International Journal of Computational Engineering Research(IJCER)

International Journal of Computational Engineering Research||Vol, 03||Issue, 6||
www.ijceronline.com ||June ||2013|| Page 9
A Presumable Data Retentive Framework for Multi Cloud
S.L Sailaja1
, S.Anjanayya 2
1M.Tech (CSE), SJCET- Kurnool (Dt), Affiliated to JNTUA University, Andhra Pradesh, INDIA.
2 Associate Professor, Department of CSE, SJCET- Kurnool (Dt), Affiliated to JNTUA University, Andhra
Pradesh, INDIA
I. INTRODUCTION
As high-speed networks and ubiquitous Internet access become available in recent years, cloud storage
has become a fastest profit growth point for many cloud storage service providers. As cloud computing
environment is completely built on open architectures and open interfaces, it provides high interoperability by
bringing multiple internal/external cloud services together. When coming to a distributed cloud environment,
say multi-cloud or hybrid cloud, it has to allow many clients to easily access their resources remotely through
web service interfaces. As the concept of cloud computing has become familiar, the need for opting of third
party storage servers also has its significant growth instead of setting up its own infrastructure for any
organization. Users just use services without being concerned about how computation is done and storage is
managed. Storage Outsourcing can also be referred to as data outsourcing or outsourcing of data.
Data outsourcing means the owner of the data (client) moves his/her data to a third-party storage
service provider(server) which is for a low fee, also faithful to the data owner. The significant features of data
outsourcing include reduced cost for storage, maintenance, increased availability and transparency of the data.
The main disadvantage of this kind of outsourcing is that the client /organization do not have any control over
the data which has been uploaded. The data as well as control of the data will be in the hands of the third party
which poses a question for maintaining the confidentiality of the data. Also the server does not guarantee
whether the data has been tampered with or deleted. Also, given a large files for storage, the user has to be
provided to validate the data without actually downloading the data. In this paper, we focus on designing a cloud
storage system for ensuring the integrity of the data in storage out sourcing. In this work, a cloud storage system
is considered as a large scale distributed storage system that consists of many independent storage servers.
II. EXISTING SYSTEM
To check for the integrity of outsourced data, researchers provides two basic approaches called
Provable Data Possession (PDP) and Proofs of Retrievability (POR). In the first approach, they proposed the
PDP model for ensuring possession of files on untrusted storages without downloading the actual data and
provided an RSA-based scheme for a static case. It also includes a challenge for public verifiability, with this
anyone, not just the owner can challenge the server for data possession.
ABSTRACT
Cloud Storage or storage outsourcing is a rising trend where the cloud storage service
provides a comparably low-cost, scalable, position-independent platform for storing client’s data. This
archival storage guarantees the authenticity of data on storage server, but does not guarantee for the
tampering of data (modifications or deletions, to the data).Thus, the problem for proving the integrity
of the data stored at the third party cloud service providers has increased its attention. This work
defines a framework for the efficient construction of data possession at the cloud storage servers
dynamically. This scheme is considered for a hybrid cloud in which multiple cloud storages servers are
considered, based on a cryptographic technique Interactive Proof System-multi-proved Zero
knowledge proof system. This system is based on homomorphic verifiable response from multiple cloud
servers, and the stored data is indexed using collision resistant hash index hierarchy. This scheme
satisfies the security properties of completeness, knowledge soundness, and zero-knowledge system.
This work also presents an optimal method for minimizing the computation, communication costs of
storage service providers.
KEYWORDS: Data possession, data outsourcing, storage outsourcing, probabilistic possession.

A Presumable Data Retentive Framework…
This extends the application areas of PDP protocol by separating the data owners and the users. But
this is insecure against replay attacks in dynamic scenarios because of dependencies in index of data blocks.
