What is Two-Factor Authentication (2FA)?
A security method requiring users to provide two different types of identification before accessing an account — typically something they know (password) and something they have (phone or security key).
In plain English
2FA is like a bank vault that requires both a key and a combination. Even if a thief steals the key (your password), they can't open the vault without also knowing the combination (the code on your phone). Two locks are exponentially harder to break than one.
How it works
After entering a password (first factor), the user must provide a second factor — typically a time-based one-time password (TOTP) from an authenticator app, an SMS code, or a physical security key tap. The server verifies both factors before granting access. TOTP apps like Google Authenticator generate codes that change every 30 seconds based on a shared secret.
Why it matters for AI-built apps
Credential stuffing and phishing are rampant. Even strong passwords get compromised through data breaches of other services. 2FA stops the vast majority of account takeover attacks because stolen passwords alone are useless. For apps handling sensitive data, financial transactions, or admin access, 2FA should be strongly encouraged or required.
Common issues
SMS-based 2FA is vulnerable to SIM swapping attacks. Not providing backup recovery codes locks users out permanently. Storing TOTP secrets unencrypted in the database. Not enforcing 2FA for admin accounts. Making 2FA setup too confusing, leading to low adoption. Not rate-limiting 2FA code attempts.
Best practices
Prefer TOTP (authenticator apps) or WebAuthn (security keys) over SMS-based 2FA. Always provide backup recovery codes during setup. Encrypt TOTP secrets at rest. Enforce 2FA for all admin and high-privilege accounts. Rate-limit code verification attempts. Consider offering 2FA as opt-in for regular users but required for admins. Use libraries like speakeasy or otplib for TOTP implementation.
Frequently asked questions
Should I require 2FA for all users or just admins?
At minimum, require 2FA for admin and staff accounts — these have the most access and are the most targeted. For regular users, strongly encourage it but make it opt-in to avoid friction. If your app handles financial or health data, consider requiring it for everyone.
Is SMS-based 2FA good enough?
SMS 2FA is better than no 2FA but has known vulnerabilities — SIM swapping and SS7 attacks can intercept codes. For most apps, it's an acceptable starting point. For higher security needs, use TOTP authenticator apps (Google Authenticator, Authy) or hardware security keys (YubiKey). Never rely on SMS as the sole second factor for admin accounts.
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