Common use of Join Protocol Clause in Contracts

Join Protocol. We assume the group has members: . The new member initiates the protocol by broadcasting a join request message that contains its own bkey . This message is distinct from any JOIN messages generated by the underlying group communication system, although, in practice, the two might be combined for efficiency’s sake. Each current member receives this message and determines the insertion point in the tree. The insertion point is the shallowest rightmost node, where the join does not increase the height of the key tree. Otherwise, if the key tree is fully balanced, the new member joins to the root node. The sponsor is the rightmost leaf in the subtree rooted at the insertion node. Next, each member creates a new intermediate node and a new member node, and promotes the new intermediate node to be the parent of both the insertion node and the new member node. After updating the tree, all members, except the sponsor, block. The sponsor proceeds to update its share and compute the new group key; it can do this since it knows all necessary bkeys. Next, the sponsor broadcasts the new tree which contains all bkeys. All other members update their trees accordingly and compute the new group key (see Proposition 2). It might appear wasteful to broadcast the entire tree to all members, since they already know most of the bkeys. However, since the sponsor needs to send a broadcast message to the group anyhow, it might as well include more information which is useful to the new member, thus saving one unicast message to the new member (which would have to contain the entire tree). Figure 3 shows an example of member joining a group where the sponsor ( ) performs the following actions: 1. renames node to Step 1: The new member broadcasts request for join. Step 2: Every member update key tree by adding new member node and new intermediate node, removes all keys and bkeys from the leaf node related to the sponsor to the root node. The sponsor additionally generates new share and computes all [ ] pairs on the key-path, broadcasts updated tree including only bkeys. Step 3: Every member computes the group key using .

Join Protocol. We assume the group has members: . The new member initiates the protocol by broadcasting a join request message that contains its own bkey . This message is distinct from any JOIN messages generated by the underlying group communication system, although, in practice, the two might be combined for efficiency’s sake. Each current member receives this message and determines the insertion point in the tree. The insertion point is the shallowest rightmost node, where the join does not increase the height of the key tree. Otherwise, if the key tree is fully balanced, the new member joins to the root node. The sponsor is the rightmost leaf in the subtree rooted at the insertion node. Next, each member creates a new intermediate node and a new member node, and promotes the new intermediate node to be the parent of both the insertion node and the new member node. After updating the tree, all members, except the sponsor, block. The sponsor proceeds to update its share and compute the new group key; it can do this since it knows all necessary bkeys. Next, the sponsor broadcasts the new tree which contains all bkeys. All other members update their trees accordingly and compute the new group key (see Proposition 2). It might appear wasteful to broadcast the entire tree to all members, since they already know most of the bkeys. However, since the sponsor needs to send a broadcast message to the group anyhow, it might as well include more information which is useful to the new member, thus saving one unicast message to the new member (which would have to contain the entire tree). Figure 3 shows an example of member joining a group where the sponsor ( ) performs the following actions: 1. renames node to Step 1: The new member broadcasts request for join. Step 2: Every member update key tree by adding new member node and new intermediate node, removes all keys and bkeys from the leaf node related to the sponsor to the root node. The sponsor additionally generates new share and computes all [ ] pairs on the key-path, broadcasts updated tree including only bkeys. Step 3: Every member computes the group key using .<0,0> New Intermediate Node <1,0> <1,1> New Member <2,0> M1 M2 ▇▇ ▇▇ ▇▇▇▇ ▇▇ ▇▇▇▇ ▇▇ <▇,▇> <1,0> <2,0> <2,1> <1,1> M3 Sponsor M1 M2