Wireless sensor networks (WSNs) face significant challenges in terms of energy efficiency and security due to the limited energy capacity of sensor nodes and the sensitivity of the data they collect. This paper proposes an energy-efficient clustering and secure communication protocol for WSNs. The protocol includes an efficient cluster head (CH) selection scheme that employs backup CHs and a suitable CH handover threshold to reduce network energy consumption. Additionally, a pairing-free identity-based digital signature (PFIBDS) algorithm based on elliptic curve cryptography (ECC) is implemented to ensure secure communication between CH and base station (BS) and CH and sensor nodes (SN). The proposed protocol is evaluated through simulations using MATLAB and compared against modified versions of existing protocols. The simulation results show that the proposed protocol outperforms the modified EECSM protocol in terms of network lifetime by 86.55% when the CH handover threshold is set to 40%. An optimal CH handover threshold of 60% is identified to balance prolonging network lifetime and achieving satisfactory average residual energy. Overall, the proposed protocol offers an effective solution for energy-efficient clustering and secure communication in WSNs.