  IFTT-PIN is a self-calibrating version of the PIN-entry method introduced in
Roth et al. (2004) [1]. In [1], digits are split into two sets and assigned a
color respectively. To communicate their digit, users press the button with the
same color that is assigned to their digit, which can thus be identified by
elimination after a few iterations. IFTT-PIN uses the same principle but does
not pre-assign colors to each button. Instead, users are free to choose which
button to use for each color. The button-to-color mapping only exists in the
user's mind and is never directly communicated to the interface. In other
words, IFTT-PIN infers both the user's PIN and their preferred button-to-color
mapping at the same time, a process called self-calibration. In this paper, we
present online interactive demonstrations of IFTT-PIN with and without
self-calibration and introduce the key concepts and assumptions making
self-calibration possible. IFTT-PIN can be tested at
https://jgrizou.github.io/IFTT-PIN/ with a video introduction available at
https://youtu.be/5I1ibPJdLHM. We review related work in the field of
brain-computer interface and further propose self-calibration as a novel
approach to protect users against shoulder surfing attacks. Finally, we
introduce a vault cracking challenge as a test of usability and security that
was informally tested at our institute. With IFTT-PIN, we wish to demonstrate a
new interactive experience where users can decide actively and on-the-fly how
to use an interface. The self-calibration paradigm might lead to novel
opportunities for interaction in other applications or domains. We hope this
work will inspire the community to invent them.
