Electric power conversion systems – Current conversion – With voltage multiplication means
Reexamination Certificate
2000-05-26
2001-11-20
Patel, Rajnikant B. (Department: 2838)
Electric power conversion systems
Current conversion
With voltage multiplication means
C307S085000
Reexamination Certificate
active
06320770
ABSTRACT:
TECHNICAL FIELD
The invention relates to a data processing device, notably a chip card, which includes an integrated circuit and a power supply as disclosed in the introductory part of Claim
1
. The invention also relates to a method for powering an integrated circuit, notably in a chip card, as disclosed in the introductory part of Claim
6
.
STATE OF THE ART
In many data processing apparatus provided with an integrated circuit, for example, cryptographic operations are carried out so as to protect the operation of such apparatus or the data transported in the apparatus. The arithmetic operations required for this purpose are carried out by standard processors as well as by dedicated crypto processors. A typical example of the latter processor is formed by a chip card or IC card. Data or intermediate results used in this context customarily constitute security-relevant information such as, for example, cryptographic keys or operands.
The arithmetic operations performed by the integrated circuit, for example in order to calculate cryptographic algorithms, involve the formation of logic combinations of operands or intermediate results. Depending on the technology used, such operations, notably the loading of empty or previously erased storage sections or registers with data, lead to an increased current consumption of the data processing apparatus. In the case of complementary logic, for example CMOS, an increase of the current consumption occurs when the value of a bit storage cell changes, i.e. when its value changes from “0” to “1” or from “1” to “0”. The increase of the consumption is then dependent on the number of bit positions changed in the memory or register. In other words, the loading of a previously erased register causes an increase of the current consumption which is proportional to the Hamming weight of the operand (=number of bits having the value “1”) written into the empty register. Analysis of this current variation could thus enable extraction of information concerning the operations executed, thus enabling successful crypto analysis of secret operands such as, for example, cryptographic keys. When several current measurements are performed on the data processing apparatus, adequate information could be extracted, for example in the case of very small signal variations. On the other hand, a plurality of current measurements could also enable a possibly required differentiation. This type of crypto analysis is also called “Differential Power Analysis” whereby an outsider could successfully perform a possibly unauthorized crypto analysis of the cryptographic operations, algorithms, operands or data purely by observing changes in the current consumption of the data processing apparatus. “Differential Power Analysis” thus enables the extraction of additional internal information of an integrated circuit beyond pure functionality.
From U.S. Pat. No. 5,297,201 it is known to combine a high frequency radiating computer with a device which also irradiates a high frequency similar to that of the computer. Consequently, an unauthorized third party can no longer decode the high-frequency radiated by the computer. However, this system cannot prevent crypto analysis by a third party having direct access to the computer.
WO 90/15489 describes a protected communication system in which dummy traffic or dummy transfers take place so as to obstruct cryptographic analysis. However, this system cannot prevent crypto analysis by a third party having direct access to the computer either.
IMPLEMENTATION OF THE INVENTION, OBJECT, SOLUTION, ADVANTAGES
It is an object of the present invention to provide an improved data processing device and an improved method of the kind set forth which eliminate the described drawbacks and offer effective protection against “Differential Power Analysis”.
This object is achieved by means of a data processing device of the kind set forth which is characterized as disclosed in Claim
1
.
To this end, the power supply according to the invention includes a voltage converter which converts an input voltage V
ein
into a pulsed output voltage V
aus
so as to conduct it to the integrated circuit, where V
aus
<V
ein
.
This offers the advantage that all characteristic information concerning the operations carried out by the integrated circuit is eliminated from the variation in time of the current and the voltage, so that a resultant input current for the integrated circuit can no longer be used as a source of information for differential power analysis.
Preferred further embodiments of the data processing device are described in the Claims
2
to
5
.
The voltage converter in a preferred embodiment includes a switch and a control circuit for the switch, the switch being connected to ground via a capacitance and connecting, under the control of the control circuit, the capacitance alternately to the input voltage V
ein
and to the integrated circuit.
Furthermore, there is preferably provided a current-carrying supply lead with an input node which is connected to the input voltage V
ein
and an output node which outputs the output voltage V
aus
to the integrated circuit. The switch is arranged in such a manner that it interrupts the supply lead between the input node and the output node and connects, in a first position, the first capacitance to the input node via a first supply lead segment and, in a second position, to the output node via a second supply lead segment.
Preferably, the voltage converter includes an input capacitance which connects the supply lead between the input node and the first position of the switch to ground as well as an output capacitance which connects the supply lead between the second position of the switch and the output node to ground.
According to a method of the kind set forth according to the invention the supply current for the integrated circuit is converted in such a manner that on the external input only a pulsed current of constant pulse amplitude can be measured. To this end, an input voltage V
ein
is converted into a pulse width modulated output voltage V
aus
which is applied to the integrated circuit.
This offers the advantage that all characteristic information concerning the operations carried out by the integrated circuit is eliminated from the variation in time of the current and the voltage, so that a resultant input current for the integrated circuit can no longer be used as a source of information for differential power analysis.
REFERENCES:
patent: 4742291 (1988-05-01), Bobier et al.
patent: 4864292 (1989-09-01), Nieuwkoop
patent: 5206495 (1993-04-01), Kreft
patent: 5297201 (1994-03-01), Dunlavy
patent: 5426616 (1995-06-01), Kajigaya et al.
patent: 5438505 (1995-08-01), Cohen
patent: 5491623 (1996-02-01), Jansen
patent: 9015489A1 (1990-12-01), None
Patel Rajnikant B.
Piotrowski Daniel J.
U.S. Philips Corporation
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