Scaling the Blockchain-based Access Control Framework for IoT via Sharding

Access control is one of the important means to protect privacy in the Internet of Things (IoT), and access control model is mostly based on central trusted entity. The decentralized blockchain technology makes up for the shortcomings of the existing access control model for IoT. However, the transaction generation rate in IoT has brought huge challenges to the scalability of the integration framework of blockchain and IoT, including the Transaction Processing Speed (TPS) and the storage of each node.This paper proposes the Network Sharding Scheme (NsScheme) to improve the scalability of the blockchain-based access control framework in IoT. Based on the three-tier architecture of "cloud-edge-device" in IoT, we divide edge nodes into several shards. Each shard maintains a local blockchain, and cloud nodes maintain a global blockchain. Multiple blockchains process transactions in parallel to improve the Transaction Processing Speed (TPS) and reduce the storage of each node. In the meantime, we present the transactions allocation scheme that which shard processing the transaction depends on both parties in transaction, which can reduce the routing cost of querying transactions to O(1). Considering that the number of cross-shard transactions will affect the query cost of cross-shard transactions, we further introduce the network sharding algorithm based on Access Frequency Set (AFS) between nodes, which can effectively reduce the query cost of cross-shard transactions. The simulation results indicate that with the increase of the number of shards, NsScheme can linearly increase the TPS and reduce the storage of each node.