Physical layer phase encryption for combating the traffic analysis attack

Encryptions are used in almost all standards to ensure the confidentially of the data. Encryptions can be and indeed are implemented in the different layers of a network protocol stack. The conventional encryption performs the bitwise XOR operation between one message bit and one key stream bit to generate one ciphertext bit. Huo et. al. have recently proposed to provide confidentialities on the user data by performing the phase encryption on time domain OFDM samples in the LTE system. Phase encryptions are performed on the modulated symbols, different from the bit level of XOR encryption, i.e., stream cipher encryption. In this paper, we extend their work. We first generalize the phase encryption to any communication systems independent of the underlying modulation scheme. We then show the phase encryption at the physical layer can resist the traffic analysis attack, which cannot be prevented by any security primitives in the upper layers. Finally, we make the comparisons between the phase encryption and the XOR encryption when both performed at the physical layer in terms of efficiency and security.