data carriers which permits more reliable determination of authenticity and better protection of sensitive areas of the data carrier, whereby the physical property determined by the integrated circuit should be detectable with little effort in terms of measurement technology.
This problem is solved according to the invention by the features stated in the claims.
The invention is characterized in that a separate circuit is provided on the integrated circuit of the data carrier, which the semiconductor maker realizes by slightly changing the design of the integrated circuit. The circuit has an irreversibly adjusted electric state characterizing the circuit which is used for establishing a characteristic value for the data carrier and evaluated for determining authenticity.
In a first embodiment the circuit of the integrated circuit includes at least one network consisting of passive components and can additionally contain a control logic for driving switching elements. In a preferred embodiment example this network is executed as a resistor string between an outer free contact connection, which serves as a measuring connection, and the ground connection of the data carrier. For coding this resistor string, which can consist of binomially constructed resistors, fuses are connected in parallel with each series-connected resistor, which are burned out according to the desired coding. Burning out of the fuses is possible only in the test mode, i.e. after the chip has been tested and found good. When the fuses are being burned out an accordingly high current is driven to ground from the free outer measuring connection, the control logic guaranteeing that only those fuses are burned out whose parallel-connected switches are open according to the desired coding. After coding of the resistor string a fuse located between the control logic and the switching elements and unrecognizable without special aids can be burned out to prevent the control logic from being operated in the test mode again. This guarantees that the coding of the network can only be done within the test mode by the semiconductor maker. The coding can for example yield a continuous number, i.e. an individual identification for the integrated circuit, or else be a class feature for the integrated circuit. The expert will of course recognize that the invention is not restricted to the realization of a resistor string, but that other passive components, for example capacitors or inductors, can also be used for the network characterizing the circuit.
Alternatively a test connection (test p
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Cangialosi Salvatore
GAO Gesellschaft fur Automation und Organisation mbH
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