Another SPA Key Recovery Against Random Order Countermeasures for AES Key Expansion

摘要

To increase the resistance against power analysis, random order countermeasure applied to AES key expansion was proposed and evaluated by Clavier et al. in CHES 2014. The proposed column-wise random order countermeasure showed certain resistance when the power consumption of the key expansion part is used for key recovery. For further evaluation, Clavier et al. analyzed the improvement of key recovery attack using fault injection as additional information. As for the acceleration of the key recovery, this work argues that extracting power information of AES state is more preferred than performing fault injections for practical attackers. This work comprehensively evaluates the random order countermeasure assuming the attackers use the power consumptions of AES state to accelerate the key recovery. We studied the relationship between key recovery result and the amount of information from AES state via both theoretical analysis and key recovery simulations. The results (a) demonstrate a set of effective key extractions with no fault injections and (b) discover the most cost-effective attack is extracting Hamming weight of 12 bytes for 2 AES executions, whose key extraction averagely finishes in 1 min.