Nowadays,the design and construction of efficient internet of things (IoTs) has become a new strategies for improving living quality of all aspects.Emerging as one of the most significant extension of medical IoTs,wireless body area networks (WBANs) is capable of monitoring crucial physiological and behavioral information through wearable sensors,offering a new paradigm for the next-generation healthcare systems.As a matter of fact,due to the inherent open wireless communicating characteristics,data security and user privacy issues of WBANs have attracted attentions from both industry and academia.So far,lots of relevant researches emphasize on secure transmission and privacy protection.However,the computation and communication limitations for individual WBAN sensor have not been taken proper consideration.Moreover,the implementation of cloud computing infrastructure has provided WBANs with superior transmission and processing qualities.Emphasizing on the above issues,this paper construct a pairing-free authentication and sensor cooperation scheme in cloud-assisted WBANs,where most of the practical requirements for WBAN sensors could be satisfied.Our design guarantee the sensor anonymity in the whole transmission session.Note that our design offers pairing-free validation procedure followed with active sensor cooperation,which is suitable for massive sensor scenarios.The security analysis proves that our designed scheme is capable of achieving desired security properties and offer adequate resistances to the charted malicious attacks.Meanwhile,security comparison demonstrates that the proposed protocol is secure compared with the state-of-the-arts.