This document summarizes and reviews several existing approaches for message authentication and source privacy in wireless sensor networks (WSNs). It proposes a new flexible authentication scheme based on elliptic curve cryptography that allows nodes to transmit an unlimited number of messages without hitting the threshold limit of previous polynomial-based approaches. Through both theoretical analysis and simulation results, the proposed scheme is shown to be more efficient than polynomial-based methods in terms of computational and communication overhead under the same security levels, while also providing message source anonymity.