## 1 Introduction  
Traditionally, Message Queuing Telemetry Transport (MQTT) has been the most widely used communication protocol in IoT. Its purpose is to send and receive messages over a narrow bandwidth and with low power consumption. Currently, information interaction through the broker adopts the publish/subscribe method. The current process is to register the model to reduce the conversion time of message processing. All subscribers or senders are not encrypted by default after registration. When data are transmitted in the IoT device endpoint, the publisher is activated to send a message to the broadcast station, and other IoT nodes receive it by subscription. However, the MQTT protocol encrypted by TLS (Transport Layer Security) on port 8883 needs to be improved. Messages are encrypted in transit but require TLS credentials that are updated on the fly to ensure confidentiality. In the conventional communication protocol, nodes uphold persistent connectivity with the transmitting station, primarily executing the registration operation during connection establishment. Notably, the payload of the packet remains unencrypted throughout the communication process. Instead, the security measures especially entail TLS-based encrypted connections, alleviating potential confidentiality concerns. However, while TLS can construct a secure transmission protocol in the same broadcast network environment [1], there is no way to prevent other nodes in the same broadcast network environment from exchanging data using the same security certificate. Therefore, the combination of MQTT and TLS [2] must be improved for IoT to perform message management operations under the same broker.  
Therefore, how do we set up a system under an exact broadcast communication mechanism and ensure all the receivers can be under the exact broadcast communication mechanism and still carry out distributed transmission based on different encryption keys? Can we solve the grouping problem effectively, or is it a reliability mechanism on the off-load? The Internet of Things (IoT) ecosystem includes numerous interconnected nodes. In addition to facilitating data exchange between individual nodes, the research explores the potential formation of distinct clusters, each housing specific nodes. To facilitate this, multiple tags are used for grouping purposes. Tagging allows nodes to seamlessly join or leave clusters without compromising the encrypted integrity of Lianxun messages transmitted between individual nodes and the broadcast center. When the broker sends a message to the subscriber, because the message itself is exchanged and transmitted through the bound key, the unauthorized nodes cannot read and modify the data. This research uses an innovative architecture to propose a message transmission method to improve the communication security of the Internet of Things. Previous research has solved the problem of packet message security, but our study adds a blockchain encryption method, an innovative technological development. In the past, we reviewed relevant research on the IoT data transmission process, which mainly focused on encrypting data during the transmission process through TLS. Therefore, we found that if we can combine the encryption of the blockchain through the broadcast method, converting the key into a one-to-one and a pair-to-group method to encrypt the data transmission time, respectively, it can improve this problem and solve the technical limitation, as long as the broker can be registered to receive and decrypt broadcast packets. The information security issues of cross-encoding messaging led us to initiate further research on this topic. In this study, the background knowledge and relevant literature will be discussed in the Section 2, the experimental environment design will be constructed in the Section 3, the data analysis and discussion of the experimental results will be provided in the Section 4, and the research conclusions and contributions will be described in the Section 5.