The emergence of smart grids has considerably improved the quality of life. However, the real-time electric usage information transmitted by smart meters reveals consumers' private information. Based on the remote anonymous attestation technology in trusted computing, the concept of a trusted smart meter is proposed in this paper in order to protect consumers' private information from the terminal end. Attribute certificates are used to hide the platform configuration of smart meters and the ring signature technology is adopted to hide users' personal information. The proposed protocol not only prevents the leakage of private information with competitive efficiency but also ensures trusted detection for upgrading the software of smart meters.