STR Protocol Clause Samples

STR Protocol. STR is basically an “extreme” version of TGDH, where the key tree structure is completely imbalanced or stretched out. This protocol and its features are described in details (▇▇▇▇▇ et al.,1998; ▇▇▇ et al, 2001). Like TGDH, the STR protocol uses a tree structure that associates the leaves with individual random session contributions of the group members. Every internal (non-leaf) node has an associated secret key and a public blinded key. The secret key is the result of a ▇▇▇▇▇▇-▇▇▇▇▇▇▇ key agreement between the node’s two children. The group key is the key associated with the root node. ▇▇▇ uses a key tree to manage the key group. The tree has two types of nodes, namely leaf and internal nodes. Each specific group member Mi is associated with a leaf node LNi, while an internal node INi has two children: the left child INi−1, and the right child LNi. Each leaf node LNi generates randomly a session random si which should be kept secretly, and computes the corresponding blinded session random bri = gsi. An internal node INi has a secret key ki and the corresponding public blinded key bki = gki. The difference is that ki is not randomly chosen, but the result of a two-party DH key exchange between its two children: (2.1) The internal node with the greatest index is considered to be the root. The secret key of the root is the shared group key. For a group of n members, the root is INn, and the group key kn can be recursively computed using Equation 2.1. If n = 4, its group key is K = gs4∙gs3∙gs2s1 mod p. Looking at the STR key tree with n members in Figure 2.10, the member Mc, 1 ≤ i ≤ n, must know its own session random, all blinded keys and blinded session random, and keys of the path from its parent node to root node. More formally, it must store sc, bri, bki for i = 1, · · · , n (br1 = bk1), and ki for i = c, · · · , n. The rest of this section describes how STR deals with the group operations INn kn-1, bkn-1 sn, brn LNn/Mn IN2 k2, bk2 s1/k1, br1/bk1 s2, br2 sn-1, brn-1 LNn-1/Mn-1 LN1/M1 LN2/M2