Two-factor authentication is not an ideal solution. Yes, multi-factor authentication improves security in comparison with most single-factor authentication solutions. However, it comes with a price. Not only can implementing a multi-factor authentication solution actually cost you quite a lot of money, it also risks compromising user convenience. More ideal solutions should exist.
# Two-factor authentication worsens user friendliness
One might argue that a two-factor authentication solution does improve both user convenience and security. After all, a multi-factor approach lessens dependency on the first factor, usually a username and password combination. This allows picking easier to remember passwords. It is true that for those who were used to using complex passwords, a second factor improves user convenience. However, for users that already used simple and easy to remember passwords, the second factor will improve security but worsens user friendliness. For them the new authentication solution requires more time and hassle to log in in comparison with a single-factor approach.
For users who use simple passwords, the second factor worsens user friendliness.
There are a lot of good two-factor solutions out there. And it cannot be denied that these are becoming more and more user friendly. Consider one-time-passwords via SMS, security keys, mobile authentication apps, and many other solutions. Personally, I am a fan of the Universal Second Factor (U2F) standard, which indeed is a standard for two-factor authentication But, no! Even U2F products do not provide ideal solutions.
# Imagine the ideal solution for authentication
Not a single multi-factor approach fully solves the paradoxical tension between security and user convenience. Although, every two-factor authentication solution helps most users to improve security without compromising a lot on user friendliness, it does improve the burden for other users. Moreover, we should not underestimate the complexity of managing multi-factor solutions for service providers. All considered together, the multi-factor approach could never provide an ideal solution.
But what would then be this ideal solution for authentication? Stating a fantasy, a dream of what would be the desired end result allows building a path to the solution. Innovation starts by writing a perspective that provokes the accepted truth that user convenience and security are in a trade-off relationship. (See "And Suddenly the Inventor Appeared" by G. Altshuller)
Innovation starts by provoking the accepted truth that user convenience and security are in a trade-off relationship.
An ideal solution for authentication would be a system that is able to confirm your identity without requiring you to do anything. There would be no need to present a username, a one-time-password or a fingerprint. In an ideal situation authentication happens transparently, while fully respecting your privacy. An ideal authentication solution would not bother the user with something he knows, something he has, or something the user is. An ideal solution provides maximum security without compromising user convenience.
Is this a fantasy? Let's hope not. Let it be the future of authentication!
# The future of authentication
Two-factor authentication solutions do not fit in this far future perspective. This does not mean that it does not provide any good in the present. We cannot conclude to stop implementing multi-factor solutions now. However, by realizing that current best practices are not ideal we become aware of the possibility for better solutions. These might not exist today. Innovation will help creating these tomorrow.