Supervisory control and data acquisition systems are used extensively to control and monitor critical infrastructure including power, gas, oil, and water. To integrate intelligent electronic devices in smart grid infrastructure, the utilities are deploying substation automation systems (SASs) and extensive communication networks, but there is growing concern about SCADA security including substation security. Although there are several solutions utilized to prevent security threats in SCADA networks, existing SCADA networks still have severe shortcomings. In this article, we propose a lightweight and efficient security solution for SASs that provides multilevel multi-factor authentication and attribute-based authorization by deploying public key certificates, and zero-knowledge protocol-based server-aided verification and access control mechanisms using attribute certificates. It can be seen that the proposed approach is efficient and robust.