The development of the applications of Internet of Things (IoT) technology continues to grow steadily-one of the top applications being smart home environments. A smart home comprises digital devices and systems that operate inside a home to bring efficiency to home life. Devices with low computational ability and devices with high computational ability work together in a smart home network, and therefore, communication between devices needs to be secure. This article considers a lightweight and secure session-key establishment scheme for smart home networks and incorporates the Diffie-Hellman (DH) key exchange as an alternative method. A trusted service provider provides the algorithm parameters to the devices so that a public key can be established between the home gateway and a smart device. The proposed scheme is formally analyzed using Security Protocol Animator for Automated Validation of Internet Security Protocol and Applications (AVISPA).