collective signature

Definition

a group signature scheme, that (i) is shared by a set of signing groups and (ii) combined collective signature shared by several signing groups and several individual signers. The protocol of the first type is constructed and described in detail. It is possible to modify the described protocol which allows transforming the protocol of the first type into the protocol of the second type. The proposed collective signature protocols have significant merits, one of which is connected with possibility of their practical using on the base of the existing public key infrastructures.
Source

Collective signature have a variable length as a function of the number of signers.