What is an OTP code?

Definition and Basic Principle#

A One-Time Password (OTP) is a randomly generated security code valid for a single use or for a limited period. Unlike a traditional password, an OTP cannot be reused, which enhances the security of online access.

What is an OTP Code Used For?#

OTP codes are primarily used for two-factor authentication (2FA). They add an extra layer of security when logging into an online account (banking, social media, email, etc.).

Even if a hacker steals your password, they cannot access your account without the OTP, which is usually sent to your phone or generated by a dedicated app.

How Does an OTP Code Work?#

There are several ways to receive or generate an OTP code:

• Via SMS: the code is sent directly to your phone number.
• Via email: the code is sent to your email inbox.
• Via an authentication app (Brennus OTP, Google Authenticator, Microsoft Authenticator, etc.): the app generates a code that changes every 30 seconds.
• Via push notification: some apps send an alert to your smartphone to confirm login.

Advantages and Limitations#

Advantages#

• Enhanced security against hacking and phishing.
• Reduced risks associated with password reuse.
• Ease of use for the end user.

Limitations#

• Dependence on phone or internet access to receive the code.
• Risk of losing or having your phone stolen, making access impossible without a backup solution.
• Potential vulnerability if SMS is intercepted (SIM swapping attacks).

Examples of Use#

• Logging into an online bank account.
• Confirming a purchase on an e-commerce site.
• Accessing a social network or professional email.

Best Practices#

• Never share your OTP code with anyone.
• Use an authentication app instead of SMS whenever possible.
• Enable notifications to be alerted in case of suspicious login attempts.

Sources

• ANSSI (Agence nationale de la sécurité des systèmes d’information) – Recommandations sur l’authentification forte.
• CNIL (Commission nationale de l’informatique et des libertés) – Guide sur la protection des données personnelles.
• Google – Documentation sur l’authentification à deux facteurs.
• Wikipedia – Article « One-time password ».