On the Security of Huang-Chang Multi-signature Schemes

Recently, based on RSA and discrete logarithm with composite modulus, Huang and Chang proposed two multisignature schemes with distinguished signing authority and claimed that their scheme can resist forgery attack. Unfortunately, in this works, we show that their schemes have forgery attack by security analysis of Huang-Chang multi-signature schemes. Given a multisignature of certain a document, arbitrary one can forge a multisignature. To overcome the weakness of the schemes, we proposed an improved scheme.