The primary difference between single-factor authentication (SFA) and two-factor authentication (2FA) lies in the number of authentication factors required to verify a user’s identity.

Single-Factor Authentication (SFA):

• SFA relies on just one type of authentication factor for identity verification.
• The most common example of SFA is using a username and password combination. The user is required to know a specific piece of information (the password) to gain access.
• While SFA is simple and easy to implement, it has some security limitations. If the password is weak or compromised, there is a higher risk of unauthorized access.

Two-Factor Authentication (2FA):

• 2FA requires the user to provide two different types of authentication factors to access a system or account.
• The two factors typically fall into three categories: something the user knows (knowledge), something the user has (possession), and something the user is (inherence). For example, a common implementation is combining a password (knowledge factor) with a one-time code sent to a mobile device (possession factor).
• 2FA provides an additional layer of security compared to SFA. Even if one factor is compromised (e.g., a password is stolen), the attacker would still need the second factor for access.
• Common forms of 2FA include SMS codes, authenticator apps, biometric scans, or hardware tokens.

In summary, the key distinction is that SFA relies on a single authentication factor, while 2FA uses two factors to enhance security. The choice between them often depends on the level of security required for a particular system or application. As a general rule, systems that handle sensitive or valuable information are increasingly adopting 2FA to mitigate the risks associated with password-based access.