## 3 Proposed Hybrid Framework
### Framework Description  
The proposed blockchain system framework in this study is shown in Figure 4. Based on the traditional three-tier structure of the IoT, the framework adds a blockchain composite layer. The addition of the blockchain composite layer adds a buffer between the application layer and the transport layer and relieves the pressure of the application layer when facing massive data delivery. The perception layer, at the bottom of the framework, consists of IoT devices large and small and is a key part of information collection. The transport layer is a network cluster with seamless connection and all-round coverage of the IoT, and its main function is to transmit information acquired by the perception layer. The network transmission function of the transport layer overlaps with the network layer in the blockchain composite layer, which is set as a separate layer for convenient representation. The function of the application layer is information processing. The application layer, together with the lowest sensing layer, is the salient feature and core of the IoT. The application layer can calculate, process, and mine the data collected by the sensing layer, so as to realize the real-time control, accurate management, and scientific decision-making of the physical world. In the proposed hybrid framework, IoT data can be transmitted to the sensing layer via IoT protocols and then be converted into the appropriate blockchain transaction format and transmitted to other nodes through the blockchain network. Blockchain nodes can verify the legitimacy of transactions and add them to the blockchain to ensure the security and immutability of the data. This combination can provide greater security, trust, and transparency to IoT systems, while enabling data exchange and sharing across devices and platforms. In our framework, when more and more IoT devices start to connect to the system, the result is more and more data transaction information. In our design, a block can store up to 4000 transactions, each transaction can declare 500 MB of data, and each block can be up to 1 MB. This means that 1 GB of space can claim up to 1000 blocks and 500 GB of data, so our framework is able to guarantee scalability of the ability to handle an increasing number of IoT devices and transactions. It is worth mentioning that as more and more IoT devices begin to connect to the blockchain network, the processing power and stability of our system will also increase. In the blockchain composite layer, the data layer defines the data structure of the blockchain and the chain and formulates relevant standards for various information in the blockchain, such as the storage of blockchain information, Unspent Transaction Output  
Figure 4: Schematic diagram of the overall framework. We added the Blockchain Composite layer to the traditional IoT architecture, which is subdivided into a 5-layer structure. (UTXO), and Data Stored Sets (DSSs). The network layer is responsible for the access and verification of blockchain nodes (users). The consensus layer is responsible for synchronizing local blockchain, UTXO, and DSS information between nodes; verifying the legality of each packaged block; and maintaining the operation sequence and fairness of the system. The incentive layer sets up relevant rewards for users who participate in maintaining the blockchain. A smart contract is a piece of code deployed on a blockchain, where users can deploy the corresponding smart contract to realize data-related functions. It differs from the application layer in that it is a piece of code on a blockchain and can provide lightweight and decentralized services. The flow of data is based on DIDs. A DID should be issued by one or more trusted third parties, and this DID can be verified by other users and provide relevant verification services. In the blockchain system, users can be represented by public key information, which uniquely identifies a user, and this public key information is also the identity identifier of the DID decentralized identity.