International Association
for Cryptologic Research

Functional encryption (FE) enables sophisticated control over decryption rights in a

multi-user scenario, while functional signature (FS) allows to enforce complex constraints on signing

capabilities. This paper introduces the concept of functional signcryption (FSC) that aims to

provide the functionalities of both FE and FS in an unified cost-effective primitive. FSC provides

a solution to the problem of achieving confidentiality and authenticity simultaneously in digital

communication and storage systems involving multiple users with better efficiency compared to a

sequential implementation of FE and FS. We begin by providing formal definition of FSC and formulating

its security requirements. Next, we present a generic construction of this challenging primitive

that supports arbitrary polynomial-size signing and decryption functions from known cryptographic

building blocks, namely, indistinguishability obfuscation (IO) and statistically simulation-sound noninteractive

zero-knowledge proof of knowledge (SSS-NIZKPoK). Finally, we exhibit a number of representative

applications of FSC: (I) We develop the first construction of attribute-based signcryption

(ABSC) supporting signing and decryption policies representable by general polynomial-size circuits

from FSC. (II) We show how FSC can serve as a tool for building SSS-NIZKPoK system and IO, a

result which in conjunction with our generic FSC construction can also be interpreted as establishing

an equivalence between FSC and the other two fundamental cryptographic primitives.