Development of Effective Audit Service to Maintain Integrity of Migrated Data in Cloud

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 03 Issue: 01 | Jan-2016 www.irjet.net p-ISSN: 2395-0072
© 2016, IRJET | Impact Factor value: 4.45 | ISO 9001:2008 Certified Journal | Page 722
Development of Effective Audit Service to Maintain Integrity of
Migrated Data in Cloud
Shekhar S. Kausalye1, Prof. P.N. Kalavadekar2
1 PG Student, Dept. of Computer Engineering, SRES COE, Kopargaon, Pune University, MH, INDIA
2 Associate Professor, Dept. of Computer Engineering, SRES COE, Kopargaon, Pune University, MH, INDIA
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Abstract - Cloud based service for storage of
outsource data reduces the burden of user for storage
management & maintenance, this is achieved because
cloud service provides low-cost, expandable &
geographically location independent platform. But
client has risk of missing or corrupted data as the local
copy is not available at client side. To avoid this security
risk audit service must ensure the integrity of data. PDP
technique which is used for verifying the integrity of
data can be used to understand the audit service. A PDP
protocol can be constructed using the interactive zero
knowledge system to prevent the fraud of prover as well
as leakage of verified data. This can be proved that the
protocol can persists these properties with the help of
Diffie-Hellman assumption. The mechanism can be
proposed to reduce cost of audit and to detect
misbehaviour with the help of related queries &
periodic verification.
Key Words: security, interactive proof system, cloud
storage, Audit Service, Provable Data Possession, etc…
1. INTRODUCTION
Cloud computing is growing service for current
information technology. IT provides scalable environment
for ever increasing amount of data & processes which
work on various application & services by using on-
demand self-services. The important advantage of cloud
computing paradigm is that data cam be outsourced and
centralized at different location called as clouds. This kind
of outsourced data storage service is becoming profitable
business because of flexible, low-cost, location-
independent platform to manage user data.
The burden of storage management & maintenance is
reduced by Cloud Storage Service (CSS). But if this
important service is susceptible to failure of attacks then
this will be causing the irretrievable loss of user data as
this data is not available locally with user. This risk can be
caused due to: cloud infrastructure is vulnerable to
security threats from within and outside of cloud [2]; the
Cloud Service Providers (CSP) can behave untruthfully for
cloud users [3]; also, the different opinion may be there
because of faithfulness of CSP. Accordingly, their
behaviour is unknown for different clients even though
this may result from user’s incorrect actions [4]. Because
of all these reasons its cloud service provider
responsibility to issue an efficient audit service so that the
integrity and data availability can be verified on cloud data
[5].
There are various traditional cryptographic technologies
are available for data integrity and availability which are
based on hash function and signature schemes [6][7]. But
these technology does not work on outsourced data as
they must have the local copy of data to perform the audit.
As well as this process is not feasible to perform the
validation by downloading data because of expensive
transaction if file size is large. Also to perform the audit in
cloud environment is difficult and costly for the users [8].
Therefore, it is important to understand the public
auditability for CSS, because of which users may use or
take help of Third Party Auditor (TPA). This TPA is expert
and has capabilities that user don’t have to perform the
audit on outsourced data.
For this auditability the concept of Proof of Retrievability
[9] commonly called as POR and Provable Data Possession
[10] (POP) is given by researchers. Probabilistic proof
techniques approach is used by them to show that user’s
data remain intact without downloading it, and this is
called as “Verification without Downloading.” Anyone can
use the verification protocol to prove the availability of
data using PDP or POR scheme. Hence this fulfils the
requirement of public auditability. These schemes are
developed around and untrusted storage which offer to
check the very large amount of data.
Various existing scheme does not give the security proof
against Cloud Service Provider’s fraud and counterfeits as
well as information leakage. These problems reduce the
impact of cloud audit service. Because of this new model of
framework must be proposed that enables the security of
public verification protocol in audit service.
The performance of audit service is depending on the
three aspects which are:
• How to design an efficient architecture of audit
system that reduce the storage and network
overheads and also enhance the security of audit
activities;

• How to provide an efficient audit scheduling to
help provide a more cost-effective audit service;
• How to optimize parameters of audit systems to
minimize the computation overheads of audit
services.
