Many applications that make use of sensor networks require secure communication. Because asymmetric-key solutions are difficult to implement in such a resource-constrained environment, symmetric-key methods coupled with a priori key distribution schemes have been proposed to achieve the goals of data secrecy and integrity. These approaches typically assume that all sensors are similar in terms of capabilities, and hence deploy the same number of keys in all sensors in a network to provide the aforementioned protections. In this paper we demonstrate that a probabilistic unbalanced distribution of keys throughout the network that leverages the existence of a small percentage of more capable sensor nodes can not only provide an equal level of security but also reduce the consequences of node compromise. We demonstrate the effectiveness of this approach on small networks using a variety of trust models and then demonstrate the application of this method to very large systems. The approach and analysis presented in this paper can be applied to all protocols that use probabilistic keys including those that employ broadcast mechanisms, hash functions or polynomials for the generation of keys.