Common-mode Current Reduction by Applying Mode-conversion Suppression Technique to Power Delivery Network as Side-channel Attack Countermeasure

The common-mode current flowing through a power cable contains the secret information of a cryptographic module that allows an attacker to eavesdrop from a remote location. Mode conversion conveys secret information as side-channel information from the normal-mode noise to the common-mode current at the connector section where the imbalance factor between the power cable and the trace on a power delivery network (PDN) is discontinuous. This common-mode current is generated due to mode conversion and flows through a power cable as side-channel information. We apply the mode-conversion suppression technique at the discontinuity point on a PDN to reduce the common-mode current as a side-channel attack (SCA) countermeasure. We place a capacitor at the discontinuity point to suppress mode conversion by reducing normal-mode voltage. Therefore, the common-mode current in a power cable should enhance the SCA resistance of the cryptographic module. We experimentally confirmed that installing a capacitor at the discontinuity point of the imbalance factor on a PDN efficiently suppresses mode conversion and reduces the common-mode current to counter SCAs from outside the cryptographic module.