In-motion inductive charging, or dynamic charging, is an emerging technology that allows electric vehicles (EVs) to be charged while on the move. Accurate billing for dynamic EV charging requires secure communication between the EVs and the utility, and could potentially require the secure delivery of small messages from the EVs to the utility at a very high rate, which is infeasible with the currently available solutions. In this paper we propose Fast Authentication for Dynamic EV Charging (FADEC) designed to meet the communication needs of in-motion inductive EV charging. FADEC features fast signing and verification, low communication overhead, and fast hand-off authentication to support EV mobility. Our simulations show that compared with ECDSA mandated by 802.11p standard, FADEC reduces data delivery delay by up to 97%, increases the data delivery ratio by more than an order of magnitude and enables timely data delivery even in a resource constrained environment.