i²Key: A Cross-sensor Symmetric Key Generation System Using Inertial Measurements and Inaudible Sound

Networked devices, such as wearable devices, laptops, smart home appliances, etc., are ubiquitous nowadays. To secure communication among those devices, symmetric keys are widely used because of their feasibility in resource-constrained networked devices. The observations of sensors from independent devices have been adopted for symmetric key generation. The identical biometrics information or environment interference has been observed by sensors, and their corresponding patterns are used for key generation. Popular signals from networked devices are inertial measurements, sound, wireless signals, etc. The existing sensor-based key generation solutions use the same type of sensors for both devices. Different from the existing solutions, we are the first to propose a cross-sensor symmetric key generation system i² Key, where two devices collect inertial measurements from a motion sensor and inaudible sound from a microphone, respectively. A new coding framework is designed for general key generation. We also pro-pose an efficient and accurate time synchronisation method for key generation. Additionally, a multi-tier key reconciliation method is suggested to improve key generation performance. By using the proposed architecture, the key generation rate is improved by up to approximately 40% compared with the situation without using it. We also perform security analysis and randomness analysis over the proposed method.