Further Remarks on Identity-Based RSA Multi-signature

RSA is a popular public key cryptology for encryption and signing messages. In 2008, Harn and Ren introduced a new identity-based RSA multi-signature scheme by adopting Shamir's signature scheme. But, we find that there are some flaws in their proposal: First, the original signer's signing secret key can be derived. Second, the verification equation will never hold even if the received signature and message are legal. Third, transmission environments are not taken into consideration. This manuscript will thoroughly make discussions on Harn and Ren's scheme by showing the mentioned flaws.