Towards Quantum Resilient IoT: A Backward-Compatible Approach to Secure BLE Key Exchange Against Quantum Threats

There's a significant move towards the adoption of Post-Quantum Cryptography (PQC). While there have been initiatives to transition conventional TCP/IP-based networks to PQC, Quantum Resilient Internet of Things (IoT) networks have not been as widely discussed. Presently, Bluetooth Low Energy (BLE) employs the Elliptic Curve Diffie-Hellman algorithm for Secure Connection (SC) pairing, which is vulnerable to quantum threats. In this study, we introduce a backward-compatible Post-Quantum Key Exchange (PQKE) protocol for BLE, utilizing the Kyber-512 algorithm that has been adopted by the National Institute of Standards and Technology as a post quantum Key Encapsulation Mechanism. Although Kyber-512 is quantum resilient, it has large key pairs and ciphertexts, which presents critical challenges for the limited computational resources of IoT devices. Our performance assessment reveals that with an Attribute Protocol Maximum Transmission Unit (ATT MTU) of 65 bytes, the pairing time increases by approximately 9 folds using our PQKE in comparison to the traditional BLE SC pairing, mainly due to increased data transmission. Nevertheless, by employing a larger ATT MTU, the pairing time of our PQKE mechanism can be minimized to be of the same order of magnitude as current pre-quantum key exchange for BLE. We therefore advocate for the adoption of larger ATT MTU sizes in quantum resilient BLE pairing to ensure the performance and usability of the technology in a post-quantum world.