Explanation:
Two-factor authentication requires more than one type of user authentication. While biometrics provides unique authentication, it is not strong by itself, unless a PIN or some other authentication factor is used with it. Biometric authentication by itself is also subject to replay attacks. A symmetric encryption method that uses the same secret key to encrypt and decrypt data is not a typical authentication mechanism for end users. This private key could still be compromised. SSL is the standard security technology for establishing an encrypted link between a web server and a browser. SSL is not an authentication mechanism. If SSL is used with a client certificate and a password, it would be a two-factor authentication.