The US National Institute for Standards and Technology has released a new draft of its Digital Authentication Guideline, which sets the rules that all authentication software eventually follows. In the document, NIST deprecates the implementation of SMS as a method with which users validate a second level of security on various accounts, "no longer" allowing its use in future guidelines as it is considered not secure enough (via TechCrunch).

Two-factor authentication via SMS (left) and an alternative trusted iOS device (right)

If the out of band verification is to be made using a SMS message on a public mobile telephone network, the verifier SHALL verify that the pre-registered telephone number being used is actually associated with a mobile network and not with a VoIP (or other software-based) service. It then sends the SMS message to the pre-registered telephone number. Changing the pre-registered telephone number SHALL NOT be possible without two-factor authentication at the time of the change. OOB using SMS is deprecated, and will no longer be allowed in future releases of this guidance.

Setting up two-factor authentication through text messages is one of the most popular ways users add another layer of security onto an account, on top of a basic password, including those for Apple's own software, like Apple ID and iCloud. Other than SMS, Apple allows users to implement two-factor authentication through a simple push notification sent to another " trusted device ," or a phone call.

The new guidelines also make a point for companies to ensure that two-factor authentication notifications aren't going through a VoIP service, which could be easily compromised. NIST also includes "limited use" of biometrics as a way for users to gain access to their second layer of authentication, meaning Apple could pivot to Touch ID as an alternative if SMS support for the security feature officially comes to an end.