) Thomas Hardjono 1 ? and Yuliang Zheng 2 ?? 1 ATR Communications Research Laboratories 2-2 Hikaridai, Seika-Cho, Soraku-gun, Kyoto 619-02, Japan 2 Department of Computer Science, University of Wollongong, Australia Abstract. This paper proposes a practical digital multisignature scheme based on the C ? sig cryptosystem derived from the Csig cryptosystem of Zheng and Seberry (1993). The simple scheme consists of three phases. In the first phase the issuer of the document prepares the document, the list of prospective signatories and a pad on which signatories are to write their signatures. In the second phase each signatory verifies the document, signs it and forwards it to the next signatory. In the third phase a trusted verifier or notary decides on the validity of the signatures. The scheme prevents cheating by dishonest signatories from going undetected. The scheme is practical and offers at least the same security level afforded by its underlying cryptosystem against extern...