Provably secure key-updating schemes in identity-based systems

Abstract

In this paper, we present Key-Updating Schemes in identity-based (identifi- cation or signature) systems, and consider the security of the schemes. We propose two kinds of key-updating schemes, i.e., one is sequential type and the other is parallel type, and show that both schemes arc equivalent to each other in a polynomial time sense, i.e., there exists a deterministic polynomial time algorithm that transforms the sequential key-updating scheme to the par- allel one, and vice versa. We also show that even if any polynomially many entities conspire to find a secret-key of any other entities, both key-updating schemes are provably secure against polynomially many times key-updating if decrypting RSA is hard.