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During the past decade,rapid advances in wireless communication technologies have made it possible for users to access desired services using hand-held devices.Service providers have hosted multiple servers to ensure seamless online services to end-users.To ensure the security of this online communication,researchers have proposed several multi-server authentication schemes incorporating various cryptographic primitives.Due to the low power and computational capacities of mobile devices,the hash-based multi-server authenticated key agreement schemes with offline Registration Server (RS) are the most efficient choice.Recently,Kumar-Om presented such a scheme and proved its security against all renowned attacks.However,we find that their scheme bears an incorrect login phase,and is unsafe to the trace attack,the Session-Specific Temporary Information Attack (SSTIA),and the Key Compromise Impersonation Attack (KCIA).In fact,all of the existing multi-server authen-tication schemes (hash-based with offline RS) do not withstand KCIA.To deal with this situation,we propose an improved hash-based multi-server authentication scheme (with offline RS).We analyze the security of the proposed scheme under the random oracle model and use the “Automated Validation of Internet Security Protocols and Applications” (AVISPA) tool.The comparative analysis of communication overhead and computational complexity metrics shows the efficiency of the proposed scheme.