<p>Smart Grid integrates data from distributed devices through data aggregation. However, during this process, leaking user electricity consumption data can pose potential risks to users. Currently, the construction of smart grid data aggregation schemes with privacy protection features uses mainly cryptographic methods, among which homomorphic encryption is a commonly used method. However, traditional homomorphic encryption schemes are constructed with single key, which means that in a distributed scenario, decryption requires all users to share the decryption key, which obviously leads to a huge risk of key leakage. In addition, the existing mainstream schemes also suffer from deficiencies in data integrity, immutability, and computational overhead. To address these challenges, we propose an efficient and secure privacy-preserving data aggregation scheme based on multi-key homomorphic encryption and blockchain (DA-MHEB). Specifically, we propose a three-layer system architecture that combines fog computing and blockchain technology in a cloud environment. Based on the distributed dual-trapdoor public key cryptosystem, we design an aggregation algorithm suitable for this architecture that supports multi-key homomorphic encryption. During the decryption process, the Chinese Remainder Theorem is used to avoid private key leakage. Additionally, the aggregated electricity data is recorded on the blockchain to ensure the integrity and immutability of the data. Detailed security proofs show that DA-MHEB meets the requirements for security and privacy protection. The experimental results indicate that DA-MHEB is practically applicable in terms of performance.</p>