Hierarchical Functional Signcryption: Notion and Construction

Paper in proceeding, 2019

With the purpose of achieving fine-grained access control over the signing and decryption capabilities in the context of a traditional digital signcryption scheme, the concept of functional signcryption (FSC) is introduced by Datta et al. (ProvSec 2015) to provide the functionalities of both functional encryption (FE) and functional signature (FS) in an integrated paradigm. In this paper, we introduce the notion of hierarchical functional signcryption (HFSC), which augments the standard functional signcryption with hierarchical delegation capabilities on both signcrypting and unsigncrypting, thereby significantly expanding the scope of functional signcryption in hierarchical access-control application. More precisely, our contributions are two-fold: (i) we formalize the syntax of HFSC and its security notion, (ii) we provide a generic construction of HFSC based on cryptographic building blocks including indistinguishability obfuscation (iO) and statistically simulation-sound non-interactive zero-knowledge proof of knowledge (SSS-NIZKPoK) for NP relations, and we formally shows that it satisfies selective message confidentiality and selective ciphertext unforgeability.