Yahoo recently rolled out a new way for users to access their services without entering a password. Their new system uses a cellphone to authenticate the user. Instead of entering a password, the user receives a verification code via text message on their phone. (The user would have provided their phone number to Yahoo when setting this option up.) Once the user receives this code, they enter it on the Yahoo login page and voilà!, they’re logged in.
So what’s wrong with this? Is this a wonderful advance in the field of authentication?
The intentions are good. It is encouraging that online services are putting thought and effort into making their users’ lives easier and more secure. However, a cold analysis of this method finds that it’s not a particularly secure solution.
Fundamentally, it’s still a single-factor method of authentication. This means that it does not offer any additional security by itself. If the single factor is compromised, you still lose control of your account. In the same way that losing/forgetting your password prevents you from accessing your email, losing or forgetting your phone does the same.
However, that’s something we already knew. The real question is: is this method more secure than ordinary passwords?
What this method means is that an attacker who has control of the user’s phone has complete access to his Yahoo account as well. However, some people (like me) forget phones more than they forget passwords. In that case, someone who has my phone would also be able to access my Yahoo account if I left an indication what my Yahoo user name is on the phone. (While the email can be easily accessed from an app, other Yahoo services may be best used via a browser.)
More than that, text messages themselves can also be intercepted by mobile malware. Sometimes it’s for blackmail and extortion. Other times, it’s to steal online banking transaction codes. Other times, it’s to hide premium subscriptions. It’s not out of the question that a Yahoo user’s account credentials could be stolen in this manner.
This authentication process can also be used (and abused) for various purposes, for example, if your phone can’t be found but is nearby – if it’s tied to a Yahoo account this way, it can be used as an impromptu phone locator. Similarly, the authentication process can be used to spam or annoy someone who’s tied their phone to their Yahoo account.
Overall, is it more convenient to use this method? Sure. Is it more secure? Not at all. If you’re going to do this at all, make sure you never forget your phone anywhere – or at least leave it behind less often than you forget your password. Don’t forget to use any security features your phone has (such as screen lock, etcetera) to keep it as secure as possible if it is lost.
If you do want to secure your Yahoo account, there’s a better way to do so. Yahoo has supported two-step verification since 2011. This also uses a code sent to the phone to log the user in, but this is in addition to the user’s existing password.