The 5G Internet of vehicles (IoV) enables high-speed data transmission by applying 5G technology to vehicular networks. However, with the rapid growth in the number of vehicles, traditional single third-party key generation can lead to single-point failures. In addition, wireless communication faces risks such as message interception, tampering, and network disruption due to a large number of untrustworthy false messages. To address these issues, this study proposes a blockchain-based semi-distributed message authentication and encryption scheme. First, a semi-distributed key generation and distributed information-sharing framework based on a consortium blockchain is designed. The 5G base stations provide full network coverage, while regional vehicle management centers act as full nodes to maintain the blockchain’s proper operation, and vehicles, as lightweight nodes, can only view the information stored on the blockchain. Second, to ensure message source authentication and confidentiality, a certificateless signature algorithm without bilinear pairing is designed, and an inverse hash chain is employed to generate reputation tokens for message encryption and decryption. To address the problem of untrustworthy false messages, a reputation-based system is introduced, where disseminating false messages leads to a decline in the vehicle’s reputation value. This mechanism helps to constrain vehicle behavior and reduces the number of false messages at the source. Finally, security analysis and experimental results demonstrate that the proposed scheme ensures communication security, effectively mitigates single-point failure risks through semi-distributed key acquisition, and prevents tampering, replay, and impersonation attacks. Moreover, the proposed scheme incurs low computational and communication overhead, meets the real-time requirements of IoV, and incurs low Gas costs for executing reputation update contracts, further demonstrating the practicality and feasibility of the proposed scheme.