µCLIQUES Sample Clauses

µCLIQUES. Original CLIQUES ([13]) is a CGKA protocol suite that arranges group members in a list structure (M1, . . . , Mn). The protocol specifies a role of the controller that collects contributions of other group members, adds own contribu- tion, and broadcasts information that allows all members to compute the group key. We stress that this role is tempo- rary and does not mean a trusted central authority whose existence in the group was excluded. The choice of the con- troller depends on the dynamic event and the current list

µCLIQUES. Original CLIQUES ([13]) is a CGKA protocol suite that arranges group members in a list structure (M1, . . . , Mn). The protocol specifies a role of the controller that collects contributions of other group members, adds own contribu- tion, and broadcasts information that allows all members to compute the group key. We stress that this role is tempo- rary and does not mean a trusted central authority whose existence in the group was excluded. The choice of the con- troller depends on the dynamic event and the current list structure. CLIQUES mixes unicast and broadcast commu- nication to achieve a better communication performance, since unicast communication requires less costs. Our ellip- tic curve equivalent µCLIQUES is given in Figure 2 with Mn as controller. In additive events new members are ap- pended to the end of the list. To achieve key independence the controller changes its random value r′. Last appended member becomes a controller for the next additive event. The new group key is computed in the same manner as in the setup protocol, except for the difference that the com- putation process starts from the controller’s position in the list. In subtractive events the set of leaving members L is • 1 ≤ i ≤ n − 2: Mi selects random ri ∈R {1, . . . , t − 1}, and unicasts Zi = riZi−1 to Mi+1 . (note, Z1 = r1G) • Mn−1 selects random rn−1 ∈R {1, . . . , t − 1}, and broad- casts Zn−1 = rn−1 Zn−2 . • Mi sends Xx = Zn−1 /ri to Mn. • Mn broadcasts S = {Si = rnXi|1 ≤ i ≤ n}. Mi computes K = riSi = r1r2 . . . rnG with Si ∈ S. Figure 2. µCLIQUES Setup i deleted from the list. The controller that is the most recent remaining member chooses new random value r′ and com- putes S′ = {S′ = r′Si|1 ≤ i ≤ n ∧ i /∈ L}. Upon receiv- ing S′ other members compute the new group key as in the last step of the setup protocol. If the controller is a leaving member then any other member can take over its role, as- suming it has saved the previous set S. (µ)CLIQUES do not provide verifiable trust relationship, because no other mem- ber can check whether values Zi or Xi forwarded by Xx, or the set S broadcasted by the controller are correctly built.