Ciphertext-policy attribute-based encryption(CP-ABE)is a promising cryptographic solution to the problem for enforcing fine-grained access control over encrypted data in the cloud.However,when applying CP-ABE to data ...Ciphertext-policy attribute-based encryption(CP-ABE)is a promising cryptographic solution to the problem for enforcing fine-grained access control over encrypted data in the cloud.However,when applying CP-ABE to data outsourcing scenarios,we have to address the challenging issue of policy updates because access control elements,such as users,attributes,and access rules may change frequently.In this paper,we propose a notion of access policy updatable ciphertext-policy attribute-based encryption(APU-CP-ABE)by combining the idea of ciphertext-policy attribute-based key encapsulation and symmetric proxy re-encryption.When an access policy update occurs,data owner is no longer required to download any data for re-encryption from the cloud,all he needs to do is generate a re-encryption key and produce a new encapsulated symmetric key,and then upload them to the cloud.The cloud server executes re-encryption without decryption.Because the re-encrypted ciphertext is encrypted under a completely new key,users cannot decrypt data even if they keep the old symmetric keys or parts of the previous ciphertext.We present an APU-CP-ABE construction based on Syalim et al.’s[Syalim,Nishide and Sakurai(2017)]improved symmetric proxy re-encryption scheme and Agrawal et al.’s[Agrawal and Chase(2017)]attribute-based message encryption scheme.It requires only 6 bilinear pairing operations for decryption,regardless of the number of attributes involved.This makes our construction particularly attractive when decryption is time-critical.展开更多
Based on experimental data,this paper confirms,in a controlled environment,converging theoretical and empirical results that,when individuals insure,they choose to insure themselves with a full cover.This insurance be...Based on experimental data,this paper confirms,in a controlled environment,converging theoretical and empirical results that,when individuals insure,they choose to insure themselves with a full cover.This insurance behaviour creates an opportunity for the public authority to drive people to enter the insurance market where they would buy full insurance.This paper also sheds light on the risks of an opportunistic insurers’behaviour.This heuristic challenges the efficiency of separating contracts designed to address adverse selection issues.Indeed,a strong preference for full contracts may encourage low-risk individuals to turn to(full)contracts designed for high-risk individuals,yielding advantageous selection opportunities for insurers.However,if this heuristic strengthens the high-risks’reluctance for partial insurance,it may increase the efficiency of the separating contracts,and the lowrisk individuals suffer less from adverse selection.展开更多
基金This research is funded by Science and Technology Program of Guangzhou(Grant No.201707010358).
文摘Ciphertext-policy attribute-based encryption(CP-ABE)is a promising cryptographic solution to the problem for enforcing fine-grained access control over encrypted data in the cloud.However,when applying CP-ABE to data outsourcing scenarios,we have to address the challenging issue of policy updates because access control elements,such as users,attributes,and access rules may change frequently.In this paper,we propose a notion of access policy updatable ciphertext-policy attribute-based encryption(APU-CP-ABE)by combining the idea of ciphertext-policy attribute-based key encapsulation and symmetric proxy re-encryption.When an access policy update occurs,data owner is no longer required to download any data for re-encryption from the cloud,all he needs to do is generate a re-encryption key and produce a new encapsulated symmetric key,and then upload them to the cloud.The cloud server executes re-encryption without decryption.Because the re-encrypted ciphertext is encrypted under a completely new key,users cannot decrypt data even if they keep the old symmetric keys or parts of the previous ciphertext.We present an APU-CP-ABE construction based on Syalim et al.’s[Syalim,Nishide and Sakurai(2017)]improved symmetric proxy re-encryption scheme and Agrawal et al.’s[Agrawal and Chase(2017)]attribute-based message encryption scheme.It requires only 6 bilinear pairing operations for decryption,regardless of the number of attributes involved.This makes our construction particularly attractive when decryption is time-critical.
基金This work is partially supported by a grant overseen by the French National Research Agency(ANR)in the Investissement d’Avenir programme,through the iCODE Institute project funded by the IDEX Paris-Saclay[Grant No.ANR-11-IDEX-0003-02]。
文摘Based on experimental data,this paper confirms,in a controlled environment,converging theoretical and empirical results that,when individuals insure,they choose to insure themselves with a full cover.This insurance behaviour creates an opportunity for the public authority to drive people to enter the insurance market where they would buy full insurance.This paper also sheds light on the risks of an opportunistic insurers’behaviour.This heuristic challenges the efficiency of separating contracts designed to address adverse selection issues.Indeed,a strong preference for full contracts may encourage low-risk individuals to turn to(full)contracts designed for high-risk individuals,yielding advantageous selection opportunities for insurers.However,if this heuristic strengthens the high-risks’reluctance for partial insurance,it may increase the efficiency of the separating contracts,and the lowrisk individuals suffer less from adverse selection.
