Common use of Merge Protocol Clause in Contracts

Merge Protocol. The communication overhead of the merge protocol may appear high. However, this is not the case. Let us assume merging groups. In the first round, a sponsor in each group broadcasts its key tree after updating its session random. Upon receiving these broadcast messages, every member rebuilds a key tree which has some missing bkeys. At most paths will have missing bkeys. Propagating these bkeys requires at most rounds, since each sponsor (in each subsequent round) computes bkeys as far as it can. Therefore, a merge of groups takes at most rounds. The maximum number of messages is . The number of modular exponentions for the worst and the best case is same as that of join protocol, since rebuilding the whole key tree requires same amount of serial number of modular exponentions as joining to the leaf node. Figure 9 shows an example of two merging groups, where the sponsors and broadcast their trees ( and