Improvement of an Identity-Based Multisignature Scheme

In this paper the security of a multisignature scheme proposed by Harari was analyzed, and an attack method was constructed. An Attacker can successfully steal the signing key of a random signer through such method, and then forge a valid multisignature. The improvement of the original scheme was then proposed. It can be proved that the improved scheme can resist that kind of attack efficiently; the signature efficiency is also promoted at the same time.