User Perceptions of Security and Usability of Mobile-Based Single Password Authentication and Two-Factor Authentication

Abstract

Two-factor authentication provides a significant improvement over the security of traditional password-based authentication by requiring users to provide an additional authentication factor, e.g., a code generated by a security token. In this decade, single password authentication (SPA) schemes are introduced to overcome the challenges of traditional password authentication, which is vulnerable to the offline dictionary, phishing, honeypot, and man-in-the-middle attacks. Unlike classical password-based authentication systems, in SPA schemes the user is required to remember only a single password (and a username) for all her accounts, while the password is protected against the aforementioned attacks in a provably secure manner.

In this paper, for the first time, we implement the state-of-the-art mobile-based SPA system of Acar et al. (2013) as a prototype and assess its usability in a lab environment where we compare it against two-factor authentication (where, in both cases, in addition to the password, the user needs access to her mobile device). Our study shows that mobile-based SPA is as easy as, but less intimidating and more secure than two-factor authentication, making it a better alternative for online banking type deployments. Based on our study, we conclude with deployment recommendations and further usability study suggestions.

D. İşler—Work done at Koç University.

A Mobile-Based Single Password Authentication Scheme of Acar et al. [4]

We briefly present Acar et al. [4] mobile-based SPA solution here for completeness. In their mobile-based SPA, there are three parties; a user holding a password pwd, a trusted mobile device of the user, and a server, with which the user wishes to register. The protocol is roughly as follows:

Registration:

• 1. The user:

  • generates a Message Authentication Code (MAC) key K.

  • sends the key K and her username UID to the server.

  • encrypts the MAC key K where the encryption key is derived using the hash of her password H(pwd) as $ctext\leftarrow Encrypt(H(pwd),K)$. [Remark: The user also sends an identifier with ciphertext.]

• 2. The trusted mobile device stores the ciphertext ctext.

• 3. The server stores the username UID and the MAC key K.

Authentication:

• 1. The user sends her username UID to the server.

• 2. The server generates a random challenge chal and sends it to the mobile device. [Remark: The server can send the challenge in various ways such as via SMS, or via a QR code where the user scans the code with her mobile device.]

• 3. The user types her single password on the mobile device.

• 4. The trusted mobile device:

  • decrypts the ciphertext and retrieves the MAC key K as $K\leftarrow Decrypt(H(pwd),ctext)$.

  • generates a MAC resp as a response to the challenge chal using the retrieved key K as $resp \leftarrow MAC(K,chal)$. [Remark: To resist man-in-the-middle attacks, as [19] notes, preferable usage is $resp \leftarrow MAC(K,chal || domain)$.]

  • applies trimming function Trim on the generated response resp to get a short one-time code/password $resp'$ as $resp' \leftarrow Trim(resp)$.

• 5. The user types the short one-time code $resp'$ on the user machine and sends it to the server.

• 6. The server checks if the $resp'$ is generated based on a valid MAC of the challenge chal with the corresponding user MAC key K in his database as $Trim(MAC(K,chal)){\mathop {=}\limits ^{?}} resp'$.

• 7. The server informs the user whether the login attempt is successful or not.