Moreover, they are not fit for multi-cloud storage because there is no homomorphic property in the verification
process. To overcome static file storage limits in PDP and to provide dynamic data operations in PDP the
Scalable PDP model have been proposed. It is a lightweight PDP scheme based on Cryptographic hash function
and symmetric key encryption. But due to the lack of randomness in the challenges the servers used to deceive
the clients /owners by previous metadata responses. Another drawback in this model is block size and its length
are fixed and hence the modification of blocks cannot be done anywhere. Based on this work two Dynamic PDP
has been proposed. First is the basic scheme, called DPDP-I and Second is the, “block less” scheme, called
DPDP-II. But these schemes are also not effective for a multi-cloud environment. Second approach is POR
scheme; it describes the preprocessing steps that the clients should do before sending their file to a CSP. But not
allow for updating the data efficiently. An improved version of this protocol called Compact POR has been
proposed. This technique which uses homomorphic property to aggregate a proof into authenticator value but
the solution is also static and could not prevent the leakage of data blocks in the verification process. The
dynamic scheme with cost by integrating the Compact POR scheme and Merkle Hash Tree (MHT) into the
DPDP has been proposed. Several POR schemes and models have been recently proposed by using RAID
techniques. It introduced a distributed cryptographic system that allows a set of servers to solve the PDP
problem. This is based on an integrity protected error correcting code (IP-ECC), which improves the security
and efficiency of existing tools. Here, a file must be transformed into distinct segments with the same length,
which are distributed across servers. It is more suitable for RAID rather than cloud storage.
2.1 Drawbacks of Existing System
1) The existing schemes apply to the case of static, archival storage. Also dependent on the number of file
blocks.
2) The numbers of updates, insertions, deletions are limited and are fixed
3) Insertions cannot be performed dynamically.
4) The existing schemes are vulnerable to two major security attacks: Data leakage attack and Tag Forgery
attack.
5) Mainly applicable for a single cloud storage environment, but not for a distributed cloud storage
environment.
III. PROPOSED SYSTEM
In this work, the architecture for a multi-cloud storage service can be viewed as three different entities:
Clients, Cloud Service Providers (CSP’s), Trusted Third party Administrator.
[1] Clients: End users who have large amounts of the data to be stored at third party storage servers. These
users have permissions to access as well as manipulate the data.
[2] CSP’s: CSP’s provide data storage services and possess enough computation and storage services.
[3] Trusted Third Party: The third party administrator who is trusted to store verification parameters, also
offer public query services for those parameters.
In this work, the verification procedure for data possession can be described as follows: Initially, the
client uses secret key to pre-process the file as a collection of n-blocks. For the processed n-blocks, verification
tags will be generated which are stored at the CSP’s along with the file. At the same time, he generates the
public verification information for the TTP’s. The client can delete his/her own local copy of the data. The TTP
acts independently and is reliable through the following functions:
[1] To setup and maintain the cryptosystem for the DPDP scheme.
[2] To generate and store owner’s public key
[3] To store the public verification parameters to execute the verification protocol of the DPDP scheme.
3.1 Provable Data Possession Schemes
In order to address the problem of data integrity and authenticity in a distributed cloud environment.
The following aspects are taken into consideration: High performance, scalability, automatic failure recovery,
verification transparency, high security. For an efficient construction of this scheme, a significant cryptographic
technique, Interactive Proof System with multi-prover Zero Knowledge Proof system is used for security
analysis. This model satisfies the security properties of completeness, soundness, zero-knowledge. The
verification framework for the distributed cloud environment is implemented using two techniques. They are
[1] Hash Index Hierarchy
[2] Homomorphic verifiable response.

This framework provides security by resisting data leakage attacks and Tag forgery attacks. The
framework can be defined as follows: Considering the security key and the tag for n-blocks of a file, the data
possession scheme is given as
S= (KeyGen, TagGen, Proof).
