Recent results indicate scalability problems for flat ad hoc networks. To address the issue of scalability, self-organizing hierarchical ad hoc architectures are being investigated. In this paper, we explore the task of providing data and entity authentication for hierarchical ad hoc sensor networks. Our sensor network consists of three tiers of devices with varying levels of computational and communication capabilities. Our lowest tier consists of compute-constrained sensors that are unable to perform public key cryptography. To address this resource constraint, we present a new type of certificate, called a TESLA certificate, that can be used by low-powered nodes to perform entity authentication. Our framework authenticates incoming nodes, maintains trust relationships during topology changes through an efficient handoff scheme, and provides data origin authentication for sensor data. Further, our framework assigns authentication tasks to nodes according to their computational r...