Securing Cloud Data under Key Exposure

Abstract

The world recently witnessed a massive surveillance program aimed at breaking users privacy. Recent news reveal a powerful attacker which breaks data confidentiality by acquiring cryptographic keys, by means of coercion or back doors in cryptographic software. Once the encryption key is exposed, the only viable measure to preserve data confidentiality is to limit the attacker’s access to the ciphertext. ciphertext blocks across servers in multiple administrative domains thus assuming that the adversary cannot compromise all of them the world recently witnessed a massive surveillance program aimed at breaking users privacy. If the user upload the some file in the cloud while encrypting the data, but the hackers , whose know the key they hack that file very easily, so we provide a bastion algorithm, Bastion first encrypts the data with one round of block cipher encryption, and then applies an efficient linear post-processing to the ciphertext By doing so, Bastion relaxes the notion of all-or-nothing encryption at the benefit of increased performance ,so in this way we secure the owner files, if the file encrypted buy the owner, and then the owner give the authority to the user whose only download the file. In user side the all owner upload files are viewed, but if the user give the request to the authority file only ,otherwise if the one user did not have the authority to download the file, first the user give the request to the cloud service provider, the owner give the authority to the file is partially encrypted and send to the user, if the owner did not give the authority to the user , the file is not viewed, the data owner did not share this file to you message is displayed, but by mistake the cloud service provider accept the user request, that file send to that user but the user did not download the file.