Quality of service can be improved by solving above
problems and it also help to detect irregularities and
requires less resources.
2. EASE OF USE
Various researchers worked on the untrusted outsourced
data. The simplest and easy way to implement the
integrity control is to use cryptographic hash function.
Yumerefendi [7] and Hsiao[6] proposed a solution for
authenticated network storage, Merkle tree also called as
hash tree as the fundamental data structure, but their
update process is costly. Fu [11] implemented & described
the method for securely accessing a read only file system
which is distributed among the various providers. This is
the solution for efficiently authenticating operation on
outsourced data or file.
The work done by Li[12], Ma[13], Xie[14], Yavuz[5]
considered the problem of how to audit the integrity of
outsourced data or database. From these Li & Xie used the
concept of Markle tree to audit the completeness of query
result, but in some cases the overhead is high that weaken
the benefits of database outsourcing. Some researchers
proposed two schemes called PDP & POR to check the
integrity of stored data without downloading it. Ateniese
proposed the Provable Data Possession model to ensure
the possession of file on untrusted storage and also
provides the RSA based scheme that achieves O(1)
communication cost. Anyone other than owner can
challenge the server for data possession using the publicly
verifiable version.
The dynamic PDP solution called scalable PDP [15] is
developed by the Ateniese. This is achieved using the
Lightweight PDP scheme which used cryptographic Hash
function & symmetric key encryption, but server can
victimize the user as lack of randomness in the challenge
in previous response. The number of updates and
challenges is fixed and limited. By studying this work
Erway has proposed two dynamic PDP [16] scheme using
Hash function tree to cognize O(log n) communication and
computation cost of data (file) which contain n blocks. The
drawback of SPDP is simple scheme called DPDP-I and in
the “block-less scheme’ which is generally called as DPDP-
II the data block can be leaked by response given to
challenge.
But Juels presented the POR [9] scheme which greatly
cognize of pre-processing steps of the client which are
followed before sending the file or data to Cloud Service
Provider. The main drawback of this scheme is that these
operation restricts the updating of data. Shacham &
Waters [17] presented and efficient version of this
protocol which is called Compact POR, this protocol uses
harmonic property to aggregate a proof into O(1)
authenticator value and O(t) computation cost where t is
challenge blocks, but the drawback of this is that its
solution is static and there is leakage of data blocks in the
verification process.
3. LITERATURE SURVEY
Audit system architecture for outsourced data in cloud is
shown in Fig. 1. This architecture work in audit service
outsourcing mode. This architecture contains four entities:
1. Data Owner (DO): The user who want to store
large amount of data to the cloud;
2. Cloud Service Provider (CSP): CSP provides data
storage service and has storage space and
computation resources;
3. Third Party Auditor (TAP): TPA has capabilities to
manage of monitor outsources data under the
deputation of data owner;
Granted Application (GA): GA has rights to access &
manipulate stored data. These application can be either
inside the cloud or outside the cloud. This depends on the
specific requirement.
Fig-1. Audit System Architecture for Cloud Computing
Audit service based on TPA works in the following way.
This also help to describe our audit service as follows:
1. Client uses the secret key sk for preprocessing of
the file, file contains collection of n blocks, then it
generates public verification information which is
stored in TPA, after this the file is transmitted
with some verification tags to Cloud Service
Provider, user can then delete the local copy of
this data;
2. Afterword, using protocol called as proof of
retrievability, TPA check the integrity and
availability of the outsourced data. It is important
to generate an alarm for suspicious activity or
events. [1].
This is also known as audit service outsourcing because
verification of data integrity can be implemented by TPA
without taking help of data owner. Here data owner and
granted clients dynamically interact with Cloud Service
Provider to access or update their own data for various

application purposes. However, we cannot trust CSP for
security of stored data, neither can we assume that data
owner is able to collect the evidences against CSP for CSPs
fault when errors occur. Because of these reasons, TPA,
which act as a Trust Third Party (TTP), is used to make
sure the security of stored data. We can say that the TPA is
reliable as well as independent, and hence it has no
motivation to conspire with the CSP or clients at the time
of auditing process:
1. TPA must regularly check the integrity and
availability of data at appropriate intervals;
2. TPA must be able to take evidences for various
disagreements about inconsistency of the data in
terms of authentic records for all the data
operations.
