Cloud computing becomes increasingly popular for data owners to outsource their data to public cloud servers while allowing intended data users to retrieve these data stored in cloud. This kind of computing model brings challenges to the security and privacy of data stored in cloud. Attribute-based encryption (ABE) technology has been used to design fine-grained access control system, which provides one good method to solve the security issues in cloud setting. However, the computation cost and ciphertext size in most ABE schemes grow with the complexity of the access policy. Outsourced ABE (OABE) with fine-grained access control system can largely reduce the computation cost for users who want to access encrypted data stored in cloud by outsourcing the heavy computation to cloud service provider (CSP). However, as the amount of encrypted files stored in cloud is becoming very huge, which will hinder efficient query processing. To deal with above problem, we present a new cryptographic primitive called attribute-based encryption scheme with outsourcing key-issuing and outsourcing decryption, which can implement keyword search function (KSF-OABE). The proposed KSF-OABE scheme is proved secure against chosen-plaintext attack (CPA). CSP performs partial decryption task delegated by data user without knowing anything about the plaintext. Moreover, the CSP can perform encrypted keyword search without knowing anything about the keywords embedded in trapdoor.

KSF-OABE: Outsourced Attribute-Based Encryption with Keyword Search Function for Cloud Storage

With the development of cloud computing, outsourcing data to cloud server attracts lots of attentions. To guarantee the security and achieve flexibly fine-grained file access control, attribute based encryption (ABE) was proposed and used in cloud storage system. However, user revocation is the primary issue in ABE schemes. In this article, we provide a ciphertext-policy attribute based encryption (CP-ABE) scheme with efficient user revocation for cloud storage system. The issue of user revocation can be solved efficiently by introducing the concept of user group. When any user leaves, the group manager will update users’ private keys except for those who have been revoked. Additionally, CP-ABE scheme has heavy computation cost, as it grows linearly with the complexity for the access structure. To reduce the computation cost, we outsource high computation load to cloud service providers without leaking file content and secret keys. Notably, our scheme can withstand collusion attack performed by revoked users cooperating with existing users. We prove the security of our scheme under the divisible computation Diffie-Hellman assumption. The result of our experiment shows computation cost for local devices is relatively low and can be constant. Our scheme is suitable for resource constrained devices.

Flexible and Fine-Grained Attribute-Based Data Storage in Cloud Computing

Outsourcing data to the cloud are beneficial for reasons of economy, scalability, and accessibility, but significant technical challenges remain. Sensitive data stored in the cloud must be protected from being read in the clear by a cloud provider that is honest-but-curious. Additionally, cloud-based data are increasingly being accessed by resource-constrained mobile devices for which the processing and communication cost must be minimized. Novel modifications to attribute-based encryption are proposed to allow authorized users access to cloud data based on the satisfaction of required attributes such that the higher computational load from cryptographic operations is assigned to the cloud provider and the total communication cost is lowered for the mobile user. Furthermore, data re-encryption may be optionally performed by the cloud provider to reduce the expense of user revocation in a mobile user environment while preserving the privacy of user data stored in the cloud. The proposed protocol has been realized on commercially popular mobile and cloud platforms to demonstrate real-world benchmarks that show the efficacy of the scheme. A simulation calibrated with the benchmark results shows the scalability potential of the scheme in the context of a realistic workload in a mobile cloud computing system.

Hybrid Attribute- and Re-Encryption-Based Key Management for Secure and Scalable Mobile Applications in Clouds

Directly revocable key-policy attribute-based encryption with verifiable ciphertext delegation

Achieving high performance and privacy-preserving query over encrypted multidimensional big metering data

Cipher text-Policy Attribute Based Encryption (CP-ABE) is a promising cryptographic primitive for fine-grained access control of shared data. However, when CP-ABE is used to control outsourced data sharing, it confronts two obstacles. Firstly, the data owner must trust the attributes authority, secondly, the issue of attribute revocation of CP-ABE schemes, which suffers from such problems as different granularities of revocation, poor scalability and high computational complexity, is cumbersome. In this paper, we propose a new CP-ABE scheme that the data owners can fully control their outsourced shared data. We also resolve the issue of revocation including the entire user access privilege and just partial access right of the user, i.e., a subset of his/her attributes. Our proposed solution can achieve minimal overload by integrating CP-ABE with the access control of system. In addition, the data owners and the attributes authority can delegate most of laborious tasks to revocation proxy severs with the technique of proxy re-encryption. Finally, we present the quantitative test and analysis on the performance of our proposed scheme.

An Efficient Attribute Based Encryption Scheme with Revocation for Outsourced Data Sharing Control

Gentry's fully homomorphic encryption scheme can only applied to single bit message, since the recrypt algorithm for full size message is relatively complicated Based on Gentry's fully homomorphic encryption scheme, we provides a improvement and present a fully homomorphic encryption scheme which can encryption on n-bit message, and the asymptotic complexity is equal to Gentry's

Han Jing-Li

Papers

An Efficient Attribute Based Encryption Scheme with Revocation for Outsourced Data Sharing Control

Fully Homomorphic Encryption Scheme Extended to Large Message Space