IFTT-PIN: A Self-Calibrating PIN-Entry Method

TL;DR

This paper introduces IFTT-PIN, a self-calibrating PIN-entry method that personalizes interfaces without explicit calibration and enhances security against shoulder surfing attacks, while maintaining usability and memorability.

Contribution

The paper presents IFTT-PIN, the first self-calibrating PIN method that infers user preferences and PINs simultaneously, improving security and usability without explicit calibration.

Findings

Significantly reduced shoulder surfing attack success rate by 8.5 times.

Maintained high PIN entry rates with only a slight decrease.

Enhanced memorability of the interface after 21 days.

Abstract

Personalising an interface to the needs and preferences of a user often incurs additional interaction steps. In this paper, we demonstrate a novel method that enables the personalising of an interface without the need for explicit calibration procedures, via a process we call self-calibration. A second-order effect of self-calibration is that an outside observer cannot easily infer what a user is trying to achieve because they cannot interpret the user's actions. To explore this security angle, we developed IFTT-PIN (If This Then PIN) as the first self-calibrating PIN-entry method. When using IFTT-PIN, users are free to choose any button for any meaning without ever explicitly communicating their choice to the machine. IFTT-PIN infers both the user's PIN and their preferred button mapping at the same time. This paper presents the concept, implementation, and interactive demonstrations of IFTT-PIN, as well as an evaluation against shoulder surfing attacks. Our study (N=24) shows that by adding self-calibration to an existing PIN entry method, IFTT-PIN statistically significantly decreased PIN attack decoding rate by ca. 8.5 times (p=1.1e-9), while only decreasing the PIN entry encoding rate by ca. 1.4 times (p=0.02), leading to a positive security-usability trade-off. IFTT-PIN's entry rate significantly improved 21 days after first exposure (p=3.6e-6) to the method, suggesting self-calibrating interfaces are memorable despite using an initially undefined user interface. Self-calibration methods might lead to novel opportunities for interaction that are more inclusive and versatile, a potentially interesting challenge for the community. A short introductory video is available at https://youtu.be/pP5sfniNRns.