Introduction

The demand for user devices has grown rapidly in the last decade. This has been facilitated by technological advancements making devices cheaper, faster, and more available. Such devices are now commonplace in both our personal and professional lives because of the plethora of capabilities these devices have. However, to utilise these capabilities a user must often store private data that is accessible on the device (such as account information, emails/messages, and photos). This information could be used for malicious purposes if it were obtained by imposters. Most devices now include the functionality for a user to enable an authentication mechanism (such as a PIN or fingerprint). Though, whilst the capabilities of devices have advanced significantly, the way users authenticate themselves has followed a security paradigm that has not changed. This paradigm authenticates only at the point-of-entry and often does so at the cost of intrusiveness and inconvenience. There are, therefore, both security and usability issues with current device authentication mechanisms. The concept of authentication systems that can transparently and continuously authenticate users via their biometrics offers a way to improve device security and enhance both security and usability.