CodeHop: physical layer error correction and encryption with LDPC-based code hopping

Abstract

This paper proposes a novel scheme named CodeHop, which provides both information reliability and security using code hop ping based on low-density parity-check (LDPC) codes. In contrast to traditional systems that perform error correction and encryption at different layers, CodeHop combines these two operations into a single step at physical layer, such that each plaintext message is jointly encoded and encrypted by a hopping parity-check matrix. According to a pseudo-random number generator (PRNG), the hopping matrix may rapidly switch among a sequence of LDPC parity-check matrices, which is randomly generated by a structured-random protograph expanding technique. Simulations show that reliable communication can be achieved by CodeHop with good error-correcting performance. In the meantime, CodeHop may improve the security of traditional systems such as GSM. Taking the A5/1 stream cipher used in GSM as the PRNG, it is shown that CodeHop is resistant to existing chosen-plaintext attacks that break A5/1 cipher already. Moreover, the security of CodeHop will be enhanced in the presence of channel errors as well.