<p>The Internet of Things (IoT), is a network of interconnected devices that share data and information. Two or more devices can communicate with each other to deliver and receive data using the internet. Smart devices, such as sensors and grids, have rapidly developed and are now widely employed in a range of industries. There is an immediate need to develop a public key cryptography solution to secure end-to-end communication among these IoT devices because many of them rely on the unsafe web as a method of data transfer. In this paper, we propose an attack-resistant lightweight cryptographic process for device-to-network and device-to-device authentication by assigning network coordinators to each network. The proposed security solution in this research enhances protected data transfer using a secure authentication and key establishment procedure for IoT devices. For authentication and key establishment, we have implemented the Elliptic Curve Cryptography technique with the Message Digest (MD5) hash function (ECCMD). The MD5 hash function is more secure and also speeds up the working of the protocol. The effectiveness of the proposed technique in the presence of various attacks like flooding attack, sybil attack, replay attack, man-in-middle attack and key compromise impersonation attack are analysed by implementing it on the Contiki-based Cooja simulator. To validate the performance of the proposed ECCMD scheme, we have compared its results with the LECKA-IoT and ECCbAP. The outcome reveals that the proposed method requires low energy and memory during the authentication and secure key establishment process.</p>