Peer-to-Peer (P2P) service has gained a great popularity for content sharing among distributed users. Even if it brings a lot of attraction as a good content distribution method, security becomes a very critical issue because a service user needs to communicate with the other persons who could be untrustworthy. Traditional authentication mechanisms usually adopted public key mechanisms, and they are heavy and time consuming. Because of the randomness and mobility of mobile P2P service, the authentication should be lightweight and dynamic. In our work, we propose a mechanism based on visual cryptography and steganography for the mutual authentication between two users for P2P service, and for the P2P multicast service authentication. Our proposed authentication mechanism is lightweight and efficient because it is based on users’ vision by adopting visual cryptography and steganography, and most computation for image generation is only concentrated on authentication server.