In this paper, the authors review a comparison study on the most common used authentication methods. Some of these methods are actually based on cryptography. In this paper, they show the main cryptographic services. As well as, this paper presents a specific discussion about authentication service. Since the authentication service is classified into several categorizes according to their methods. However, this paper gives more about the real life example for each of the authentication methods. It talks about the simplest authentication methods as well about the available biometric authentication methods such as voice, iris, fingerprint, and face authentication.