What is Modern 2FA?
Passwords have very few fans and rightfully so. The end-user impact on usability is something we can all understand. Less widely understood is that passwords expose organizations and our infrastructure to remote, scalable attacks. Several studies including the Verizon Data Breach Investigation Report show credential compromise as the root cause of large scale attacks and highly embarrassing and costly breaches.
Here are some challenges with password-based security:
- Passwords can be guessed, even seemingly strong ones.
- End users need to be able to tell the difference between a good request and a malicious request. An example is Phishing attacks, which can lead people to reveal their passwords.
- Passwords can be stolen en masse from poorly secured repositories. A classic example of this is the Yahoo breach.
- Furthermore, even if you implement a robust password policy for your own site, there's no guarantee that the user won't reuse their password elsewhere
The lengthy list of downsides spurred the development of a retrofit for passwords by augmenting them with an additional means of authentication, otherwise known as two-factor authentication (2FA). However, past approaches to 2FA have their own security issues. Many traditional methods of 2FA have design flaws that have led to organizations like the National Institute of Standards and Technology (NIST) to recommend that they should be deprecated.
The first attempt at 2FA was the arrival of One-Time Password (OTP). In this scenario, the user is given a dedicated OTP-generating hardware device they must carry with them. However, along with typing in their password (the first factor), the user also has to key in the (second factor) OTP value at every login. This increased security, but decreased usability since the user has to carry a special token (often multiple ones) around and transcribe numbers from one screen to another. This quickly becomes unusable, especially on a mobile phone. If an authentication solution has a lot of friction, then adoption may be low and transactions may be reduced.
This setup is also vulnerable to man-In-the-middle (MiTM) and malware attacks. Cost is a problem, because these systems required a proprietary OTP hardware device locked to a specific vendor. OTP systems based on a secret key are also subject to attack, causing massive compromises. Such an attack happened to RSA, requiring a remedy of wholesale token replacement.
Another attempt at 2FA replaced the dedicated OTP device with an app running on the mobile phone. While this eliminates the need to carry around a token, it is still inconvenient and subject to the same security problems as tokens, and more. Yet another attempt relies on transmitting the OTP over SMS. While this offered an improved user experience, it relied on the (weak) security of the SMS network. The use of SMS as an additional means of authentication is itself subject to attack. Recently, hackers broke into a few Reddit systems by intercepting SMS messages.
To effectively augment passwords or just outright replace them, we need a modern approach to 2FA. It needs to combine security with ease of use, and decentralize authentication in a way that cannot be attacked centrally and create a distributed security infrastructure that works across all devices, operating systems and browsers in a non-proprietary, standard way. Modern 2FA is based on FIDO and other open standards, which means freedom from being locked into a particular vendor's hardware or infrastructure.
With the modern 2FA approach, the shortcomings of previous approaches are finally addressed. The first step is to eliminate symmetric shared secrets and replace them with asymmetric key based methods that require no central authority or secret. This overcomes the problem of interception and manipulation of shared secrets endemic to passwords and OTPs.
The second step is to protect the private keys in the secure hardware element within the mobile device (TEE on Android; Secure Enclave on iOS) or PC laptop (TPM). The keys can even be stored on an NFC or Bluetooth-linked external hardware token. The server only stores the public keys, eliminating a major area of vulnerability.
The third step is to tightly couple the usage of the key with a user gesture that can vary from a simple biometric (face, finger, voice) to a wearable or token to a more complex gesture that combines something you have with something you know with something you are in as many combinations as is deemed necessary to achieve the right level of security. The important thing is to keep the developer API and backend the same regardless of which means of authentication is used.
Finally, Modern Authentication should never rely on end-users being able to tell the difference between a good request and an malicious request, and protocols like FIDO add special measures beyond the protection of keys to prevent phishing and MiTM attacks.
By leveraging a modern approach to 2FA, attacks due to credential compromise will be a thing of the past!