Signing in to a service

Multi-factor authentication using text message

A code is shown in a text message on a mobile device and entered into a computer at the same time.


Multi-factor authentication adds an extra layer of security on top of a username and password. In this kind of multi-factor authentication, a service sends someone a text message with a unique code which they can use to access the service. The code is unique to that person and device. It’s single-use and expires after a short period of time. When installing a mobile banking app, for example, a customer receives a code that they enter to complete the setup.

IF thinks this is a useful pattern because it adds another layer of security to someone’s account. It does increase friction, though. Someone has to have their phone nearby and wait for a text message. It also relies on infrastructure (SS7) that has many known vulnerabilities. Therefore, it is worth adding options for multi-factor authentication patterns that suit different contexts, including multi-factor authentication using a code generator.


  • Makes it more difficult for an unauthorised person to access user’s data or devices.
  • If one security factor is compromised, the attacker has another barrier to get through.
  • Works on any phone.
  • No need for an internet connection.
  • Can sometimes be automatically read by apps so that people don’t have to open messages to use the codes.


  • Need to have phone nearby.
  • Messages may be delayed.
  • Requires phone signal.
  • Doesn’t prevent phishing attacks.
  • Relies on infrastructure (SS7) with many known vulnerabilities.