I. Introduction
Hardware security becomes more important than ever in the Internet of Things (IoT) era. The design turnaround time of security oriented devices is shortened before going to manufacturing, under the increasing demands of information devices for mobile communications, connected cars, wearable devices and so forth, all with the higher level of security. Hardware security is hindered in a latent problem at the design stage and may become apparent after the production. Cryptographic algorithms are mathematically secure while vulnerable to hardware attacks, once they are actualized with physical implementation. Side channel (SC) attacks [1] are well known, which an adversary uses to unexpectedly decipher the secret information stored in a cryptographic device. Ubiquitous data processing entities including IoT devices are exposed to the real threat of SC attacks. The security risk and its evaluation methods for those encryption devices have been reported in several studies [2]–[4].