Multi-hop routing is essential to the operation of wireless ad hoc networks. Unfortunately, it is very easy for an adversary to forge or modify routing messages to inflict severe damage on the underlying routing protocol. In this paper, we present SEAR, a Secure Efficient Ad hoc Routing protocol for ad hoc networks that is mainly based on efficient symmetric cryptography, with asymmetric cryptography used only for the distribution of initial key commitments. We show, through both theoretical examination and simulations, that SEAR provides better security with significantly less overhead than other existing secure AODV protocols.