# OTP and two-factor authentication explained

The code you type is the simplest piece of security on the internet, and still the most common.

## What is an OTP?

An OTP (one-time password) is a short code valid for one login or action, delivered by SMS, email, voice or generated by an authenticator app. Two-factor authentication uses it as a second proof after the password. SMS OTPs are convenient but can be intercepted by SIM swap or phishing; authenticator apps and passkeys are stronger.

## Types of second factor

- SMS or voice code: anything that receives at that number.
- TOTP app: time-based code generated on your device.
- Push: approve on a trusted device.
- Passkey or hardware key: cryptographic, phishing-resistant.

## Temporary numbers and 2FA

Use a temporary number to pass sign-up verification, then move the second factor to an authenticator app. If the service only offers SMS 2FA, rent the number so it remains yours at the next login.

## FAQ

**Is SMS 2FA better than nothing?** Much better. It stops password-only attacks, which are the majority.

**Is SMS 2FA safe enough?** Better than password only; weaker than an authenticator app or a passkey. Use the app where possible.

**Can I use a temporary number as my 2FA number?** Only a rented one, kept renewed. A one-time number will not receive future codes.

**What is a passkey?** A cryptographic login tied to your device, resistant to phishing. Many services now offer it instead of SMS.

Published: 2026-10-30

Source: https://smsnitro.com/blog/what-is-otp-and-two-factor-authentication