Establishment of conference keys in heterogeneous networks
In order to secure communication amongst members of a conference, a secret shared by all group members must be established. The Diffie-Hellman problem is often the basis for generating keys in two-party communication, and can also be used to establish conference keys. In heterogeneous networks, many conferences have participants of varying computational power and resources. Most conference keying schemes do not address this concern and place the same burden upon less-powerful clients as more-powerful ones. The establishment of conference keys should try to minimize the burden placed on more resource-limited users while ensuring that the entire group can establish the group secret. In this paper, we present a scheme for establishing a conference key using the two-party Diffie-Hellman scheme. The scheme is hierarchical, forming subgroup keys for successively larger subgroups en route to establishing the group key. A full, binary tree called the conference tree governs the order in which subgroup keys are formed. Key establishment schemes that consider users with varying costs or budgets are designed by appropriately choosing the conference tree. The tree that minimizes the total group cost is produced via the Huffman algorithm. A criterion is presented for the existence of a conference tree when users have varying budgets, and a greedy algorithm is presented that minimizes the total length of the conference tree under budget constraints.