Secure wireless communications is a challenging problem due to the shared nature of the wireless medium. Most existing security mechanisms focus on traditional cryptographic schemes. In recent years, features of the multi-path channel (such as randomness and reciprocity), have driven researchers to exploit its potential to enhance the security of wireless networks. As OFDM occupies wide bandwidth, it will experience a prolific source of multi-path components. In this paper, we comprehensively exploit the inherent physical parameters of the multi-path fading channel to achieve continuous two way authentication between wireless terminals. In our scheme, pilot information is randomly spread in a wideband channel, leading to low probability of detection (LPD). Unlike other channel-based approaches, the information of both amplitude and phase in the channel signature is fully utilized to enhance the security of the OFDM communication network. More specially, the receiver will detect the channel response continuously according to the randomly inserted pilots and identify the valid user based on the statistical channel signature information. Simulation results indicate the high efficiency of the proposed method.