4. IMPLEMENTATION
In this proposed audit architecture, main idea is, to
maintain security of Third Party Auditor so that we can
guarantee the credibility of cloud storage. Because it is
easy to ensure the security of Trust Third Party Auditor
than maintaining the security of whole cloud. Hence, Third
Party Auditor is the root or basis of trust in clouds. The
protocol design must achieve following security and
performance guarantees:
 Audit without downloading: Allow Third Party
Auditor or clients with the help of Third Party
Auditor to verify correctness of data whenever
necessary without downloading the copy of data;
 Verification correctness: to ensure there is no
cheating of CSP that can clear or grant the audit
from Third Party Auditor without storing user’s
data intact;
 Privacy-preserving: to ensure that there is no
alternate way for Third Party Auditor to derive
user’s data from information collected during the
audit operation; and
 High-performance: to allow Third Party Auditor
to perform auditing but with minimum overheads
for storage, communication and computation [1]
In this proposed audit architecture, main idea is, to
maintain security.
4.1 Design
A cryptographic interactive audit scheme is used to
support the audit service. This scheme is also called as
interactive PDP (IPDP). A standard model of interactive
proof system is used to construct this scheme, because this
ensures the confidentiality of secret data also called as
zero-knowledge property & the undeceivability of invalid
tags called as soundness property.
Definition Collision Resistance Hash: A hash family H is (t,
ε) collision resistance if no t-time advantage at least ε in
breaking the collision resistance of H [1]. The system is
setup using bilinear pairing proposed by Boneh & Franklin
[18]. Let be two multiplicative groups using elliptic
curve convention with large prime order p. A function e
can be bilinear map which can be computed as: e:
.
This has following properties: for any G, H ε & all a, b ε
, we have the following –
1. Bilinearity: e([a]G; [b]H) = e(G; H) ab1:
2. Non-degeneracy: e(G; H) 6 = 1 unless G or H
= 1.
3. Computability: e(G; H) is efficiently
computable [1]
Definition Bilinear map group system: It is a tuple
composed as the object as described above
[1].
4.2 Algorithm
Interactive audit protocol is based on the interactive proof
system as explained below: A cryptographic interactive
audit scheme S is consisting of two algorithms & one proof
system generally called as interactive proof system, i.e. S =
(K, T, P).
Algorithm 1: KeyGen (1s)
Security parameter s is given as an input to this algorithm,
and the algorithm return a public keypair (pk,sk) as:
Step 1: Let be a bilinear map group
system with randomly selected generators g, h, ∈R, ,
where , T are two group of large prime order p, |p|=
O(k).
Step 2: Now we generate the collision-resistance hash
function Hk(•) and by choosing a random α, β, ∈R,, p and
compute H1 = hα and H2 = hβ ∈ .
Step 3: Thus the secret key is sk = (α, β) and the public key
is pk = (g,h,H1,H2).
Algorithm 2: TagGen (sk,F)
This algorithm takes an secret key and a file F as input.
This returns a triplet ,
where denotes the secret used to generate verification
tag, is the set of public verification parameters u and
index information i.e., denotes the set of
verification tags;
1. Owners file i.e. F is splited in to n x s sectors
F={mi,j} ∈ ,
2. Choose s and random as the secret
of the file.
3. Compute for i ∈ [1, s] and
, where and Fn is the file
name.
4. Build index table .
5. Calculate its tag as:
where and i ∈ [1,n].
Sends and outputs ,
to TPA, and to CSP.

Proof (CSP,TPA): It is two-party proof protocol of
retrievability between CSP (prover) and TPA (verifier)
where CSP takes File as input, set of tags, a public key pk,
and a set of public parameter are the common input
between CSP and TP. At the end TPA return 1 or 0, where
1 shows the file is correct stored on the server. This
protocol is the three move protocol between Cloud Service
Provider and Third Party Auditor. Here the common input
is (pk, ψ). This protocol is:
 Commitment (CSP → TPA)
CSP choose random
for j ∈ [1,s], and sends its commitment to TPA,
where and
 Challenge (CSP ← TPA)
TPA choose a random challenge set I of t indexes along
with t random coefficients . Let Q be the set
of challenge index coefficient pairs. TPA sends Q
to CSP.
