Abstract-In the smart grid, an integrated distributed authentication protocol is needed to not only securely manage the system but also efficiently authenticate many different entities for the communications. In addition, a lightweight authentication protocol is required to handle frequent authentications among billions of devices. Unfortunately, in the literature, there is no such integrated protocol that provides mutual authentication among the home environment, energy provider, gateways, and advanced metering infrastructure network. Therefore, in this paper, we propose a lightweight cloud-trusted authorities-based integrated (centrally controlled) distributed authentication protocol that provides mutual authentications among communicated entities in a distributed manner. Based on certificateless cryptosystem, our protocol is lightweight and efficient even when there are invalid requests in a batch. Security and performance analysis show that the protocol provides privacy preservation, forward secrecy, semantic security, perfect key ambiguous, and protection against identity thefts while generating lower overheads in comparison with the existing protocols. Also, the protocol is secure against man-in-the-middle attacks, redirection attacks, impersonation attacks, and denial-of-service attacks. Moreover, our protocol provides a complete resistance against flood-based denial-of-service attacks.