Protection of secret value using hardware instability

1. A method for data security, comprising:

providing an electronic circuit having a first, stable operating mode under a first operating condition and a second, unstable operating mode under a second operating condition, the second operating condition being different from the first operating condition, the electronic circuit being configured to output a correct secret value only in the first operating mode;

maintaining the electronic circuit initially in the second operating condition;

transferring the electronic circuit to the first operating condition and, while in the first operating condition, reading out the secret value; and

returning the electronic circuit to the second operating condition after reading out the secret value;

wherein, for given circuit operating conditions, the electronic circuit has a stable operating mode if an output value of a particular circuit characteristic is predictable and the electronic circuit has an unstable operating mode if the output value of the particular circuit characteristic is not predictable.

2. The method according to claim 1 ,

wherein the first operating condition corresponds to application of a first operating voltage to the electronic circuit and the second operating condition corresponds to application of a second operating voltage to the electronic circuit, the first operating voltage being different from the second operating voltage, and

wherein transferring the electronic circuit comprises switching from the second to the first operating voltage.

3. The method according to claim 1 ,

wherein the first operating condition corresponds to application of clock pulses at a first clock rate to the electronic circuit and the second operating condition corresponds to application of clock pulses at a second clock rate to the electronic circuit, the first clock rate being different from the second clock rate, and

wherein transferring the electronic circuit comprises switching from the second to the first clock rate.

4. The method according to claim 1 ,

wherein the first operating condition corresponds to a first operating temperature of the electronic circuit and the second operating condition corresponds to a second operating temperature of the electronic circuit, the first operating temperature being different from the second operating temperature, and

wherein transferring the electronic circuit comprises changing from the second to the first operating temperature.

5. The method according to claim 1 , wherein transferring the electronic circuit comprises receiving a control signal requesting the secret value, and switching momentarily from the second to the first operating condition in response to the control signal.

6. The method according to claim 1 , wherein the electronic circuit comprises a flip-flop, which is metastable in the second operating mode and stable in the first operating mode.

7. A data security device, comprising:

an electronic circuit having a first, stable operating mode under a first operating condition and a second, unstable operating mode under a second operating condition, the second operating condition being different from the first operating condition, the electronic circuit being configured to output a correct secret value only in the first operating mode; and

means for controlling the operating condition of the electronic circuit, so as to maintain the electronic circuit initially in the second operating condition, to transfer the electronic circuit to the first operating condition so as to cause the electronic circuit to output the secret value, and to return the electronic circuit to the second operating condition after the secret value has been output;

wherein, for given circuit operating conditions, the electronic circuit has a stable operating mode if an output value of a particular circuit characteristic is predictable and the electronic circuit has an unstable operating mode if the output value of the particular circuit characteristic is not predictable.

8. The device according to claim 7 ,

wherein the first operating condition corresponds to application of a first operating voltage to the electronic circuit and the second operating condition corresponds to application of a second operating voltage to the electronic circuit, the first operating voltage being different from the second operating voltage, and

wherein the means for controlling the operating condition comprise a power supply, which is configured to switch from the second to the first operating voltage.

9. The device according to claim 7 ,

wherein the first operating condition corresponds to application of clock pulses at a first clock rate to the electronic circuit and the second operating condition corresponds to application of clock pulses at a second clock rate to the electronic circuit, the first clock rate being different from the second clock rate, and

wherein the means for controlling the operating condition comprise a clock generator, which is configured to switch from the second to the first clock rate.

10. The device according to claim 7 ,

wherein the first operating condition corresponds to a first operating temperature of the electronic circuit and the second operating condition corresponds to a second operating temperature of the electronic circuit, the first operating temperature being different from the second operating temperature, and

wherein the means for controlling the operating condition comprise a temperature controller, which is configured to switch the electronic circuit from the second to the first operating temperature.

11. The device according to claim 7 , wherein the means for controlling the operating condition are configured to switch momentarily from the second to the first operating condition in response to a control signal requesting the secret value.

12. The device according to claim 7 , wherein the electronic circuit comprises a flip-flop, which is metastable in the second operating mode and stable in the first operating mode.

13. A data security device, comprising:

an electronic circuit having a first, stable operating mode under a first operating condition and a second, unstable operating mode under a second operating condition, the second operating condition being different from the first operating condition, the electronic circuit being configured to output a correct secret value only in the first operating mode; and

a controller configured to control the operating condition of the electronic circuit, so as to maintain the electronic circuit initially in the second operating condition, to transfer the electronic circuit to the first operating condition so as to cause the electronic circuit to output the secret value, and to return the electronic circuit to the second operating condition after the secret value has been output;

wherein, for given circuit operating conditions, the electronic circuit has a stable operating mode if an output value of a particular circuit characteristic is predictable and the electronic circuit has an unstable operating mode if the output value of the particular circuit characteristic is not predictable.

14. The device according to claim 13 ,

wherein the first operating condition corresponds to application of a first operating voltage to the electronic circuit and the second operating condition corresponds to application of a second operating voltage to the electronic circuit, the first operating voltage being different from the second operating voltage, and

wherein the controller comprises a power supply, which is configured to switch from the second to the first operating voltage.

15. The device according to claim 13 ,

wherein the first operating condition corresponds to application of clock pulses at a first clock rate to the electronic circuit and the second operating condition corresponds to application of clock pulses at a second clock rate to the electronic circuit, the first clock rate being different from the second clock rate, and

wherein the controller comprises a clock generator, which is configured to switch from the second to the first clock rate.

16. The device according to claim 13 ,

wherein the first operating condition corresponds to a first operating temperature of the electronic circuit and the second operating condition corresponds to a second operating temperature of the electronic circuit, the first operating temperature being different from the second operating temperature, and

wherein the controller comprises a temperature controller, which is configured to switch the electronic circuit from the second to the first operating temperature.

17. The device according to claim 13 , wherein the controller is configured to switch momentarily from the second to the first operating condition in response to a control signal requesting the secret value.

18. The device according to claim 13 , wherein the electronic circuit comprises a flip-flop, which is metastable in the second operating mode and stable in the first operating mode.