What Is Single-Factor Authentication

What is single-factor authentication?

A) the traditional security process, which requires a user name and password
B) requires the user to provide two means of authentication, what the user knows (password) and what the user has (security token)
C) requires more than two means of authentication such as what the user knows (password) , what the user has (security token) , and what the user is (biometric verification)
D) the identification of a user based on a physical characteristic such as a fingerprint, iris, face, voice or handwriting