The 3rd Generation Partnership Project (3GPP) defined a new architecture, called Home eNode B (HeNB). The 3GPP has also presented a protocol for communications between HeNB and core networks for mutual authentication. To reduce the authentication costs associated with communication, computation and energy, this paper proposes a simple and low-cost re-authentication protocol that does not compromise the provided security services. The proposed protocol uses as the re-authentication parameter a Master Session Key (MSK) that has already been computed in the initial authentication, and does not require the full initial authentication to be repeated. Moreover, the proposed protocol does not modify the 3GPP infrastructure, and is easily applied to the HeNB system. Finally, the security of the proposed protocol is verified by Automated Validation of Internet Security Protocols and Applications (AVISPA) and Burrows-Abadi-Needham (BAN) Logic; detailed evaluations of performance are also given. The analysis results illustrate that the proposed protocol can achieve at least 50% cost reduction in communication and 58% cost reduction in energy. The computational cost is also reduced by half compared with the initial authentication.