Research On Attribute-based Encryption Schemes With Traceability And Revocation

With the development of cloud computing,more and more users or enterprises choose to pay for cloud storage and computing services to save local resources.As a “one-to-many” cryptosystem,attribute-based encryption can achieve fine-grained access control and data sharing.Thus it is considered to be one of the most suitable encryption systems in cloud computing environment.However,there are still many challenges in the process of its application to the cloud computing.In the encryption system,there are always some problems that malicious authority and users abuse keys.In this case,it is necessary to achieve these functionalities,such as the accountability of the malicious authority and users,the revocation of malicious users' decryption rights.In addition,since shared data is outsourced to the remote server,users can not control directly the data.Therefore,it is imperative to verify the integrity of the data.Simultaneously,the large universe can ensure the public parameters will not change with the number of attributes and support exponential attributes space.The large universe is an important functionality in the attribute-based encryption.To solve the above problems,the main works of this paper are as follows:1.A large universe revocable ciphertext-policy attribute-based encryption scheme is proposed with public auditing.The new scheme makes advantage of extended proxy-assisted approach and appending redundancy approach to weaken the users' trust of the cloud server.At the same time,an auditor is introduced to periodically check the integrity of data stored in the cloud.Since our scheme supports large universe,the number of attributes is not determined at system setup.Based on the q-type assumption,the new scheme is proved to be secure against chosen-plaintext attack in the standard model.Compared with some existing revocation schemes,the proposed scheme can achieve data integrity verification and improve revocation efficiency.Furthermore,it features lightweight computation at the user side such that users can use resource-constrained devices to access cloud data.2.An accountable large universe ciphertext-policy attribute-based encryption scheme is proposed with user revocation.The new scheme uses a “fixed point” as the identifier of the key owner to realize the traitor tracing.The proposal system can achieve revocation mechanism and forward/backward security by utilizing complete subset scheme and self-update encryption scheme.Furthermore,there is almost no additional storage of traceability by making advantage of a Paillier-style encryption.In addition,the proposed scheme can solve two problems of key abuse: illegal key sharing problem of the users and illegal key distribution problem of the semi-trusted authority.Based on the q-type assumption,the proposed system is proved to be secure against chosen-plaintext attack in the standard model.