Since its birth more than two decades ago, public key cryptography has been recognized as one of the most effective mechanisms for providing fundamental security services including authentication, digital signatures and encryption for dynamic networks. Effective management of keys, or digital certificates holding the keys, is one of the key factors for the successful wide-spread deployment of public key cryptography. The public key infrastructure (PKI ), an infrastructure for managing digital certificates, was introduced for this purpose. The most important component of PKI is the certificate authority (CA), the trusted entity in the system that vouches for the validity of digital certificates. This work describes a framework to provide efficient yet effective distributed CA service for ad hoc wireless networks. We select physically or computationally more secure nodes as MOCAs (MObile Certificate Authority) and use threshold cryptography to distribute the CA's private key among these MOCA nodes. We also provide a protocol for clients to contact MOCAs and get certification services without incurring excessive overhead.