SUMMARYThe risk of an illegal attack against the sensor devices used by the sensor network has been recently reported. Therefore, it is important that a security countermeasure by using an encryption technique. Then, lightweight block ciphers, which can realize low power, small area, and low latency, have been attracted attention as security countermeasures. Midori is a lightweight block cipher designed for the low power. Regarding the hardware security, the threat of fault analysis for a cryptographic circuit is pointed out. It is important that the tamper resistance verification of lightweight block ciphers against the fault analysis for the security of the future sensor devices. However, the fault analysis for lightweight block ciphers has barely been studied. Therefore, this study proposes a new fault analysis method for Midori. The proposed method performs the statistical analysis for the estimation of the key. Moreover, the proposed method performs two stages statistical fault analysis to analyze the all secret keys of Midori. Simulation results demonstrated the validity of the proposed method and the vulnerability of Midori against the proposed method.