The recently emerging advanced metering infrastructure (AMI) is envisioned to be one of the most prominent features of the smart grid. Security, especially authentication, is crucial for the success of large‐scale AMI deployment. Unfortunately, authentication schemes relying on per‐packet signature and per‐signature verification introduce heavy cost for computation and communication. Due to resource constraints, smart meter authentication requirements cannot be satisfied by this scheme. In this chapter, a new authentication architecture for AMI is described to validate the delay‐tolerant metering data. In this chapter, not only a set of efficient authentication schemes, but more importantly, their corresponding fault diagnosis algorithms will be recited. The authentication scheme incurs substantially lighter overheads than those by the existing schemes, while it can effectively address the formidable authentication challenges in AMI.