## 1 Introduction
In 2015, the authors [10] first presented an authentication protocol for distributed wireless sensor networks to satisfy important security properties such as mutual authentication, sensor anonymity and un-traceability, system scalability, and resistances to impersonation attack, replay attack and cloning attack. In 2016, the authors [9] further proposed an authentication mechanism for IoT-based healthcare system, which is based on body sensor networks consisting of lightweight and healthcare-oriented body sensors. The authors then investigated the security density and protocol efficiency via BAN logics analysis and computation cost comparison. Even though [PERSON] and [PERSON]'s authentication schemes, i.e., BSN-Care [9] and USM-IoT [10], are designed to fit the security requirements of body sensor networks and distributed wireless sensor networks, respectively, the underlying communication architectures are client-server based and client-client-server based from the point of view of authentication analysis. Unfortunately, there still exist space for improvements of these two protocols in terms of the authentication viewpoint. First, the two schemes lack session key agreement and a man-in-the-middle attack may be launched. Based on the authentication process of BSN-Care [9] and USM-IoT [10], these two proposed systems provide user login functionality without session key agreement. A man-in-the middle adversary may simply interrupt the login request and response message and pretend that it is as a legal BSN-Care server or legal client. A fake and phishing website counterfeited as a legal BSN-Care server is a possible technique to achieve a man-in-the-middle attack. Second, we find that bitwise exclusive-or module is inappropriately used in their schemes. That is, the form of \"\(M\oplus key\)\" may be more vulnerable than the form of \"\(H(M\oplus key)\)\", where \(key\) is a secret and \(M\) is a message. From this point of view, we find that there exist insecure designs of protocol messages in [PERSON] and [PERSON]'s schemes, i.e., \(N_{x}=K_{bl}\oplus N_{I}\), \(N_{x}=K_{bl}\oplus N_{S}\), \(N_{y}=K_{bl}\oplus N_{C}\). The security density is based the robustness of random number and the exclusive-or function. This design preserves the robustness resisting to only \"cipher-text only\" level attacks and we thus suggest the form of \"\(H(M\oplus key)\)\" when designing an robust authentication scheme. Third, their schemes are not secure against a location spoofing attack. Apparently, in [PERSON] and [PERSON]'s schemes legitimate but malicious cluster heads (or servers) can tell anyone that the user, authenticated at previous sessions, is now in his/her range even though the user is not there. Due to the tradeoff among network heterogeneity, system security and computation efficiency, in this paper we would like to develop a robust IoT-oriented healthcare system for body sensor networks, called the BSNCare+, which is based on improvements on the methods presented in BSN-Care and USM-IoT. The rest of this paper is organized as follows. In Section 2, we introduce the underlying IoT communication architecture of the proposed BSNCare+ system. Section 3 illustrates the details of our proposed BSNCare+ system, and Section 4 performs the security analysis and related discussions of the BSNCare+. Then, we present performance evaluations through a demo system implementation with an IoT-oriented programming platform, i.e., Raspberry PI 2. The practicability of the BSNCare+ is thus demonstrated. Finally, we provide concluding remarks in Section 6.