Assume the above diagram there is one file F stored in cloud is divided onto n blocks

m (i=1,2,3,4….). The lifetime of file F in our system mode not be fixed at first. by that means

The total number of time periods in unbounded, which is close to reality. The TPA cannot forget the authenticator for any block through his secrete key and generates update message.

The TPA might update incorrectly key generation algorithm. There are chances that TPA might provide wrong key to client from some reason. We say a strong key-exposure resilient auditing for secure cloud storage is verifiable if the TPA provides the wrong update key. He cannot pass the verification of our proposed scheme.

B. De?nition and Security Model:

De?nition 1:

A strong key-exposure resilient auditing scheme for privacy cloud storage contains six

Algorithms as follows:

1. System setup algorithm SysSetup:

This was run by the clients. Takes input as a security parameter k, and updates a system public key pk , The TPA’s secrete key SKTPA and the client’s private key SKc.

2. Update message generation algorithm UMGen:

At starting the algorithm run by client side of each interval of time. The input taken as public key PK, the current period t and the TPA’s secret key SKTPA, and generates an update message ?t

3. Client key update algorithm CKeyUpdate:

This algorithm is run by the client at the beginning of each period. It takes as input the public key PK, the current period t, the update message ?t and the client’s private key SKc, and generates the signing secret key SKt for time period t.

4. Authenticator generation algorithm AuthGen:

This algorithm is run by the client. It takes as input the public key PK, the current time period t, the client’s signing secret key SKt and a ?le F, and generates a set of authenticators ? for F in time period t.

5. Proof generation algorithm ProofGen:

This type of algorithm run by cloud side. The input taken as public key pk, at time lapse, a challenge Chal, a ?le F and a set of authenticators ?, and generates a proof P that is used to prove the cloud stores F correctly. In this algorithm, the (t,Chal) pair is issued by the TPA, and then used by the cloud as input.

6. Proof verifying algorithm ProofVerify:

This algorithm executed by TPA, it takes input as public key PK, in a time interval t, a challenge Chal an proof P ,and returns “true” if the veri?cation passed; or “false”, otherwise