Internet of Things (IoT) utilizes an intelligent technique to facilitate the design and development of smart-urban projects. As the smart devices have limited battery sources, IoT services should initiate its setup with low-power consumption. Most of the existing approaches use Long Range Wide Area Network (LoRa-WAN) as a media access layer. It provides a long-range communication between the smart devices and application systems over Low Power Wide Area Network (LP-WAN). However, it fails to achieve end-to-end security and perfect secrecy to guarantee access security of the channels. An objective of mobile-sink is to solve the problem of data confidentiality, mutual authentication, session-key agreement, and preventing potential attacks. Thus, this paper presents a lightweight based authentication and key management (L-AKM) scheme for Smart IoT-Assisted Systems. To accomplish the key objectives of L-AKM, a lightweight continuous authentication was preferred that adopts the valid authentication period and continuous user authentication session to speed up the authentication process. The performance analysis proves that the L-AKM scheme achieves better security efficiencies to resist various potential attacks such as forgery, replay, password guessing, etc. However, the experimental analysis shows that the proposed L-AKM consumes more transmission delay and throughput rate due to extra authentication phases. © 2020 Elsevier Ltd