 Response (CSP → TPA)
CSP calculates the response Θ, μ as
Where, . P sends to V.
 Verification:
TPA can check that the response was correctly
formed by checking that
The proposed audit scheme is explained above, which
contains three algorithms namely key generation, tag
generation and verification protocol. In key generation
used is assigned a secret key sk this key is used to
generate tags for files and public key pk is used to verify
the integrity of stored files. In tag generation file F
produces the verification parameter . The hash
value can be considered as a signature of secret
and is the encryption of this secret.
Hash index table is designed according to the
Fig. -2
Framework of
interactive
audit scheme
application.
The index
table is
important for ensuring the security of the file. Using and
the hash value is generated for each block of file.
But it must be checked that values of should be
different for all processed files.
The verification process consists of three move
protocol structure which contains three steps i.e.
commitment, challenge and response. This is shown in
Figure 2.
This protocol is similar to Schnorrs ∑ protocol. The zero
knowledge property ensures that the verification process
does not expose anything other than veracity of the
statement in cloud. To avoid the leakage of data and tags
in the verification process, the secret data {m,j} is
protected by random .And the values and
are protected by simple commitment process.
4.3 Mathematical Model
It is P Class problem because: 1. Problem can be
solved in polynomial time. 2. All important operations are
hidden by KeyGen and TagGen algorithm. 3. The proof
protocol works in polynomial time. Let S be the set of
input function and output. So S = I, F, O where I is a set of
Input F is a set of functions that are used to process the
input provided and O be the set of output. I = I1, I2, I3 F =
F1, F2, F3 O = O1, O2, O3 Input is mapped to output which
is shown in following Venn diagram:
Fig-3. Venn diagram
As we have three input for the system, so we have three I
as
I1: File uploaded by user.
I2: Security parameter s which is bilinear map
group system.
I3: Secret key
I4: set of tags
Three functions are used F1, F2, and F3

F1: Key generation to generate the secret key.
F2: Tag Generation for file uploaded by user.
F3: Proof Technique to verify the files and
perform the audit.
Also the system has three outputs O1, O2, O3
O1: File Verification
O2: File is available for download (Retrieve File
after making changes by user)
O3: Perform periodic audit
5. RESULT
The implementation of system consists of implementation
of KeyGen algorithm. The input given is user id and
password. The bi-linear map group system is used with
two groups of large prime order. The key is generated
using the collision resistant hash function. While logging
to the system user has to enter the key which is sent to the
registered e-mail id of the user. This key is e-mailed to the
user when he attempt to log in using the user id and
password. The tag is generated using TagGen algorithm
which accepts two inputs secret key sk and file. The file is
uploaded with this tag to ensure the integrity while we are
performing the audit.Audit system architecture for
outsourced data in cloud.
6. CONCLUSIONS
Cloud-based outsourced storage reduces the client’s
burden for storage management and maintenance by
providing a low cost, scalable, location-independent
platform. But, the clients may not have local copy of this
data. To avoid the security risks, audit services must
ensure the integrity and availability of outsourced data.
This dissertation presents a construction of an efficient
audit service for data integrity in clouds. It also proposed
an interactive audit protocol to implement the audit
service based on a third party auditor.
In this audit service, the third party auditor, can issue a
periodic verification to monitor the change of outsourced
data by providing an optimized schedule. To realize the
audit model, there is only need to maintain the security of
the TPA. This technology can be easily adopted in a cloud
computing environment to replace the traditional Hash-
based solution.
ACKNOWLEDGEMENT
It is with the greatest pleasure and pride that I present this
paper. At this moment, I cannot neglect all those who
helped me in the successful completion of this paper. I am
very thankful to my respected project guide Prof. P. N.
Kalavadekar, Associate Professor, for his ideas and help
proved to be valuable and helpful during the creation of
this paper and guide me in the right path. I would also like
to thank all the faculties who have cleared all the major
concepts that were involved in the understanding of
techniques behind this paper. Lastly, I am thankful to my
friends who shared their knowledge in this field with me
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