SMSOTP

SMSOTP, or Short Message Service One-Time Password, is a method of authenticating a user by delivering a single-use code via SMS. It is commonly employed as a form of two-factor authentication (2FA) or for account recovery and verification flows. The approach relies on the user’s mobile phone number as a second factor beyond a password.

In typical use, a user initiates a login or verification process. The system generates a random numeric code, often six digits, stores it with an expiry time, and sends it through an SMS gateway to the user’s registered mobile number. The user enters the received code on the website or app, where the server validates that the code matches and has not expired. Codes are usually single-use and short-lived to limit exposure.

Security considerations for SMSOTP include its susceptibility to certain attacks, such as SIM swapping, SMS interception, or malware on the device. Because the code travels over mobile networks, it can be compromised by attackers who gain control of the phone number or intercept messages. As such, many security guides recommend using SMSOTP as a secondary factor rather than the sole authentication method, and to pair it with additional protections or to migrate to more phishing-resistant alternatives when possible.

Advantages of SMSOTP include broad compatibility, since it does not require internet access or specialized apps, and easy deployment. Limitations involve delivery delays, carrier dependencies, potential costs, and notable security weaknesses compared with app-based or hardware-based authenticators. Alternatives include time-based one-time passwords generated by authenticator apps, push-based 2FA, and hardware security keys using protocols like WebAuthn.