A comparative analysis of VLSI trusted virtual sensors

This paper analyzes three cryptographic modules suitable for digital designs of trusted virtual sensors into integrated circuits, using 90-nm CMOS technology. One of them, based on the keyed-hash message authentication code (HMAC) standard employing a PHOTON-80/20/16 lightweight hash function, ensures integrity and authentication of the virtual measurement. The other two, based on CAESAR (the Competition for Authenticated Encryption: Security, Applicability, and Robustness) third-round candidates AEGIS-128 and ASCON-128, ensure also confidentiality. The cryptographic key required is not stored in the sensor but recovered in a configuration operation mode from non-sensitive data stored in the non-volatile memory of the sensor and from the start-up values of the sensor SRAM acting as a Physical Unclonable Function (PUF), thus ensuring that the sensor is not counterfeit. The start-up values of the SRAM are also employed in the configuration operation mode to generate the seed of the nonces that make sensor outputs different and, hence, resistant to replay attacks. The configuration operation mode is slower if using CAESAR candidates because the cryptographic key and nonce have 128 bits instead of the 60 bits of the key and 32 bits of the nonce in HMAC. Configuration takes 416.8 µ s working at 50 MHz using HMAC and 426.2 µ s using CAESAR candidates. In the other side, the trusted sensing mode is much faster with CAESAR candidates with similar power consumption. Trusted sensing takes 212.62 µ s at 50 MHz using HMAC, 0.72 µ s using ASCON, and 0.42 µ s using AEGIS. AEGIS allows the fastest trusted measurements at the cost of more silicon area, 4.4 times more area than HMAC and 5.4 times more than ASCON. ASCON allows fast measurements with the smallest area occupation. The module implementing ASCON occupies 0.026 mm2 in a 90-nm CMOS technology.