A smart-metering system is a system that meters electricity, gas, and water consumption and manages their supply by controlling measuring devices remotely. Power-line communication (PLC) does not require a separate communication line and can be easily installed by utilizing power-line infrastructure. PLC also allows users to easily connect measuring devices to the PLC network by plugging the power cord into an electrical outlet. Therefore, a smart-metering system over PLC has been considered as one of the most appropriate technologies for meter reading and automatic control, which are essential in realization of a smart grid. We propose a secure smart-metering protocol including: 1) key materials generation and provisioning to devices without exposure; 2) initialization to authenticate devices in the network and share keys between devices before exchanging data, (3) secure transmission of meter-reading data, and 4) revocation management to handle discarded devices from the network. Especially, our protocol provides strong authentication of devices and data: It prevents a single point of failure by adopting secret sharing through multiple certificate authorities. It also reduces the risk of denial-of-service attacks on the server by hop-by-hop authentication for data transmitted from terminal nodes to the server.