Our research addressed the problem of securing multicast communications in an energy-constrained ad-hoc network environment. Existing efficient key distribution schemes for wired networks that rely on logical hierarchies are extremely energy inefficient for energy-constrained wireless ad-hoc networks. The joint consideration of routing and physical layer algorithms is critical for developing energy-efficient key distribution schemes. By formulating the problem we showed that the solution is hard to compute. We overcame this problem by developing greedy, routing-aware key-distribution algorithms that are easy to compute.