Abstract
We propose a novel group-oriented signature scheme, called a democratic group signature (DGS). In DGS the scheme setting is controlled on a contributory basis, i.e., without any centralized trusted authority (group manager). Group members agree on a common tracing trapdoor, i.e., every member can trace issued signatures individually. Members are able to sign on behalf of the group while remaining anonymous only to third parties. DGS supports dynamic changes of the group formation (joins and leaves of members). For security reasons the tracing trapdoor is updated after every dynamic change. The DGS model results from strong changes to the standard model of group signatures caused by elimination of the group manager's role and distribution of the tracing rights to individuals.