Protection of wireless technology-enabled e-healthcare data transfer over constrained devices of body sensor networks using lightweight security mechanisms is the demand of health sector nowadays. A new secure wireless body sensor network architecture (S-WBSN) with reduced CPU cycles and computational cost is proposed. S-WBSN uses OTP-Q (One-Time Pad-Quasi) and Diffie-Hellman key exchange algorithms for encryption and mutual authentication, respectively. To ensure mutual authentication among <WBSN, Local Processing Center (LPC)> and <WBSN, Data Server> components, the Diffie-Hellman key exchange algorithm is used. Using the S-WBSN architecture, security requirements such as mutual authentication, and privacy preservation thwarting security attacks are perfectly met comparing other security-based research works on healthcare data monitoring. The one-time pad-based quasi-group algorithm is a stream block cipher that operates on the data observed from the sensors of the WBSN. Before transmitting encrypted data, authentication is to be established. The proposed system methodology proves to be efficient and consumes fewer CPU cycles. The encryption and decryption processing times are comparatively less than the state-of-the-art approaches.