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Usability Evaluation of Randomized Keypad

Young Sam Ryu, Do Hyong Koh, Brad L. Aday, Xavier A. Gutierrez, and John D. Platt

Journal of Usability Studies, Volume 5, Issue 2, Feb 2010, pp. 65 - 75

Article Contents


Numeric keypads are popular input methods for personal identification numbers (PINs) for many applications, including automated teller machines (ATM), security screening systems within financial organizations, point-of-sale systems, and home/car door locks. However, the threat of “shoulder surfing” or observing private information from the well-known layout of numeric keys has inspired the idea of randomizing the layout of keys (Collins, 1990; Hirsch, 1982, 1984; McIntyre et al., 2003; Rehm, 1985).

The proliferation of touch screen interfaces on modern devices such as ATMs has enabled the concept of the randomized keypad. However, very little is known about the overall usability of the randomized numeric keypad. Although research has focused on the prevention of shoulder surfing (Hoanca & Mock, 2005; Roth & Richter, 2006; Tan, Keyani, & Czerwinski, 2005) and the use of picture-based keypads (Komanduri & Hutchings, 2008), the usability of randomized keypads is not covered in the literature.

This study evaluated the overall usability of a randomized numeric keypad. The primary goal of this study was to investigate if users were able to complete the task of entering a PIN via a randomized keypad and to compare this activity to the use of a fixed keypad with a conventional layout. To conduct the test, completion time measurements and error-rate statistics for various tasks were collected via specialized test fixtures. This data provided a valuable metric for the efficiency and accuracy of the use of a randomized keypad. A secondary goal of this study was to investigate whether a randomized keypad enhanced the perceived security of the PIN-entry task, particularly for publicly located systems (ATMs, door locks, etc.). Pre-test and post-test surveys provided subjective data to measure the perceived level of security and user satisfaction.

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