An Efficient Ciphertext-Policy Attribute-Based Encryption Scheme with Policy Update

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.

Distributed Certificateless Key Encapsulation Mechanism Secure Against the Adaptive Adversary

This paper proposes an adaptively secure solution to certificateless distributed key encapsulation mechanism from pairings by using Canetti＇s adaptive secure key generation scheme based on discrete logarithm. The proposed scheme can withstand adaptive attackers that can choose players for corruption at any time during the run of the protocol, and this kind of attack is powerful and realistic. In contrast, all previously presented threshold certificateless public key cryptosystems are proven secure against the more idealized static adversaries only. They choose and fix the subset of target players before running the protocol. We also prove security of this scheme in the random oracle model.

Generic Certificateless Encryption Secure Against Malicious-but-Passive KGC Attacks in the Standard Model

Despite the large number of certificateless encryption schemes proposed recently, many of them have been found insecure under a practical attack, called malicious-but-passive KGC （Key Generation Center） attack. In this work we propose the first generic construction of certificateless encryption, which can be proven secure against malicious-but- passive KGC attacks in the standard model. In order to encrypt a message of any length, we consider the KEM/DEM （key encapsulation mechanism/data encapsulation mechanism） framework in the certificateless setting, and propose a generic construction of certificateless key encapsulation mechanism （CL-KEM） secure against malicious-but-passive KGC attacks in the standard model. It is based on an identity-based KEM, a public key encryption and a message authentication code. The high efficiency of our construction is due to the efficient implementations of these underlying building blocks, and is comparable to Bentahar et al.＇s CL-KEMs, which have only been proven secure under the random oracle model with no consideration of the malicious-but-passive KGC attack. We also introduce the notion of certificateless tag-based KEM （CL-TKEM）, which is an extension of Abe et al.＇s work to the certificateless setting. We show that an efficient CL-TKEM can be constructed by modifying our CL-KEM scheme. We also show that with a CL-TKEM and a data encapsulation mechanism secure under our proposed security model, an efficient certificateless hybrid encryption can be constructed by applying Abe et al.＇s transformation in the certificateless setting.