Rotem Tsabary (Weizmann Institute of Science)
Wednesday, 27.6.2018, 12:30
In Attribute-Based Signatures an authority can generate multiple signing keys, where each key is associated with a constraint f. A key respective to f can sign a message x only if f(x)=0. The security requirements are unforgeability and key privacy (signatures should not expose the specific signing key used). In Homomorphic Signatures, given a signature for a data-set x, one can evaluate a signature for the pair (f(x),f), for functions f. In context-hiding HS, evaluated signatures do not reveal information about the pre-evaluated signature.
We show that these two notions are in fact equivalent, and construct a new ABS candidate from a worst case lattice assumption (SIS). The first implication of this equivalence is a new lattice-based ABS scheme for polynomial-depth circuits, based on the HS construction of Gorbunov, Vaikuntanathan and Wichs (GVW; STOC 2015). In the opposite direction, our new ABS implies a new lattice-based HS scheme with different parameter trade-off, compared to the aforementioned GVW