The above said is a collection of two algorithms
- (KeyGen, TagGen)
- Interactive proof system, say Proof, can be explained as follows:
𝐾𝑒𝑦(1 𝜅): a security parameter 𝜅 as input, and returns a secret key 𝑠𝑘 or a public-secret key pair (𝑝𝑘, 𝑠𝑘);
𝑇𝑎𝑔𝐺𝑒𝑛(𝑠𝑘, 𝐹,𝒫): This function takes as inputs a secret key 𝑠𝑘, a file 𝐹, and a set of cloud storage providerss 𝒫
={𝑃 𝑘}, and returns the triples (𝜁,𝜓, 𝜎), where 𝜁is the secret in tags, 𝜓 = (𝑢,ℋ) is a set of verification parameters
𝑢 and an index hierarchy ℋ for 𝐹, 𝜎 ={𝜎
( 𝑘)
}𝑃 𝑘∈𝒫denotes a set of all tags, 𝜎
( 𝑘)
is the tag of the fraction 𝐹
( 𝑘)
of
𝐹 in 𝑃 𝑘; 𝑃𝑟(𝒫, 𝑉): a protocol of proof of data possession between all CSPs (𝒫 = {𝑃 𝑘}) and a verifier (V), that
is, 〈Σ𝑃 𝑘∈(𝐹
( 𝑘)
, 𝜎
( 𝑘)
) ←→ 𝑉〉(𝑝𝑘, 𝜓)= {{1 𝐹 = {(F
( 𝑘)
)} is intact}, {0 𝐹 = {𝐹
( 𝑘)
} is changed}} ,where each 𝑃 𝑘
takes as input a file 𝐹
( 𝑘)
, a set of tags 𝜎
( 𝑘)
, a public key 𝑝𝑘, a set of public parameters 𝜓 as the common input
between 𝑃and 𝑉 . At the end of each run of the protocol, 𝑉 return as bit {0∣1} denoting false and true. Where,
Σ𝑃 𝑘∈𝒫denotes cooperative computing among all the CSP’s in 𝑃 𝑘∈𝒫. The co-operability among all the CSP’s
storing the same set of the data is verified one by one, i.e., ⋀𝑃 𝑘∈𝒫⟨𝑃 𝑘(𝐹
( 𝑘)
, 𝜎
( 𝑘)
) ←→ 𝑉⟩(𝑝𝑘, 𝜓), where ⋀
denotes the logical AND operations among the boolean outputs of all protocols ⟨𝑃 𝑘, 𝑉⟩on all the CSP’s for all
𝑃 𝑘∈𝒫.
IV . SYSTEM MODEL
4.1 Hash Index Hierarchy
The architecture for this data possession scheme is a hierarchial model of file storage. This structure
consists of three different levels which expresses the relationship among different storage resources:
1) Express Layer: an abstract representation of the stored resources.
2) Service Layer: manages and offers cloud storage.
3) Storage Layer: realizes data storage on many physical devices.
The storage layer defines a common fragment structure, a data structure that maintains a set of block-
tag pairs. Given a file of blocks (m1, m2,m3,…mn), the respective block-tag pair will be generated as (𝑚𝑖, 𝜎𝑖),
where 𝜎𝑖 is a signature tag of block 𝑚𝑖, generated by a set of secrets 𝜏 = (𝜏1, 𝜏2, ⋅⋅⋅ , 𝜏𝑠). To check for the data
integrity, the fragment structure implements the probabilistic verification as follows: Given a random
probabilistic query 𝑄 = {(𝑖 , 𝑣𝑖)}𝑖∈𝑅𝐼, where 𝐼 is a subset of the block indices and 𝑣𝑖 is a random Coefficient,
the constant-size response is derived as (𝜇1, 𝜇2, ⋅⋅⋅ , 𝜇𝑠, 𝜎′), where 𝜇𝑖 comes from all {𝑚𝑘,𝑖, 𝑣𝑘}𝑘∈𝐼 and 𝜎′ is
from all {𝜎𝑘, 𝑣𝑘}𝑘∈𝐼 To support virtualization of storage services, a simple Index-hash table 𝜒 = {𝜒𝑖} is
introduced to record the changes of file blocks as well as to generate the hash value of each block in the
verification process. The structure of index-hash table 𝜒 is similar to that of the structure of file block allocation
table in file systems. This index-hash table consists of parameter values of serial number, block number, version
number, and random integer. All the records in the index table are made unique to prevent forgery of data blocks
and tags. Using this index records {𝜒𝑖}, this scheme also support dynamic data operations.

