Abstract: Using an homomorphic authenticator (HA) scheme (e.g.?, ?homomorphic MAC or signature?) a user, Alice, can authenticate a collection of data items using her secret key, and send the authenticated data to an untrusted server. At any later point in time, the server can generate a short authenticator vouching for the correctness of the output of a function computed on the outsourced data to another user Bob. However, how can we authenticate homomorphic computation of functions that involve data authenticated by different users holding independent secret keys? In this talk I will present two solutions to create multi-key homomorphic authenticators. I will describe the first multi-key homomorphic MAC construction by Fiore et al?. (Asiacrypt 2016) and the first compiler to enhance any sufficiently expressive single-key homomorphic signature with multi-key properties (Fiore and Pagnin, to appear at SCN 2018). 

About the speaker: Elena Pagnin is a PhD Student at the Department of Computer Science & Engineering in Chalmers University of Technology (Göteborg - Sweden). She is part of the Chalmers Security Lab which is the largest research group on security in Scandinavia. Her PhD is a blend of theoretical cryptography and cryptographic protocols for real-world applications.