Abstract: With the rapid development and wide application of cloud computing technology,data security issues in the cloud environment have become the focus of users' attention.To ensure data privacy,users encrypt the private data and upload it to the cloud server.Nevertheless,it is challenging to retrieve ciphertext containing specific information from massive encrypted data of multiple cloud servers.Traditional searchable encryption schemes cannot be directly applied to ciphertext data retrieval in the multi-cloud environment.The attribute-based encryption provides a new solution for ciphertext keyword retrieval.However,the existing related schemes have some problems,such as only supporting single or conjunctive keyword retrieval,inflexible access control policy,low retrieval efficiency,large calculation and storage overhead,and not applying to the multi-cloud environment effectively.Therefore,this paper proposed an efficient Multi-keyword Retrieval scheme based on Attribute encryption in the Multi-cloud environment (MRAM).MRAM is based on the high-performance ciphertext-policy attribute-based encryption algorithm,and realizes multi-keyword ciphertext retrieval and fine-grained access control.By introducing a retrieval server,MRAM effectively supports efficient and accurate ciphertext retrieval in multi-cloud environment.Security analysis shows that MRAM can achieve important security features such as security index confidentiality,trapdoor confidentiality,and resistance to collusion attacks.The performance evaluation verifies that MRAM has lower computational overhead in the secure index generation,trapdoor generation,and retrieval stages compared with existing solutions,and the storage overhead of the secure index and trapdoor is also smaller.

Key words: Access control policy, Attribute-based encryption, Ciphertext retrieval, Multi-cloud environment, Multi-keyword retrieval