Conditional proxy re-encryption for secure big data group sharing in cloud environment

Conditional PRE (CPRE) is a novel public key primitive which enables the group sharing of confidential data without revealing its plaintext or decryption key to outside the group member. Previously, several efforts are made to facilitate CPRE in group data sharing in cloud environment. The main drawback of the state-of-art CPRE schemes for this purpose is that whenever the group member changes, the originator of the data needs to download all of the existing data on the cloud, encrypt them again with a new condition value, and uploads them to the cloud. As a result, they are not suitable for secure big data sharing among group member in cloud environment. In this paper, we introduce a new CPRE called the outsourcing CPRE scheme (O-CPRE) which reduces the client overhead drastically. When the membership of the group changes, in O-CPRE, the originator only needs to select a new condition value and upload it to the cloud. In addition, O-CPRE will move a part of client overhead at the initial setup stage and at the decryption of each message from the client to the cloud. As a result, O-CPRE is much more suitable for secure big data sharing in cloud environment than the other existing schemes.