A Research Of Efficient And Security Provable Attribute-based Encryption Scheme

With the rapid developing of the Internet and improvement of the cloud computing technology,more and more institutions and individual users choose cloud platform as their infrastructure of engineer computation and data storage.Massive data would be transferred to the cloud to be computed and stored.With the using of resources gathered by the cloud platform,users can impressively reduce the cost of hardware.However,it would encounter some security problems.Considering the public cloud platform belonging to the public resources,it is open to all users.How to offer the secure and stable data transformation,storage,accessing,sharing service under the complex cloud environment with multiple users is a significant problem,because the security of user data is not ignorable.Traditional cryptography can not handle the above problem effectively.And a new proposed security notion in recent years,called Attribute Based Encryption(ABE),is deeply explored and can handle that security problem.Owing to the flexible access control policy and stable security provided by the ABE scheme,ABE has become the hotspot in the field of cryptography research and massive relative achievements have been reached.Because of the non-negligible computation cost during the ABE scheme,the efficiency problem becomes a bottleneck limiting the application of ABE.By analyzing some classic ABE schemes and comparing these schemes' access structures,computation complexity,length of ciphertext,efficiency of revocation,this thesis concludes some points which can be deeply researched to improve the ABE's efficiency.Such as the access structure is too complex,the computation cost is too huge,the size of ciphertext would group with the number of user's attributes and the system would periodically communicate with all system users during the revocation.This thesis researches the above problems and achieves the following results:This thesis proposes an outsourced encryption and decryption ciphertext-policy ABE scheme with constant-size ciphertexts and secret keys.This scheme combines two abilities which called outsourced encryption and decryption and the constant-size ciphertexts and secret keys.The scheme could avoid the explosion of ciphertexts size as well as it could outsource the majority computation to the third party servers.The schema could effectively reduce the burden of the storage,bandwidth and local computation.The security and efficiency analyses are proposed as well.This thesis also proposes an outsourced decryption and user revocation ciphertext-policy ABE scheme.This scheme combines the ciphertext-delegation and outsourcing technology.What's more,it implements effectively revocation by avoiding periodically interaction with the system users.It also implements the forward-security.Finally,the analyses for the scheme's security and efficiency are proposed and the application scenario,which is a thesis management system for securely manage and share theses,is discussed.