As various applications of wireless ad hoc network have been proposed, security has become one of the big research challenges and is receiving increasing attention. In this paper, we propose a distributed key management and authentication approach by deploying the recently developed concepts of identity-based cryptography and threshold secret sharing. Without any assumption of prefixed trust relationship between nodes, the ad hoc network works in a self-organizing way to provide the key generation and key management service, which effectively solves the problem of single point of failure in the traditional public key infrastructure (PKI)-supported system. The identity-based cryptography mechanism is applied here not only to provide end-to-end authenticity and confidentiality, but also to save network bandwidth and computational power of wireless nodes.