Internet of Things (IoT) networks have spread to many important fields and applications. The security of these networks remains a big challenge due to their unique characteristics and delicate operations. The blockchain has recently been proposed as a system to secure IoT data and communications. However, the blockchain demands a heavy load that cannot be handled by light IoT devices. For this reason, a large number of “lightweight blockchain” solutions were proposed that aim to modify the blockchain structure and characteristics to make it suitable for IoT networks. In this paper, we propose a novel and unique blockchain system for IoT networks that is based on four lightweight features: “lightweight architecture”, “lightweight authentication”, “lightweight consensus”, and “lightweight storage”. While previous research works focused on one or two of these features, we propose a system that combines the four features into a comprehensive lightweight blockchain system that utilizes a “lightweight cryptography” mechanism to achieve better performance from several perspectives, such as transaction latency, block generation delay, network overhead, and resilience to attacks.