Using Episodic Memory for User Authentication

Passwords are widely used for user authentication, but they are often difficult for a user to recall, easily cracked by automated programs, and heavily reused. Security questions are also used for secondary authentication. They are more memorable than passwords, because the question serves as a hint to the user, but they are very easily guessed. We propose a new authentication mechanism, called “life-experience passwords (LEPs).” Sitting somewhere between passwords and security questions, an LEP consists of several facts about a user-chosen life event—such as a trip, a graduation, a wedding, and so on. At LEP creation, the system extracts these facts from the user’s input and transforms them into questions and answers. At authentication, the system prompts the user with questions and matches the answers with the stored ones. We show that question choice and design make LEPs much more secure than security questions and passwords, while the question-answer format promotes low password reuse and high recall.

Specifically, we find that: (1) LEPs are 10⁹--10¹⁴ × stronger than an ideal, randomized, eight-character password; (2) LEPs are up to 3 × more memorable than passwords and on par with security questions; and (3) LEPs are reused half as often as passwords. While both LEPs and security questions use personal experiences for authentication, LEPs use several questions that are closely tailored to each user. This increases LEP security against guessing attacks. In our evaluation, only 0.7% of LEPs were guessed by casual friends, and 9.5% by family members or close friends—roughly half of the security question guessing rate. On the downside, LEPs take around 5 × longer to input than passwords. So, these qualities make LEPs suitable for multi-factor authentication at high-value servers, such as financial or sensitive work servers, where stronger authentication strength is needed.