ABSTACTAd hoc networks, such as sensor and mobile ad hoc networks, must overcome a myriad of security challenges to realize their potential in both civil and military applications. Typically, ad hoc networks are deployed in un-trusted environments. Consequently, authentication is a precursor to any secure interactions in these networks. Recently, numerous authentication protocols have been proposed for ad hoc networks. To date, there is no common framework to evaluate these protocols. Towards developing such a framework, this paper proposes a generic authentication process and a new taxonomy that clarifies similarities and differences among authentication protocols reported in the literature. The taxonomy is based upon the role of nodes in the authentication function, establishment of credentials, and type of credentials. We also motivate the need for an authentication management architecture and discuss some open research issues.