Protecting smart cards from power analysis with detachable power supplies

• US 6,507,913 B1
• Filed: 12/30/1999
• Issued: 01/14/2003
• Est. Priority Date: 12/30/1999
• Status: Expired due to Term

• Current Assignee: Yeda Research and Development Co. Ltd. (Weizmann Institute of Science)
• Original Assignee: Yeda Research and Development Co. Ltd. (Weizmann Institute of Science)
• Inventors: Shamir, Adi
• Primary Examiner(s): Heckler, Thomas M.
• Application Number:
  US09/475,921
• Time in Patent Office: 1,111 Days
• Field of Search: 713/182-185, 713/189, 713/194, 713/210, 713/300, 713/310
• US Class Current: 726/36
• CPC Class Codes: G06F 2207/7219 Countermeasures against side channel or fault attacks
• CPC Class Codes: G06K 19/073 Special arrangements for circuits, e.g. for protecting identification code in memory protection against unauthorised use of computer memory G06F12/14

Abstract

A method and apparatus for protecting smart cards against simple and differential power attacks when they are inserted into card readers controlled by other entities. The technique is particularly useful in financial applications such as ATM cards, credit cards, and electronic wallets, in which cards have to be inserted into card readers which may be specifically manufactured or modified to perform undetectable measurements of the power supplied to the card during its normal operation. The basic technique is to use two capacitors embedded in the smart card in such a way that at any given time one of them is charged by the external power supply and the other one is discharged by powering the smart card chip. The roles of the two capacitors alternate rapidly, and the power supply is detached from the smart card chip in the sense that external power measurements do not reveal information about its internal operations.

Claims

1. A method of protecting a smart card including a smart card chip which performs computation from cryptanalytic attacks based on power analysis, in which during at least part of computation being performed, furnishing power to the smart card chip from a discharging capacitor contained in the smart card, and during some different part of the computation being performed, charging the capacitor from an external power supply.

2. The method of claim 1 in which the smart card chip is not directly connected to the external power supply at any time during computation.

3. The method of claim 1 in which the smart card chip is not directly connected to the external power supply when it processes secret data.

4. The method of claim 1 in which the smart card chip is not directly connected to the external power supply when it performs cryptographic computations.

5. The method of claim 1 in which the smart card contains one capacitor, which is alternately connected to the smart card chip and to the external power supply.

6. The method of claim 5 in which the smart card chip operates during those times it is connected to the capacitor, and halts during those times in which the capacitor is connected to the external power supply.

7. The method of claim 1 in which the smart card contains at least two capacitors, which are connected in such a way that at any given time one of the at least two capacitors is connected to the smart card chip and another of the at least two capacitors is connected to the external power supply.

8. The method of claim 7 in which the connections of the two capacitors are repeatedly reversed, and the smart card chip operates continuously.

9. The method of claim 7 in which the connections of the two capacitors are repeatedly reversed in a periodic way, and the smart card chip operates continuously.

10. The method of claim 1, in which the smart card contains at least three capacitors, which are connected in such a way that at any given time at least one of the at least three capacitors is connected to the smart card chip and at least one of the other at least three capacitors is connected to the external power supply.

11. A method comprising the steps of:

a) powering a smart card including a chip for performing computations by a discharging capacitor connected to the chip while it is performing at least part of its computations,

b) changing the connections to the capacitor to disconnect it from the chip and enable its charging, and

c) charging the capacitor while it is disconnected from the chip.

12. The method of claim 11, in which the change of connection is triggered by the voltage across the capacitor exceeding or dropping below a certain threshold.

13. The method of claim 11, in which the change of connection is triggered by counting a number of clock cycles.

14. The method of claim 11, in which the change of connection is triggered by the voltage across the capacitor exceeding or dropping below a certain threshold at the beginning of a clock cycle.

15. The method of claim 11, in which additional circuitry on the smart card discharges the capacitor to a fixed voltage before connecting it to the external power supply as part of the switchover process.

16. Apparatus comprising:

a) a smart card containing a smart card chip for performing calculations,

b) a capacitor,

c) contacts for connecting an external power supply to the capacitor, and

d) switchover logic for alternately connecting the capacitor to power the smart card chip and to be charged by the external power supply.

17. Apparatus according to claim 16 wherein the smart card chip is not directly connected to the external power supply at any time during computation.

18. Apparatus according to claim 16 wherein the smart card chip is not directly connected to the external power supply when it processes secret data.

19. Apparatus according to claim 16 wherein the smart card chip is not directly connected to the external power supply when it performs cryptographic computations.

20. Apparatus according to claim 16 wherein the smart card contains one capacitor, which is alternately connected to the smart card chip and to the external power supply.

21. Apparatus according to claim 16 wherein the smart card contains at least two capacitors, which are connected in such a way that at any given time one of the at least two capacitors is connected to the smart card chip and another of the at least two capacitors is connected to the external power supply.

22. Apparatus according to claim 21 wherein the switchover logic is such that the connections of the two capacitors are repeatedly reversed, and the smart card chip operates continuously.

23. Apparatus according to claim 16 wherein the switchover logic is such that the change of connection is triggered by the voltage across the capacitor exceeding or dropping below a certain threshold.

24. Apparatus according to claim 16 wherein the switchover logic is such that the change of connection is triggered by counting a number of clock cycles.

25. Apparatus according to claim 16 wherein the switchover logic is such that the smart card discharges the capacitor to a fixed voltage before connecting it to the external power supply as part of the switchover process.

26. Apparatus according to claim 16 wherein the switchover logic is such that the change of connection is triggered by the voltage across the capacitor exceeding or dropping below a certain threshold at the beginning of a clock cycle.

27. Apparatus according to claim 16 wherein the smart card contains at least three capacitors, which are connected in such a way that at any given time one of the at least three capacitors is connected to the smart card chip and another of the at least three capacitors is connected to the external power supply.