To Have and Have Not: Variations on Secret Sharing to Model User Presence

Quentin Stafford-Fraser, Frank Stajano, Chris Warrington, Graeme Jenkinson, Max Spencer, Jeunese Payne
Proceedings of the 2014 ACM International Joint Conference on Pervasive and Ubiquitous Computing
We address the problem of locking and unlocking a device, such as a laptop, a phone or a security token, based on the absence or presence of the user. We detect user presence by sensing the proximity of a subset of their possessions, making the process automatic and effortless. As in previous work, a master key unlocks the device and a secret-sharing scheme allows us to reconstruct this master key in the presence of k-out-of-n items. We extend this basic scheme in various directions, e.g. by allowing items to issue a dynamically variable number of shares based on how confident they are that the user is present. The position we argue in this paper is that a multi-dimensional approach to authentication that fuses several contextual inputs, similar to that already adopted by major web sites, can also bring advantages at the local scale.

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