Abstract: There have been increasing demand and concerns for distributed security, with the recent adoption and diffusion of data sharing in distributed systems such as cloud computing.Enforcement of access policy and policy updates are the challenging issues in data sharing system.This issue can be solved by using cryptographic techniques.Cipher text policy attribute based encryption (CP-ABE) is one of the promising solution. It enables data owners to define their own access policies over user attributes and enforce the policies on the data to be distributed.The major drawback is the key escrow problem.Escrow means storage,here the key is stored in third party that is key generation centre. The key generation center could decrypt any messages addressed to specific users by generating their private keys. This is not suitable for data sharing scenarios where the data owner would like to make their private data only accessible to designated users. In addition, applying CP-ABE in the data sharing system introduces anotherchallenge with regard to the user revocation since the access policies are defined only over the attribute universe.The proposed scheme can solve the two problems key escrow problem and revocation problem.
Keywords: Removing Escrow, Revocation, Attribute Based Encryption, Access Control.