Smart meters have become the essential elements of smart city applications, where smart grid (SG) environments could be enabled with the real-time monitoring and collection of power usage data through trusted wireless networks. Key agreement schemes are fundamental to ensuring secure and trustworthy power usage assessment in SG systems, while also protecting data integrity and optimizing computational costs. This paper proposes an Authentic Key Agreement (AKA) scheme based on Blockchain designed to enhance the security, integrity, and efficiency of SG systems. The proposed scheme utilizes the Advanced Encryption Standard (AES) cryptographic 
algorithm integrated with Blockchain technology, achieving better security and computational efficiency compared to existing state-of-the-art schemes. Simulation results obtained using the NS3 simulator demonstrate a significant reduction in network delay. Specifically, when the number of nodes in a network cluster is doubled, the proposed framework achieves a 25% reduction in delay. Thus, this proposed framework offers increased efficiency, improved security, lower costs, and better transparency of power usage in SGs.