Tracking and prevention of fault injection attempt sequences using thermal memory
An integrated circuit (IC) includes a thermal memory device, a fault injection (FI) detector and a security control circuit. The thermal memory device includes (i) a thermal storage zone and (ii) a heating element configured to heat the thermal storage zone in response to write operations. The FI detector is configured to detect attempts to inject faults into the IC. The security control circuit is configured to perform a write operation to the thermal memory device in response to an attempt detected by the FI detector, to identify a sequence of the attempts that meets a density criterion, by reading the thermal memory device, and initiate a responsive action upon identifying the sequence.
1 . An integrated circuit (IC), comprising:
a thermal memory device comprising at least two thermal-storage bits, each thermal storage bit comprising a thermal storage device, a temperature measurement device, and a heating device configured to heat the thermal storage device in response to write operations;
a fault injection (FI) detector, configured to detect attempts to inject faults into the IC; and
a security control circuit, configured to:
perform a write operation to the thermal memory device in response to an attempt detected by the FI detector;
identify a sequence of the attempts that meets a density criterion, by reading the thermal memory device and detecting that at least a preset number of the thermal storage bits have been written; and
initiate a responsive action upon identifying the sequence.
2 . The IC according to claim 1 , wherein the thermal storage zone comprises one or more reference thermal storage bits that are not written.
3 . The IC according to claim 1 , wherein the temperature measurement device comprises a P-N diode.
4 . The IC according to claim 1 , wherein the thermal storage device comprises a thermally isolated metal layer.
5 . The IC according to claim 1 , wherein the security control circuit is configured to sequentially: (i) further to a power-up sequence, check for a failed-boot attempt indication in which a first thermal storage bit has been written and a second thermal storage bit has not been written; (ii) responsively to detecting the failed-boot attempt indication, abort the boot; (iii) write to the first thermal storage bit; and (iv) responsively to a successful boot sequence, write to the second thermal storage bit.
6 . The IC according to claim 1 , wherein the security control circuit is configured to identify the sequence of the attempts regardless of a reset event occurring in the IC during the sequence.
7 . A method for securing an integrated circuit (IC), the method comprising:
detecting attempts to inject faults into the IC;
in response to detecting an attempt to inject a fault, performing a write operation to a thermal memory device, which comprises at least two thermal-storage bits, each thermal storage bit comprising a thermal storage device, a temperature measurement device and a heating device configured to heat the thermal storage device in response to write operations;
identifying a sequence of the attempts that meets a density criterion, by reading the thermal memory device and detecting that at least a preset number of the thermal storage bits have been written; and
initiating a responsive action upon identifying the sequence.
8 . The method according to claim 7 , wherein the thermal storage zone comprises one or more reference thermal storage bits that are not written.
9 . The method according to claim 7 , wherein the temperature measurement device comprises a P-N diode.
10 . The method according to claim 7 , wherein the thermal storage device comprises a thermally isolated metal layer.
11 . The method according to claim 7 , further comprising, sequentially: (i) further to a power-up sequence, checking for a failed-boot attempt indication in which a first thermal storage bit has been written and a second thermal storage bit has not been written; (ii) responsively to detecting the failed-boot attempt indication, aborting the boot; (iii) writing to the first thermal storage bit; and (iv) responsively to a successful boot sequence, writing to the second thermal storage bit.
12 . The method according to claim 7 , wherein identifying the sequence of the attempts is performed regardless of a reset event occurring in the IC during the sequence.