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Mecke, Lukas; Rodriguez, Sarah Delgado; Buschek, Daniel; Prange, Sarah; Alt, Florian (2019): Communicating Device Confidence Level and Upcoming Re-Authentications in Continuous Authentication Systems on Mobile Devices. In: Proceedings of the Fifteenth Symposium on Usable Privacy and Security (Soups 2019): pp. 289-301
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Continuous implicit authentication mechanisms verify users over time. In case the device's confidence level (DCL) is too low, the user is prompted with a re-authentication request, which has been shown to annoy many users due to its unpredictable nature. We address this with a novel approach to enable users to anticipate the need for re-authentication with two indicators: (1) a long term indicator shows the current DCL and its development over time, and (2) a short term indicator announces that re-authentication is imminent. In both cases voluntary re-authentication allows the DCL to be raised and a device lock to be avoided. We tested the indicators in a four week field study (N=32). Our results show that both indicators were preferred over giving no indication and that importance and sensitivity of the interrupted task have a strong impact on user annoyance. Voluntary re-authentications were perceived as positive.