Attack on Digital Multi-Signature Scheme Based on Elliptic Curve Cryptosystem

The concept of multisignature, in which multiple signers can cooperate to sign the same message and any verifier can verify the validity of the multi-signature, was first introduced by Itakura and Nakamura. Several multisignature schemes have been proposed since. Chen et at proposed a new digital multi-signature scheme based on the elliptic curve cryptosystem recently. In this paper, we show that their scheme is insecure, for it is vulnerable to the so-called active attacks, such as the substitution of a "false" public key to a "true" one in a key directory or during transmission. And then the attacker can sign a legal signature which other users have signed and forge a signature himself which can be accepted by the verifier.