It is well established that the efficiency, safety, flexibility, and reliability of the power grid is improved by utilization of information and communication technology (ICT) in smart grid. Nevertheless, the use of ICT introduces serious challenges regarding security issues, which has led to introducing many protocols for securing the communication between the smart meters and neighborhood gateways in recent years. However, providing functional and security features such as two-way communication and resistance against memory attack, alongside the lightweight design is the ultimate goal of these schemes. To overcome all the mentioned problems, this paper proposes a super-lightweight secure protocol based on only one-way hash functions and XOR operation, which provides two-way communication and secure one-time pad key for each data transmission. The security and performance analysis shows that not only does the proposed scheme resist the existing attacks but also it dramatically improves the efficiency in terms of storage burden and computational cost.