PRINCE Cipher and eFUSE-Based Embedded Encryption System for Optical Nerve Stimulator

The use of miniaturized wireless biomedical devices is expanding rapidly. Despite their limited size, power, processing, and storage capabilities, these devices must maintain a minimum level of security to protect against constantly evolving threats. This work presents a 16-bit on-chip embedded encryption system for secure data communication and authentication in an implanted optical nerve stimulator, utilizing eFUSE, PRINCE cipher, hash functions, and error detection code. The foundry-provided eFUSE silicon intellectual property (IP) is modified to accommodate different operating modes and further mitigates the supply voltage drop problem during sensing that causes premature resetting. We also propose an area-constrained resource-sharing-based ASIC implementation of the PRINCE cipher architecture without modifying the arithmetic results of the encryption-decryption process. The area and power consumption of the PRINCE cipher are reduced by$2.7\times $and$5.1\times $, respectively, due to modification while maintaining a substantial cipher strength. The proposed cipher performed at par with the existing ASIC implementations of the PRINCE cipher in throughput and area-based form factor. The entire encryption block and the optical nerve stimulator were fabricated in$0.18~\mu $m BCDlite process, and measurement results showed correct encrypted bidirectional data transmission and stimulation when powered by wirelessly transferred power. The developed encrypted implant performed well in comparison to wirelessly powered neural stimulators (implants) and secured wirelessly powered Internet of Things (IoT) architectures.