A decentralized multi-authority ciphertext-policy attribute-based encryption with mediated obfuscation

Abstract

To ensure security and obtain fine-grained data access control policies in many management domains, multi-authority attribute-based encryption (MA-ABE) schemes were presented and have been applied in cloud storage system. There exist certain scenes where the application domains managed by different attribute authorities ($$ AAs $$) often change, and hence domain managements require more autonomous and independent. However, most of existing schemes do not support flexible managements. In order to support dynamic managements, we propose a new decentralized ciphertext-policy MA-ABE scheme with mediated obfuscation (MA-DCP-ABE-WMO) where each of $$ AAs $$ works independently without any interaction with other $$ AAs $$. When issuing a secret key to a user, each of $$ AAs $$ uses his secret to compute a share of the system master secret. Data are encrypted under the public keys of attribute management domains. To resist collusion attack, a common pseudorandom function $$ PRF( \cdot ) $$ is shared among $$ AAs $$ and is used to randomize each user’s global identifier $$ Gid $$. The randomized $$ Gid $$ is adopted to unify all target messages which need to be reconstructed from different management domains. We first introduce the mediated obfuscation (MO) model into MA-ABE scheme to provide online service and the interaction works among data owner, data user and the mediator. In the MO model, we define a special functional encryption scheme where the function program can be coded into an element of the multiplicative cyclic group. We obfuscate the function by randomly selecting a blinding factor to conduct exponent arithmetic with the base of the function. A special input of the function is constructed to cancel the blinding factor when calling the obfuscated function. It makes other participants know nothing about the inner function program but can evaluate the function program. Furthermore, the MA-DCP-ABE-WMO scheme is proved to be secure. Compared with related schemes, our scheme is suitable to dynamic domain managements. When the management domains are added or removed, the workload to update original ciphertexts and private keys is dramatically reduced.