In a secure multicast environment, the distribution of cryptographic keys may be a primary indicator of system performance. The mathematics of public key cryptography do not scale well especially for large multi-user networks, and a symmetric-key-based system is not feasible over a network spread out geographically. The problems become even more complicated when we begin dealing with multiple levels of security, i.e. different classification levels of traffic as well as group memberships/permissions. In this paper, we present a new approach to multi-level secure multicast, one that uses the secure lock encryption scheme based on the mathematics of the Chinese Remainder Theorem to distribute keys to various subgroups. Our solution can be applied to both one-to-many and many-to-many group communications. In addition, it presents a viable solution for the distribution of one-time session keys during actual message transmission.