Fundamental Study on Methods of Protecting Cryptographic Modules from IEMI Fault Injection Using Spread Spectrum Clocking

A threat of intentional electromagnetic interference (IEMI) fault injection has been reported to extract the secret key of cryptographic devices by superimposing electromagnetic (EM) waves on the clock supplied to the cryptographic module via power cable. Furthermore, a threat has been demonstrated to reduce the time cost required for secret key analysis by synchronizing the clock and EM waves and controlling the phase of EM waves. In response, this paper proposes a countermeasure involving the disruption of EM wave synchronization and phase control through dynamic phase variation of the clock in each cycle. In this paper, we specifically focus on the spread spectrum clocking (SSC), which is a technique to vary the phase of the clock. And we demonstrate that using SSC to the cryptographic module can make it more difficult to apply to synchronize to the clock and control the phase of CW, thereby increasing the time cost required for key analysis. We experimentally confirmed that a clock with 1.0% frequency modulation can increase the time cost required for secret key analysis by about 38 times using an evaluation board.