We present an 1-out-of-n noninteractive OT(Oblivious Transfer) protocol based on the Diffle-Hellman assumption and a new fair exchange scheme of secret information among multi-users. Using the noninteractive OT protocol and the fair exchange scheme, we also present a new digital multisignature scheme based on Fiat-Shamir signature scheme and analyze its security. Owing to its concurrency, viability, and dishonesty detectablility, the proposed digital multisignature scheme is applicable to electronic multi-user contract systems.