We now describe the protocols that make up the STRkey management suite: join, leave, merge, and partition. All protocols share a common framework with the following features:
Each group member contributes an equal share to the group key; this share is kept secret by each group member.
The group key is computed as a function of all current group members' shares.
As the group grows, new members' shares are factored into the group key while remaining members' shares stay unchanged.
As the group shrinks, departing members' shares are removed from the new group key and at least one remaining member changes its share.
All protocol messages are signed by the sender, i.e., we assume an authenticated broadcast channel.
Before describing the protocols in detail, we review the basic STRkey agreement protocol and the notation used in the rest of the paper.