Detection of the authenticity of an electronic circuit or of a product containing such a circuit

1. A non-transitory computer-readable medium having contents which cause a host device to perform a method, the method comprising:

initializing a charge retention circuit of a slave device, wherein initializing the charge retention circuit comprises switching off a power supply of the slave device;

receiving an indication of a discharge time of the charge retention circuit;

determining an authenticity of the slave device based on the received indication of the discharge time of the charge retention circuit; and

controlling communication with the slave device based on the determined authenticity of the slave device.

2. The non-transitory computer-readable medium of claim 1 wherein the method comprises comparing information representative of time, generated by the charge retention circuit, with information indicative of an expected duration.

3. The non-transitory computer-readable medium of claim 1 wherein a duration of time in which the power supply of the slave device is switched off is random.

4. The non-transitory computer-readable medium of claim 1 wherein the method comprises:

transmitting, to the slave device, a voltage representative of a charge level to be stored in the charge retention circuit;

charging of the charge retention circuit;

measuring a residual quantity of charge in the charge retention circuit at an expiration of a duration of time; and

comparing information indicative of the measured residual quantity of charge with an expected value of said information.

5. The non-transitory computer-readable medium of claim 1 wherein the method comprises:

transmitting, to the slave device, a value indicating to the slave device a no-response time-period;

initializing of a time counter and switching off of the power supply of the slave device;

switching on the power supply and periodically interrogating the slave device until the slave device responds to an interrogation;

determining an elapsed duration based on when the slave device responded to the interrogation; and

comparing the determined elapsed duration with an expected duration.

6. The non-transitory computer-readable medium of claim 1 wherein the method comprises:

encrypting communications with the slave device.

7. A method, comprising:

responding, by a slave device, to an initialization signal received via an interface by:

initializing a charge-retention circuit, wherein the initialization signal controls switching off of a power supply associated with the charge-retention circuit;

generating an indication of a discharge time of the charge-retention circuit; and

controlling communication with a host device via the interface based on the determined indication.

8. The method of claim 7 wherein the controlling communication with the host device comprises transmitting the indication to the host device via the interface.

9. The method of claim 7 wherein the initialization signal comprises a voltage representative of a charge level to be stored in the charge-retention circuit, and the method comprises:

charging the charge retention circuit;

measuring a residual quantity of charges in the charge-retention circuit at an expiration of a duration of time; and

transmitting, to the host device via the interface, information representative of the residual quantity.

10. The method of claim 7 wherein the initialization signal comprises a value indicative of a no-response time-period, and the method comprises responding to the initialization signal by:

charging the charge-retention circuit;

ignoring interrogations received via the interface until a charge-level of the charge-retention circuit corresponds to an expiration of the no-response time-period.

11. The method of claim 10 wherein the value indicative of the no-response period is encrypted.

12. The method of claim 7 comprising:

encrypting communications with the host device.

13. A non-transitory computer-readable medium having contents which cause a slave device to perform a method, the method comprising:

responding to an initialization signal received via an interface by:

initializing a charge-retention circuit, wherein the initialization signal controls switching off of a power supply associated with the charge-retention circuit;

generating an indication of a discharge time of the charge-retention circuit; and

controlling communication with a host device via the interface based on the determined indication.

14. The non-transitory computer-readable medium claim 13 wherein the controlling communication with the host device comprises transmitting the indication to the host device via the interface.

15. The non-transitory computer-readable medium of claim 13 wherein the initialization signal comprises a voltage representative of a charge level to be stored in the charge-retention circuit, and the method comprises:

charging the charge retention circuit;

measuring a residual quantity of charges in the charge-retention circuit at an expiration of a duration of time; and

transmitting, to the host device via the interface, information representative of the residual quantity.

16. The non-transitory computer-readable medium of claim 13 wherein the initialization signal comprises a value indicative of a no-response time-period, and the method comprises responding to the initialization signal by:

charging the charge-retention circuit;

ignoring interrogations received via the interface until a charge-level of the charge-retention circuit corresponds to an expiration of the no-response time-period.

17. The non-transitory computer-readable medium of claim 16 wherein the value indicative of the no-response period is encrypted.

18. The non-transitory computer-readable medium of claim 17 wherein the value indicative of the no-response period is received from a third device.

19. A device, comprising:

a charge-retention circuit having:

a floating node;

a first capacitor coupled between the floating node and a first reference-voltage terminal;

a second capacitor coupled between the floating node and a second reference-voltage terminal; and

a third capacitor coupled between the floating node and a third reference-voltage terminal, wherein the first, second and third capacitors have different charge retention capabilities;

a communication interface to couple to a host device; and

circuitry, which, in operation, responds to an initialization signal, by:

initializing the charge-retention circuit, wherein the initializing signal switches off of a power supply associated with the charge-retention circuit;

generating an indication of a discharge time of the charge-retention circuit; and

controlling communication with the host device based on the determined indication.

20. The device of claim 19 wherein,

a charge retention capability of the first capacitor is greater than a charge retention capacity of the second capacitor,

the charge retention capability of the first capacitor is greater than a charge retention capacity of the third capacitor, and

the charge retention capability of the second capacitor is greater than the charge retention capacity of the third capacitor.