Balanced batch LKH: new proposal, implementation and performance evaluation

Perfect secrecy can only be achieved in multicast groups by ciphering data sent to the group with a different key every time a member joins or leaves the group. A key server must send the new key to all the remaining members so bandwidth efficiency concerns appear. Logical key tree algorithms reduce the number of messages to be sent, but in many scenarios, rekeying after each membership change has no sense. Batch rekeying algorithms are proposed as a solution to these problems. However such methods need to maintain the logical key tree balanced all the time on order to achieve maximum bandwidth efficiency. This paper presents a new technique for multicast batch rekeying. This technique reallocates the tree nodes in order to keep the tree balanced all the time.