Fully Secure Unbounded Inner-Product and Attribute-Based Encryption

In this paper, we present the first inner-product encryption (IPE) schemes that are

unbounded

in the sense that the public parameters do not impose additional limitations on the predicates and attributes used for encryption and decryption keys. All previous IPE schemes were

bounded

, or have a bound on the size of predicates and attributes given public parameters fixed at setup. The proposed unbounded IPE schemes are

fully (adaptively) secure and fully attribute-hiding

in the standard model under a standard assumption, the decisional linear (DLIN) assumption. In our unbounded IPE schemes, the inner-product relation is generalized, where the two vectors of inner-product can be different sizes and it provides a great improvement of efficiency in many applications. We also present the first

fully secure unbounded

attribute-based encryption (ABE) schemes, and the security is proven under the DLIN assumption in the standard model. To achieve these results, we develop novel techniques,

indexing

and

consistent randomness amplification

, on the (extended) dual system encryption technique and the dual pairing vector spaces (DPVS).