Research On Lightweight Attribute-Based Encryption Schemes With Blockchain

Attribute-based encryption is a type of public key encryption algorithm,which is widely used in data sharing scenarios because of its fine-grained access control.However,it depends on bilinear mapping calculation which costs scale with high complexity.Furthermore,the two common lightweight attribute-based encryption schemes both have disadvantages.Offline/online encryption can’t reduce the burden of the decryptor,and the encryptor still needs to complete all calculations in two phases.The problem of outsourced decryption is that verification of ciphertext is difficult to solve.In addition,as the core component of ABE,access structure has many forms of expression,and the choice of access structure will affect the logical expression ability of the algorithm.For example,tree access structure and linear secret sharing scheme cannot express logic of ‘NOT’.In view of the above problems,a lightweight attribute-based encryption scheme using ordered binary decision diagram is proposed firstly which enriches the logical expression of the access policy and combines offline/online encryption and outsourced decryption.The scheme not only reduces the calculation burden but also avoids the correctness verification of ciphertext.On this basis,a lightweight attribute-based encryption scheme using blockchain is proposed in order to further reduce the calculation overhead.Blockchain is introduced to realize offline encryption and smart contracts are designed to solve the security problems caused by data disclosure on blockchain.The main work of this thesis includes:(1)A scheme named OBDD-LABE(lightweight attribute-based encryption using ordered binary decision diagram)is proposed,which divides the encryption phase into offline encryption phase and online encryption phase.The intermediate results obtained in offline encryption phase can be directly used in online encryption phase,which improves the encryption efficiency and avoids the verification of ciphertext due to the local encryption.The decryption phase is divided into outsourcd decryption phase and local decryption phase.Under the condition that the outsourced agent cannot know the plaintext,most of the calculation is transferred to the agent,so as to reduce the calculation burden of the decryptor.(2)A scheme named BC4OE-LABE(lightweight attribute-based encryption using blockchain for offline encryption)is proposed,and the blockchain is introduced to perform offline encryption,so that the the cryptographers can obtain the offline encryption result by invoking smart contract,further reducing the calculation burden of the cryptographers.In order to ensure that users on the blockchain cannot directly locate the trapdoor in the ciphertext module,the scheme of block confusion is designed.Based on the scheme,the version number and block identification are set,and the ciphertext module pool generation contract and ciphertext module acquisition contract are designed to ensure that users on the chain cannot maliciously extract trapdoor information from other users’ ciphertext modules,which ensures the high efficiency and security of the scheme.(3)Based on the aforementioned schemes,a lightweight attribute-based encryption system using blockchain is designed and implemented.The functional test and performance test of the prototype system show that the schemes proposed in this thesis not only reduce the calculation cost,but also ensure the availability and security of the system.