4.2 Homomorphic Verifiable Response
A homomorphism is a map function f :ℙ → ℚ between two groups such that 𝑓(𝑔1 ⊕𝑔2) = 𝑓(𝑔1)
⊗𝑓(𝑔2) for all 𝑔1, 𝑔2 ∈ℙ, where ⊕ denotes the operation in ℙ and ⊗ denotes the operation in ℚ. This notation
has been used to define Homomorphic Verifiable Tags (HVTs). Given two values 𝜎𝑖 and 𝜎 𝑗 for two messages
𝑚𝑖 and 𝑚𝑗, anyone can combine them into a value 𝜎′ corresponding to the sum of the messages 𝑚𝑖 +𝑚𝑗. A
response is called homomorphic verifiable response in a Data Possession protocol, if given two responses 𝜃𝑖 and
𝜃𝑗 for two queries or challenges on 𝑄𝑖 and 𝑄𝑗 from two CSPs, then an efficient algorithm combines them into a
response 𝜃 corresponding to the sum of the challenges 𝑄𝑖∪. This Homomorphic verifiable response technique
not only reduces the communication bandwidth, but also conceals the location of outsourced data, i.e., from
which CSP the data is being accessed.
4.3 Working Model
This protocol can be described as follows: The manager who is a client first runs algorithm 𝐾𝑒𝑦𝐺𝑒𝑛 to
obtain the public/private key pairs for CSPs as well as public users. The clients generate the tags of outsourced
data by using 𝑇𝑎𝑔𝐺𝑒𝑛. The protocol 𝑃𝑟𝑜𝑜𝑓 is performed by a 5-move interactive proof protocol between a
verifier (client) and more than one CSP, in which CSPs need not to interact with each other during the
verification process, an organizer (TTP) is used to organize and manage all CSPs.
1) The organizer (CSP) initiates the protocol and sends a commitment to the verifier (Client).
2) The verifier returns a challenge set of random index-coefficient pair’s𝑄 to the organizer.
3) The TTP relays them into each 𝑃𝑖 in 𝒫 according to the exact position of each data block.
4) Each 𝑃𝑖 returns its response of challenge to the organizer.
5) The organizer synthesizes a final response from received responses from all the CSP’s and sends it to the
verifier.
In the above said process, this scheme would guarantee that the verifier accesses files without knowing
on which CSPs or in what geographical locations their files reside.
4.4 Advantages of Proposed System
1) Since these schemes are built based on collision-resistance signatures and random oracle model, these
schemes have short query and response from public verifiability.
2) In distributed cloud storage, a file is divide into sectors for which all the S sectors are represented
with a single tag, there by reducing the storage for all the tags for S sectors.
3) As this scheme rely upon homomorphic properties, for aggregation of data and tags, into a constant size
response, thereby minimizing the network communication bandwidth.
4) The hierarchial structure for storage provides virtualization for storage thereby concealing the location of
the storage servers.
V. SECURITY ANALYSIS
This scheme satisfies the security properties of Completeness, Soundness, and Zero-knowledge
1) Completeness – To challenge the data integrity and ownership, the secret information is required with the
verification protocol. The <Data, Tag> pair taken a (F,σ)ε TagGen(Sk,F), a random challenge is generated
given as Q – (I,Vi) where I ε I can be checked for the success probability.
2) Soundness - The verifier is infeasible to accept any responses. This property can be used as a stricter notion
for the unforgetability of the tags in order to avoid the ownership cheating. Hence, using this property, no
intruder or server can tamper the data or forge the data tags. This property can be used efficiently to resist
Tag Forgery attacks.
3) Zero –Knowledge – This property preserves the privacy of data blocks and respective tags to resist data
leakage attacks, by introducing a random integer λ j,k for a response the random integer is not
known to the intruders.
VI. CONCLUSION
In this paper, a cloud storage system that consists of multiple cloud servers is considered. This scheme
uses collision resistant hash index hierarchy model to store the data at multiple sites in an indexed manner. The
response from the multiple cloud servers is a homomorphic verifiable response from multiple cloud servers.
This work is completely based on multi-prover zero knowledge system, also satisfies all the security properties,
thereby minimizing the communication overheads and computational costs for storage providers.

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