As discussed in section 3, a group key agreement scheme needs to provide key adjustment protocols stemming from membership changes. TGDHincludes protocols in support of the following operations:
The following sections (5.2 to 5.5), present the four protocols. In each section, we assume that every member can unambiguously determine the sponsorsand the insertion location in the tree (in case of an additive event). Note that the key refresh operation is, in fact, a special case of the leave protocol, without any members leaving the group, where the rightmost shallowest member changes it key share.