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PANDA: PUBLIC AUDITING FOR SHARED

DATA WITHEFFICIENT USER REVOCATION IN

THE CLOUD

ABSTRACT

In the cloud environment users can easily modify and share data as a group. To ensure shared data integrity can be verified publicly, users in the group need to compute signatures on all the blocks in shared data. Different blocks in Shared data are generally signed by different users due to data modifications performed by different users. For security reasons, once a user is revoked from the group, the blocks which were previously signed by this revoked user must be re-signed by an existing user. The straight forward method, which allows an existing user to download the corresponding part of shared data and re-sign it during user revocation, is inefficient due to the large size of shared data in the cloud. In this paper, we propose a novel public auditing mechanism for the integrity of shared data with efficient user revocation in mind. By utilizing the idea of proxy re-signatures, we allow the cloud tore-sign blocks on behalf of existing users during user revocation, so that existing users do not need to download and re-sign blocks by themselves. In addition, a public verifier is always able to audit the integrity of shared data without retrieving the entire data from the cloud, even if some part of shared data has been re-signed by the cloud. Moreover, our mechanism is able to support batch auditing by verifying multiple auditing tasks simultaneously. Experimental results show that our mechanism can significantly improve the efficiency of user revocation.

EXISTING SYSTEM	PROPOSED SYSTEM
EXISTING CONCEPT:- In existing we have to download entire resigning blocks data from the cloud. This takes much time and bandwidth. For the integrity reasons we have to verify entire resigning data downloaded from the cloud with the resigning keys. The straight forward method, which allows an existing user to download the corresponding part of shared data and re-sign it during user revocation, is inefficient due to the large size of shared data in the cloud.	PROPOSED CONCEPT:- The original user acts as the group manager, who is able to revoke users from the group when it is necessary. It is necessary for the cloud service providers to storage data and keys separately on different servers inside the cloud in practice. We assume the cloud has a server to store shared data, and has another server to manage resigning keys.  The main focus of this paper is to audit the integrity of cloud shared data without downloading entire data from the cloud.
EXISTING TECHNIQUE:- Cipher text-policy attribute-based encryption techniques.	PROPOSED TECHNIQUE:- Panda
TECHNIQUE DEFINITION:- It is a type of public-key encryption in which the secret key of a user and the cipher text are dependent upon attributes. For proof access data if at least one individual key grants access.	TECHNIQUE DEFINITION:- Panda is public auditing Mechanism.It has following algorithms. KeyGen, Re-KeyGen, SignGen, Re-SignGen, ProofGen  and ProofVer.
DRAWBACKS:- Maintenance Cost is high for checking all the resigning keys in the cloud. Security and Integrity is low. Require more bandwidth to download.	ADVANTAGES:- Maintenance cost is low. Security is high for using the resigning keys. Downloading speed is high.