Data processing method and device

1. A data processing method implemented in an electronic apparatus for securing a microcircuit card against fault generation attacks comprising the following steps performed by a microprocessor of the microcircuit card during a same execution of a computer program by the microprocessor:

verifying a criterion indicative of normal running of the method to detect a fault generation attack on the microcircuit card;

updating an error flag when the verifying step result is negative, thereby detecting a fault generation attack on the microcircuit card;

testing the error flag; and

a processing executed when the step of testing the error flag indicates the verifying step result is negative and a fault generation attack is detected on the microcircuit card,

wherein the processing step is separated from the verifying step by an intermediate step of non-null duration performed prior to testing the error flag,

wherein a first action is performed when the verifying step result is positive and prior to testing the error flag, wherein the intermediate step includes performing at least one second action having a same first external signature observable by an observer external to the microcircuit card as the first action,

wherein a third action is performed after testing the error flag when the verifying step result is positive and wherein the processing step includes performing at least one fourth action having a same second external signature observable by the observer external to the microcircuit card as the third action,

wherein said third and fourth actions comprise writing data in a physical memory and wherein said fourth action comprises the writing of at least one of:

blocking data preventing any subsequent use of the electronic apparatus, and

data representative of a detected anomaly when the verifying step result is negative, said data representative of the detected anomaly enabling an analysis of a problem encountered by said electronic apparatus,

wherein the same first external signature is a same electrical consumption signature or a same electromagnetic radiation signature of the electronic apparatus generated by the first action and by the second action and the same second external signature is a same electrical consumption signature or a same electromagnetic radiation signature of the electronic apparatus generated by the third action and by the fourth action.

2. The data processing method of claim 1 , wherein the second action is performed at a time the first action would be performed when the verifying step result is positive.

3. The data processing method of claim 1 , wherein the second action is different from the first action.

4. The data processing method of claim 1 , wherein a number of instructions used in the first action and in the second action is the same.

5. The data processing method of claim 1 , wherein the type of instruction used by the first action and by the second action is the same.

6. The data processing method of claim 1 , wherein the first action includes accessing a first area of said physical memory and wherein the second action includes accessing a second area of said physical memory different from the first area.

7. The data processing method of claim 1 , wherein said physical memory is a rewritable semiconductor memory.

8. The data processing method of claim 7 , wherein said physical memory is in an external device.

9. The data processing method of claim 8 , wherein the external device is a user terminal.

10. The data processing method of claim 1 , wherein the first action is performed in a secure step.

11. The data processing method of claim 10 , wherein the secure step includes a cryptographic algorithm.

12. The data processing method of claim 1 , wherein the criterion is negative if an anomaly is detected.

13. The data processing method of claim 1 , wherein the criterion is negative if an attack is detected.

14. The data processing method of claim 1 , wherein the criterion is negative if a functional error is detected.

15. The data processing method of claim 1 , implemented by a microprocessor of a microcircuit card.

16. The data processing method of claim 1 , wherein the fourth action is performed at a time the third action would be performed when the verification is positive.

17. The data processing method of claim 1 , wherein a number of instructions used in the third action and in the fourth action is the same.

18. The data processing method of claim 1 , wherein a type of instruction used by the third action and by the fourth action is the same.

19. The data processing method of claim 1 , wherein the third action includes accessing a third area of a said physical memory and wherein the fourth action includes accessing a fourth area of said physical memory different from the third area.

20. A data processing device comprising:

a microcircuit card with a microprocessor;

the microprocessor having the following means that are operative during a same execution of a computer program by the microprocessor,

means for verification of a criterion indicative of normal operation of the device to detect a fault generation attack on the microcircuit card;

means for updating an error flag when the verification is negative, thereby detecting a fault generation attack on the microcircuit card;

means for testing the error flag;

processing means activated when the means for testing the error flag indicates that the verification is negative and a fault generation attack is detected on the microcircuit card; and

separation means for separating the operation of the verification means from the operation of the processing means with an intermediate step of a non-null duration performed prior to testing the error flag,

wherein the microprocessor is configured to perform a first action prior to testing the error flag when the means for verification indicates a positive result, and wherein said separation means is configured to perform a second action having a same external signature observable by an observer external to the microcircuit card as the first action,

wherein the microprocessor is configured to perform a third action after testing the error flag when the means for verification indicates the positive result, and wherein the processing means is configured to perform a fourth action having a same second external signature observable by the observer external to the microcircuit card as the third action,

wherein said third and fourth actions write data in a physical memory and wherein said fourth action writes at least one of:

blocking data preventing any subsequent use of the device, and

data representative of a detected anomaly when the verification is negative, said data representative of the detected anomaly enabling an analysis of a problem encountered by said device,

wherein the same first external signature is a same electrical consumption signature or a same electromagnetic radiation signature of the device generated by the first action and by the second action and the same second external signature is a same electrical consumption signature or a same electromagnetic radiation signature of the device generated by the third action and by the fourth action.