Twitter recently disabled SMS-based two-factor authentication (2FA) except for Twitter Blue subscribers. While the intended results may be cost-savings and boosting the number of subscribers, the decision is likely to have unintended security consequences. Even some tech-savvy people who know and care about security find Twitter's 2FA alternatives awkward enough to delay until they are forced into it, so Twitter's new policy will likely result in fewer accounts using 2FA. Educating users about how to set up authenticator apps and security keys is one solution. But that's analogous to building a faster horse.
Fundamentally, the enterprise 2FA playbook cannot be applied to consumer scenarios in equal measure because consumers can vote with their feet. Any added step will send them galloping into the arms of the competition. Thus, the Twitter news should be a call for disruption, and for solutions that protect consumer identities without introducing friction. I believe that technology is passkeys when available uniformly across the digital landscape.
The State of Consumer MFA
It’s broadly accepted that any multifactor authentication (MFA) is better than no MFA (I’ll use MFA here to mean authenticating your identity with two or more factors). MFA solutions prevent bad actors from accessing resources using only a victim's primary credentials. Our CISO once observed that MFA and adaptive authentication would have prevented 95% of the breaches she has seen.
But not all MFA is created equal. Some factors are weaker than others, particularly against targeted attacks. Security questions, SMS, voice, and email-based one-time passwords are considered low-assurance factors. All these factors are vulnerable to phishing. Attackers can bypass weaker factors by "guessing" the authenticator code; intercepting the code-containing SMS; or creating "alert fatigue" by bombarding the user with messages until they complete the MFA challenge.
MFA Bypass Attacks
Recent research found more than 113 million MFA bypass (registration required) attempts against consumer and SaaS applications over a 90-day period, representing the highest baseline level of attacks of any year on record. Given what we know about weaker factors, you'd be forgiven for thinking Twitter's decision to disable text-based authentication is a good one. But as with most things in identity, there is more complexity that meets the eye, particularly when we look at MFA adoption issues.
The Trouble With MFA Adoption
The challenge of getting users to sign up for any form of MFA lies in the technology's origin story. Passwords predate modern online services by thousands of years (just think about "Open, Sesame" in "Ali Baba and the 40 Thieves"). Two-factor authentication entered the picture much later as a way for enterprises and governments to protect their internal systems with something you know (password) and something you have (device, code, or security key).
Technologies developed in an enterprise context have historically prioritized security. The administrator has the power to enforce security measures across the employee base to protect the company's interests. When organizations try to use the same playbook with consumers, they fail, because consumers can vote with their feet. And the impact can quickly become existential.
So, what about authenticator apps? For us in the industry, this might look like the obvious technical alternative to SMS-based methods. But few end users are this digitally savvy. The more likely result of forcing something like an authenticator app or security key at scale is that people just won't use it.
The transition to phishing-resistant factors offers one potential solution to consumer MFA woes. FIDO and WebAuthn rely on public key cryptography and biometrics to significantly improve both security and the user experience. When using public key cryptography, there are no codes or secrets to be stolen. Users go through a biometric check on their device to unlock access to their private key, which is way faster than entering an SMS code. There are nuances in how biometric data is validated that can make a big difference for data privacy and security.
The Passkeys Opportunity
Despite exciting progress toward more secure and usable factors, the best MFA mechanism for consumers really isn't MFA at all — it's passkeys. Passkeys are a FIDO authenticator with the advantage of being backed up to the cloud, so if you lose your device or buy a new one, all you must do is sign into your iCloud or Google Play account to recover your passkeys. Passkeys use public key cryptography and device biometrics, making them resistant to many known attacks, and are easy for the user.
Should passkeys have been used on Twitter? Absolutely, but they may not have been a clear option at the time. Supporting something new is always expensive from the engineering perspective. If passkeys had been an option, the experience for the user might have looked something like this:
- The user signs into Twitter on their mobile device with username and password;
- They are asked if they would like to use a passkey to authenticate next time; and
- The user receives a biometric prompt from then on without needing to install anything. They can even go to their Mac and open Twitter in Safari, and the passkey will be automatically synced to that device.
Offering passkey authentication currently requires some reworking, but it's easier and more cost-effective than SMS. Unfortunately, passkeys are not yet uniformly distributed. Apple added support early on, followed by Android and Chrome. Windows currently supports passkeys on a single device.
Whenever you're asking people to change, you need to take concrete steps to make the transition easier. In the case of Twitter, that would be explaining to users what they can do to change their second factor, to avoid them dropping MFA entirely. This would be an amazing passkey adoption opportunity if the industry were ready. We're already in a fantastic position to encourage people to use this flavor of passwordless. What comes next is making it easier for developers to implement the necessary changes in their apps and websites. A future with fewer passwords may not be so far away after all.