In recent years, wireless sensor networks are widely utilized healthcare applications, like hospital and residential patient monitoring. Wireless medical sensor networks are more vulnerable to eavesdropping, modification, impersonation and replaying attacks than the wired networks. Tons of labor has been done to secure wireless medical sensor networks. The prevailing solutions can protect the patient data during transmission but cannot stop the within attack where the administrator of the patient database reveals the sensitive patient data. During this paper, we propose a practical approach to the within attack by using multiple data servers to store patient data. The most contribution of this paper is securely distributing the patient data in multiple data servers and employing the Paillier and ElGamal cryptosystems to perform statistical analysis on the patient data without compromising the patients? privacy.Wireless medical sensor networks certainly improve patient?s quality -of-care without disturbing their comfort. However, there exist many potential security threats to the patient sensitive physiological data transmitted over the overall public channels and stored within the back-end systems.