Provable security of identity-based encryption-signature schemes

Abstract

After the advent of the concept of provable security, there have been lots of results proving the security of cryptographic schemes theoretically. However, the coverage of those proof is limited to a single scheme. This means that in practice, if somebody congures a combination of two or more schemes, such as encryption and signature, some security vulnerabilities that a scheme compromises the other schemes may happen. So far, there has been few results on a combination of existing cryptographic schemes. In this paper, we begin a rigorous study of the security of the combination of an encryption scheme and a signature scheme. We give a formal de finitions of the combination of those schemes which we call an encryption-signature (ES). As a variant we also consider an identity-based version which we call an identity-based encryption-signature (IDB-ES). We propose security models of these schemes. Assuming hash functions are random oracles, we prove the security of an IDB-ES scheme obtained by combining a practical identity-based encryption scheme of Boneh-Franklin and signature scheme of Cha-Cheon. Our IDB-ES scheme is secure if Bilinear Di e-Hellman Problem is intractable.