Abstract: The rapid proliferation of wearable devices， coupled with the continuous evolution of the sixth generation mobile communication technology （6G）， has propelled Internet of Things applications into a new phase of development. In this context， remote healthcare information systems have emerged as a critical foundational service， enabling the storage and management of patients’ sensitive data on remote medical servers while supporting interactions with authorized entities over public networks. However， the inherent vulnerability of the public internet exposes such systems to a wide spectrum of security threats， including malicious attacks and privacy leakage. Consequently， the design of robust authentication and key-agreement mechanisms has become indispensable for safeguarding these mission-critical services. During key agreement， participating entities exchange ephemeral keying materials over public channels to establish a shared session key， which facilitates subsequent encrypted communication and ensures the confidentiality and integrity of the transmitted data. Although several representative schemes have been proposed for remote healthcare information systems， many of them incur substantial computational， communication， and energy overheads， rendering them unsuitable for resource-constrained user devices. Moreover， certain lightweight protocols fail to achieve their claimed security and functional objectives， leaving them susceptible to a variety of known attacks. To overcome these limitations， this study proposes a robust authentication protocol tailored for remote healthcare information systems. The proposed scheme leverages cryptographic hash functions to achieve mutual authentication and session-key establishment between users and medical servers. By minimizing computational operations， the protocol enhances efficiency without compromising security. Comprehensive security analysis and performance evaluation results demonstrate that the proposed protocol effectively overcomes the limitations of the existing approaches， fully satisfies critical security and functional requirements， and achieves a well-balanced trade-off among computational cost， communication overhead， runtime overhead， and energy consumption. Therefore， it provides a practical and efficient solution for resource-constrained remote healthcare information systems.