Myriads of ultra-constrained 4-bit micro controllers (MCUs) are deployed in (mostly) legacy devices, some in security sensitive applications, such as remote access and control systems or all sort of sensors. Yet the feasibility and practicability of standardized cryptography on 4-bit MCUs has been mostly neglected. In this work we close this gap and provide, to the best of our knowledge, the first implementations of ECC and SHA-1, and the fastest implementation of AES on a 4-bit MCU. Though it is not the main focus of this paper, we have investigated the SCA resistance trade-offs for ECC by implementing a variety of countermeasures. We hope that our comprehensive, highly energy-efficient crypto library—that even outperforms all previously published implementations on low-power 8-bit MCUs—will give rise to a variety of security functionalities, previously thought to be too demanding for these ultra-constrained devices.

NRF (Natl Research Foundation, S’pore)