ZEBRA: Zero-Effort Bilateral Recurring Authentication (Companion report)

We describe and evaluate Zero-Effort Bilateral Recurring Authentication (ZEBRA) in our paper that appears in IEEE Symposium on Security and Privacy, May 2014. In this report we provide a more detailed comparative evaluation of ZEBRA against other related authentication schemes. The abstract of the paper follows. Common authentication methods based on passwords, tokens, or fingerprints perform one-time authentication and rely on users to log out from the computer terminal when they leave. Users often do not log out, however, which is a security risk. The most common solution, inactivity timeouts, inevitably fail security (too long a timeout) or usability (too short a timeout) goals. One solution is to authenticate users continuously while they are using the terminal and automatically log them out when they leave. Several solutions are based on user proximity, but these are not sufficient: they only confirm whether the user is nearby but not whether the user is actually using the terminal. Proposed solutions based on behavioral biometric authentication (e.g., keystroke dynamics) may not be reliable, as a recent study suggests. To address this problem we propose ZEBRA. In ZEBRA, a user wears a bracelet (with a built-in accelerometer, gyroscope, and radio) on her dominant wrist. When the user interacts with a computer terminal, the bracelet records the wrist movement, processes it, and sends it to the terminal. The terminal compares the wrist movement with the inputs it receives from the user (via keyboard and mouse), and confirms the continued presence of the user only if they correlate. Because the bracelet is on the same hand that provides inputs to the terminal, the accelerometer and gyroscope data and input events received by the terminal should correlate because their source is the same ‐ the user’s hand movement. In our experiments ZEBRA performed continuous authentication with 85 % accuracy in verifying the correct user and identified all adversaries within 11 s. For a different threshold that trades security for usability, ZEBRA correctly verified 90 % of users and identified all adversaries within 50 s. ZEBRA [10] is a token-based authentication scheme that authenticates users based on their interactions with the device. Unlike keystroke-based biometrics that authenticates users based how they type, ZEBRA authenticates users based on what interactions (e.g., typing, scrolling) they perform on the device and when. In ZEBRA users wear a wrist-bracelet (token) that has built-in accelerometer and gyroscope sensors and a short range wireless radio to communicate with the device. ZEBRA authenticates users by monitoring their hand movements, using the senors in the wrist-bracelet, when they are interacting with the device, and comparing the hand movements with the inputs received by the device during the interaction. In ZEBRA the bracelet contains the identification information for its associated user, which it shares with the device to authenticate the user. The user can associate the bracelet with herself when she wears the bracelet, say by entering a PIN on the bracelet or through a secure channel to the bracelet. The bracelet clasp can detect when it is being taken off and it de-associates with the user when it is taken off.