# A Classification-Based Blockchain Architecture for Smart Home with Hierarchical PoW Mechanism
###### Abstract  
Smart home, as a typical Internet of Things (IoT) application, provides people with a variety of conveniences. Unfortunately, it may suffer from security and privacy issues. Currently, blockchain theory is considered as one of the potential solutions to the IoT security problem. However, according to the rules of blockchain, it requires large storage to store distributed ledgers and undertakes long latency caused by proof of work (PoW), which cannot be performed by resource-constrained IoT devices. To address the issue, we propose a classification-based blockchain architecture with a hierarchical PoW mechanism, which can reduce the storage consumption and decrease the latency. In our architecture, we divide IoT devices into several child nodes by data classification and convert the data storage into partial network storage. Furthermore, we try to set the moderate-cost security grades (SG) to adjust the difficulty of PoW for reduction of latency. Finally, comparing the performance of our scheme with the traditional method and current technology, the proposed architecture not only takes up less storage (i.e., almost 90% reduction) but also increases efficiency (i.e., almost 50% running time saving) while ensuring safety. s +
Footnote †: journal: Applied Topics in Applied Cryptology  
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Footnote 1: email: {1,2,3,4,5,6,7,8,9,10,11  
through the distributed record preservation and verification system. Currently, blockchain-based technology is widely used in various fields, such as smart education [18], smart healthcare [19], smart home [12], etc. Recently, there has been much research regarding secure IoT systems [20; 21; 22; 23]. [PERSON] et al. [24] propose a blockchain-based architecture for IoT devices that supports security and privacy. However, it is not fully built on a distributed architecture due to the use of a central cloud storage. Furthermore, they try to reduce the latency by removing the PoW consensus mechanism, but cannot prove whether it would withstand attacks performed by compromised nodes [25]. Similarly, to eliminate the PoW mechanism, a blockchain-enabled architecture of software-defined networking (SDN) controllers using a cluster structure with a new routing protocol is proposed for resource-constrained IoT device scenarios [26]. It actually uses public and private blockchains for peer to peer (P2P) communication between IoT devices and SDN controllers. In order to improve the architecture (or features, e.g., structure, verification, storage) of the original blockchain, as shown in Table 1, [PERSON] et al. [27] propose a hypergraph-based blockchain model to reduce data storage, but cannot deal with the long latency caused by PoW. [PERSON] et al. [28] develop an integrated blockchain model that includes a lightweight consensus algorithm, certificateless cryptography, and distributed throughput management scheme. It generates an overlay network to assign higher resources to a public blockchain to guarantee the dedicated security and privacy. But this scheme seems a bit complex for smart home scenarios. We can see the existing blockchain-based architecture for smart home devices face the challenge of imbalanced security and efficiency [29]. It exposes the traditional highly centralized architecture to huge security risks and vulnerabilities. Therefore, it is necessary to design a decentralized, safe, and efficient blockchain-based smart home architecture for human living. In this paper, we propose a classification-based blockchain architecture for smart homes with a hierarchy-based PoW mechanism. In our architecture, we focus on reducing storage for IoT devices while decreasing the latency caused by PoW in the condition of acceptable security risks. The major contributions of this paper can be summarized as follows. * To replace the high-risk centralized frameworks, we propose a classification-based blockchain architecture for smart homes that stores data in a fully decentralized way.