The ubiquitous usage of mobile devices in public spaces increases the risk of falling victim to shoulder surfing attacks, i.e. being observed by others during authentication. A promising approach to mitigating such shoulder surfing risks is portfolio authentication. It requires only an authorized subset of the password as input during each authentication attempt. One open challenge regarding portfolio authentication is how to securely and efficiently verify that a user input is actually an authorized subset of the password. In this paper we propose the (t, n)-threshold verification scheme, a novel scheme using Blakley secret sharing to provide secure verification of all authorized subsets of the password. Due to the lack of a viable alternative, we evaluate the efficiency of the (t, n)-threshold verification scheme in comparison to a naive approach. In terms of storage, the (t, n)-threshold verification scheme outperforms the naive approach in all settings and it offers lower computation times in most settings.
['Peter Mayer', 'Melanie Volkamer']
Secure and Efficient Key Derivation in Portfolio Authentication Schemes Using Blakley Secret Sharing