Consider a communication network where each process needs to securely exchange messages with its neighboring processes. In this network, each sent message is encrypted using one or more symmetric keys that are shared only between two processes: the process that sends the message and the neighboring process that receives the message. A straightforward scheme for assigning symmetric keys to the different processes in such a network is to assign each process O ( d ) keys, where d is the maximum number of neighbors of any process in the network. In this article, we present a more efficient scheme for assigning symmetric keys to the different processes in a communication network. This scheme, which is referred to as logarithmic keying, assigns O (log d ) symmetric keys to each process in the network. We show that logarithmic keying can be used in rich classes of communication networks that include star networks, acyclic networks, limited-cycle networks, planar networks, and dense bipartite networks. In addition, we present a construction that utilizes efficient keying schemes for general bipartite networks to construct efficient keying schemes for general networks.