  Next-generation personalized healthcare devices are undergoing extreme
miniaturization in order to improve user acceptability. However, such
developments make it difficult to incorporate cryptographic primitives using
available target technologies since these algorithms are notorious for their
energy consumption. Besides, strengthening these schemes against side-channel
attacks further adds to the device overheads. Therefore, viable alternatives
among emerging technologies are being sought. In this work, we investigate the
possibility of using memristors for implementing lightweight encryption. We
propose a 40-nm RRAM-based GIFT-cipher implementation using a 1T1R
configuration with promising results; it exhibits roughly half the energy
consumption of a CMOS-only implementation. More importantly, its non-volatile
and reconfigurable substitution boxes offer an energy-efficient protection
mechanism against side-channel attacks. The complete cipher takes 0.0034 mm$^2$
of area, and encrypting a 128-bit block consumes a mere 242 pJ.
