A Physical Encryption Scheme for Low-Power Wireless M2M Devices: a Dynamic Key Approach

Physical Layer Security (PLS) has emerged as a promising solution for small and resource-limited wireless communications devices, to reduce the overhead associated with the required security resources and latency. In contrast to traditional security schemes, PLS relies on and benefits from the random nature of physical channels. However, the majority of PLS schemes in the literature lack the notion of secrecy and dynamicity, and employ static keys to generate fixed cipher primitives. In this paper, a dynamic key generation scheme that combines a pre-shared/stored secret key with a dynamic nonce extracted from channel information (for each new session) is proposed. The main advantage of this approach is that it achieves a high-security level with minimal overhead. Moreover, the obtained dynamic key can be changed frequently upon any change in channel parameters. Using the produced dynamic keys, cipher primitives are generated (permutation operations), which get updated for each frame symbol. This process ensures different and unique encryption layers for each new input frame and for each symbol in the input frame. Equally important, the proposed encryption algorithm operates at the modulation symbol level in order to attain performance by limiting the effect of error propagation and by realizing parallel encryption/decryption for each frame symbol. In addition, a preamble encryption scheme is also proposed to prevent unauthorized synchronization or channel estimation by illegitimate users. The security level of the proposed cipher scheme mainly depends on a secret key and the dynamicity of the channel to update the cipher primitives used for each frame symbol. Finally, security and performance analyses validate the efficiency and the robustness of the proposed approach.