Security of signature schemes in a multi-user setting

This paper initiates the study of the security of signature schemes in the multi-user setting. We argue that the well-accepted notion of security for signature schemes, namely existential unforgeability against adaptive chosen-message attacks, is not adequate for the multi-user setting. We propose an extension of this security notion to the multi-user setting and show that signature schemes proven secure in the single-user setting can, under reasonable constraints, also be proven secure in the multi-user setting.