We give characterizations for generalized functions invariant under certain group actions, such as groups of rotations and the Lorentz group. In the case of rotations, it answers an open question by M. Oberguggenberger in [3]. Also general one-parameter groups are considered.

The concept of group signatures was introduced by Chaum et al. at Eurocrypt '91. It allows a member of a group to sign messages anonymously on behalf of the group. In case of a later dispute a designated group manager can revoke the anonymity and identify the originator of a signature. In this paper we propose a new eecient group signature scheme. Furthermore we present a model and the rst real...