An efficient and secure cipher scheme for MIMO–OFDM systems based on physical layer security

Multiple-input multiple-output orthogonal frequency division multiplexing (MIMO–OFDM) is, currently, the most dominant air interface for wireless communications, and the basic foundation for many network standards, due to its practicality and efficiency at high data speeds. Specifically, this system combines the MIMO and OFDM technologies, to achieve maximum capacity, reliability and throughput. On the other hand, achieving data confidentiality over wireless links in MIMO–OFDM systems, remains a pressing issue that should be tackled. In this paper, we propose an efficient and secure cipher scheme for MIMO–OFDM systems, based on the randomness and dynamicity of the physical layer. In particular, a channel-based parameter, which is extracted from the shared wireless channel, is combined with a secret key, only known to the communicating devices, to generate a dynamic key. This key is, then, used to derive two simple cipher primitives, which are a masking sequence and a permutation table. Both of these cipher primitives are updated frequently to enhance the security and robustness of transmitted data and prevent attacks. The proposed solution is considered very efficient and lightweight since it consists of simple operations, mainly, addition and permutation. Moreover, the proposed solution takes into consideration the OFDM frame symbol length, which can be fixed or varying from one antenna to another. Therefore, the proposed solution consists of two cipher variants, one secures OFDM symbols having the same length (same number of modulation symbols) and the other secures OFDM symbols that have different lengths on different antennas. Finally, several security and performance tests are conducted to prove the efficiency and robustness of the proposed solution.