Abstract: Addressing the problem that the artificial noise method can be cracked by the eavesdropper with multiple antennas in wireless communication systems, a sufficient condition is proposed for secure physical layer transmission with finite alphabet inputs. Under this guideline, a signal-like artificial noise method is designed to ensure the system security transmission. Analysis reveals that the equivalent channel between the finite alphabet input and the eavesdroppers noise-free output is a Discrete Noisy Lossless Channel (DNLC). Since the reversibility of the input under a DNLC provides the necessary condition for eavesdropping, the eavesdropper can augment its antennas to successfully squeeze out the secure information, nullifying the systems secrecy mutual information. As a result, destroying the reversibility of the input signal becomes a sufficient condition for the secure physical layer transmission with finite alphabet inputs. The signal-like artificial noise method satisfies the sufficient condition, which can ensure the secure physical layer transmission. Simulation results demonstrate the efficacy of this method.