In dynamic networks with flexible memberships, group signatures and distributed signatures are an important problem. Dynamic threshold cryptosystems are best suited to realize distributed signatures in dynamic (e.g. ad-hoc) networks. Without a group manager or a trusted third party even more flexible scenarios can be realized. The researcher showed, it is possible to dynamically increase the size of the signer group, without altering the public key. The authors extend this idea by removing members from the group, also without changing the public key. This is an important feature for dynamic groups, since it is very common, e.g. in ad-hoc networks that members leave a group.