User Leave: Protocol LP1 Clause Samples

User Leave: Protocol LP1 łG łG łG \ L L łG 1. Uc picks a new random rc' ∈ [1, N ] and computes zc' = grc' mod N . Using rc' , zc' and the saved set Z, Uc then proceeds exactly as in IKA1, except that it broadcasts mc = łGn zc zc' T σc where zc is the random exponential from the previous controller. 2. Upon receiving the broadcast message mc, each Ui Uc verifies that: (1) V(łGn zc zc' T , σc, PKc) = 1 and (2) the received zc is equal to the one that is received in the previous session. All users in łGn then compute their session key as K = H(T Y ) and update the set Z. We assume that in the previous example, a set of users L = {U2, U4} leaves the multicast group łGp = {U1, U2, . . . , U5} and hence the remaining users form a new multicast group łGn = {U1, U3, U5}. Also assume that U5 remains as the controller in the new multicast group łGn. Then U5 chooses a new random value r5' , and broadcasts z5, z5' = gr5' , and = gr5' (r3+r5' ), gr5' (r1+r5' ) . All users in n compute the same key: K = ( Y ), where Y = gr5' (r1+r3+r5' ).