The digital signature is a very important subject for network security. Considering multiple signers and multiple verifiers

Xie and Yu (

2004

2004

) pointed out that the multisignature scheme of Laih and Yen (

1996

1996

) is vulnerable to a harmful attack. An attack can occur when a specified group of verifiers cooperate to forge a multisignature by secret key substitution following the leak of a secret key or by group public key adjustment during the process of renewing membership. Xie and Yu proposed an improvement of Laih and Yen’s multisignature scheme. In this paper

we show that Xie and Yu’s scheme is vulnerable to clerk and rogue-key attacks. We propose an improved multisignature scheme to resist such attacks. In the proposed scheme

multiple signers can generate a multisignature for the message with the signers’ secret keys

and the specified group of verifiers can cooperate to verify the validity of the multisignature with the signers’ public keys and the verifiers’ secret key. The proposed scheme for a special verifier group not only has the advantages of Xie and Yu’s scheme

but also is secure against clerk and rogue-key attacks.