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 this https URL

介绍了一种名为 IFTT-PIN 的自校准 PIN 码输入方法，通过自校准的方式，用户可以自由选择按钮含义，从而提高用户界面的安全性和可用性。实验证明，IFTT-PIN 可显著减少针对 PIN 码的攻击解码率。

IFTT-PIN：一种自校准 PIN 输入方法

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

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
this https URL with a video introduction available at
this https URL. 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.

本文介绍了一种名为 IFTT-PIN 的自校准 PIN 输入方法，它可以自行确定用户选择的按钮 - 颜色映射关系以及用户的密码，从而提高用户的安全性和互动性，并在其它应用领域也可能带来新的交互机会。同时，该方法被提出作为一种新型的应对肩窥攻击的方法。