  Mathematically-secure cryptographic algorithms leak significant side channel
information through their power supplies when implemented on a physical
platform. These side channel leakages can be exploited by an attacker to
extract the secret key of an embedded device. The existing state-of-the-art
countermeasures mainly focus on the power balancing, gate-level masking, or
signal-to-noise (SNR) reduction using noise injection and signature
attenuation, all of which suffer either from the limitations of high power/area
overheads, performance degradation or are not synthesizable. In this article,
we propose a generic low-overhead digital-friendly power SCA countermeasure
utilizing physical Time-Varying Transfer Functions (TVTF) by randomly shuffling
distributed switched capacitors to significantly obfuscate the traces in the
time domain. System-level simulation results of the TVTF-AES implemented in
TSMC 65nm CMOS technology show > 4000x MTD improvement over the unprotected
implementation with nearly 1.25x power and 1.2x area overheads, and without any
performance degradation.
