Implementing Two-Factor Authentication

B.

Two-factor authentication (2FA) is a security mechanism that requires two different authentication factors to verify the identity of a user. The two factors could be something you know (like a password), something you have (like a smart card or token), or something you are (like a biometric characteristic such as a fingerprint or iris scan).

Out of the given options, only option D, a datacenter mantrap requiring fingerprint and iris scan, implements two-factor authentication. This is because it requires two different biometric characteristics to verify the identity of a user.

Option A, a phone system requiring a PIN to make a call, only implements single-factor authentication. It only requires something you know (the PIN) to verify your identity.

Option B, an ATM requiring a credit card and PIN, also only implements single-factor authentication. It requires something you have (the credit card) and something you know (the PIN), but both factors fall under the category of something you know.

Option C, a computer requiring username and password, also only implements single-factor authentication. It only requires something you know (the username and password) to verify your identity.

In summary, option D is the correct answer as it is the only option that implements two-factor authentication by requiring two different biometric characteristics to verify the identity of a user.