Focusing on the problem that user privileges cannot dynamically change with time in the current access control and the security problems in the access control contract, an access control model based on Role-Based Access Control (RBAC) model, blockchain and user credit was proposed. Firstly, the roles were distributed to relevant users by the role publishing organization, and the access control strategy was stored in the blockchain through smart contract method. In the contract, the access credit threshold was set, and the contract information was verifiable, traceable and tamper-proof to any service provider organization in the system. Secondly, the final credit was evaluated by the model according to current credit, historical credit and recommended credit of the user, and the access privileges of the corresponding role was obtained based on the final credit. Finally, when the user credit reached the credit threshold set in the contract, the user can access the corresponding service organization. Experimental results show that the proposed model has certain fine granularity, dynamicity and security in the security access control.

Focused on the large user's decryption overhead of the Ciphertext Policy Attribute-Based Encryption (CP-ABE) access control scheme in cloud storage, a CP-ABE Access Control Scheme Based on Proxy Re-Encryption (CP-ABE-BPRE) was proposed, and the key generation method was improved. Five components were included in this scheme:trusted key authority, data owner, cloud service provider, proxy decryption server and data visitor. The cloud server re-encrypted the data, and the proxy decryption server performed most of the decryption calculation. The proposed scheme reduces the user's decryption overhead effectively,and solves the data leakage problem caused by illegal stealing of the user's private key in the traditional CP-ABE scheme, and the direct revocation of user attributes is provided while the fine-grained access control is ensured in the scheme. A comparison with other CP-ABE schemes demonstrates that this scheme has better decryption performance for users when accessing cloud data.

Focusing on the problems of high energy consumption, low efficiency and poor scalability of Practical Byzantine Fault Tolerance (PBFT) consensus algorithm, Dynamic authorized Byzantine Fault Tolerance (DDBFT) consensus algorithm and Consortium Byzantine Fault Tolerance (CBFT) consensus algorithm existed in the blockchain, Practical Byzantine Fault Tolerant consensus algorithm based on Voting (VPBFT) was proposed by introducing voting mechanism. Firstly, based on PBFT algorithm, the nodes in the network were divided into four types of nodes with different responsibility. Secondly, the voting nodes in the algorithm had voting and scoring rights to supervise the production nodes to produce data blocks honestly and reliably, the production nodes producing valid data blocks had priority to be selected into next turn, while the candidate nodes were able to be voted as production nodes, and the ordinary nodes were able to be voted as production nodes or candidate nodes. Finally, different types of nodes had a certain quantity relationship between themselves, which means the parameters were able to be dynamically adjusted when the number of different types of nodes or the total number of nodes in the network changed, so that the algorithm was able to adapt to the dynamic network. Through performance simulation analysis, the proposed VPBFT algorithm has low energy consumption, short delay, high fault tolerance and high dynamicity compared with consensus algorithms such as PBFT, DDBFT and CBFT.