In the described two-factor authentication process, which sequence correctly represents the steps from setup to verification?

• A. Provide contact; login with username and strong password; receive code; enter code
• B. Login with username and password first; then provide contact; then receive code; enter code
• C. Provide contact; receive code; login with username and password; enter code
• D. Provide contact; login with username and strong password; enter code; receive code

Answer: (A)

Two-factor authentication uses two separate ways to prove who you are: something you know (the password) and something you have access to (a code sent to a registered contact). The setup step is to provide the contact method so the system knows where to send the code. When you sign in, you first enter your username and a strong password. Only after this are you sent a one-time code to your registered contact, and you then enter that code to complete verification. That sequence—provide contact, log in with username and password, receive code, enter code—fits logically and practically, because you need a known contact ready to receive the code, the password must be verified first, and the code must be entered after it’s delivered. The other sequences either try to send or reveal the code before the login step or require entering a code you haven’t received yet, which wouldn’t work in a real 2FA flow.