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                    <p class="art-type" id="articleinfo">Research Article</p>
		    <p class="art-title">Privacy Preserving Keyword Search for Multiple Data Users in Cloud</p>
		    <p class="art-author"><?php $authors="Naresh Ramu<sup>1*</sup>, N Deepa<sup>2</sup> and P Pandiaraja<sup>2</sup>"; echo (stristr($authors,$coauthor))?str_replace($coauthor,"<a href='".$extpath."authors/".$courl."' target='_blank'>".$coauthor."</a>",$authors):$authors; ?></p>
<p class="art-affl"><sup>1</sup>Associate Professor, SRM Institute of Science and Technology, Kattankulathur, Tamil Nadu, India<br/>
<sup>2</sup>M. Kumarasamy College of Engineering, Karur, Tamil Nadu, India</p>
		    <p class="art-aff"><b>*Corresponding author: <?php $corresponding_author="Naresh Ramu"; echo ($coauthor!="" && $coauthor==$corresponding_author)?"<a href='".$extpath."authors/".$courl."' target='_blank'>".$coauthor."</a>":$corresponding_author;?></b>,
Associate Professor,
SRM Institute of Science and Technology,
Kattankulathur, Tamilnadu,
India,
Tel: 91-80566 62701,
E-mail: <a href="mailto:naresh.r@ktr.srmuniv.ac.in">naresh.r@ktr.srmuniv.ac.in</a></p>
<p class="art-aff"><b>Received:</b>   November 23, 2018
<b>Accepted:</b>    November 30, 2018
<b>Published:</b> December 5, 2018</p>
<p class="art-aff"><b>Citation:</b> 
Naresh R, Deepa N, Pandiaraja P. Privacy Preserving Keyword Search for Multiple Data Users in Cloud. <i>Madridge J Bioinform Syst Biol</i>. 2018; 1(1): 1-4. doi: <a href="https://doi.org/10.18689/mjbsb-1000101">10.18689/mjbsb-1000101</a></p>
<p class="art-aff"><b>Copyright:</b> &copy; 2018 The Author(s). This work
is licensed under a Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium, provided the
original work is properly cited.</p>
<p><a href="<?php echo $extpath;?><?php echo $jres['journal_link'];?>/mjbsb-1000101.pdf" class="btn btn-danger pull-right" target="_blank">Download PDF</a></p>
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<div class="articlecontent">
<p class="art-subhead" id="abstract">Abstract</p>
<p class="art-para">By the start of cloud computing as well as its benefits the data owners submits their
files to cloud service providers which allow the data users to download the searched
files. For maintaining the privacy of the files andto have secure search over encrypted
files. We have developed the privacy preserving keyword search for multiple data user's
incloud. There are many existing papers which supports the same privacy as well as the
secure search by using the single owner model. But, utmost cloud servers in real time do
not just support one data owner, as a substitute, the cloud server will maintain multiple
data owners to enjoy the advantages provided by the cloud. In this research paper, we
propose a protocol which will support the short and secure trapdoor to have the secure
search over the cloud. By using our protocol even the cloud service providers will not
able to find the corresponding search request as well as the data user trapdoor. We
have developed the secure trapdoor phase to have the secure search over the cloud. We
have developed the cloud matching phase to have the ranked results. We also have
developed the decryption phase to decrypt the encrypted files. The performance
evaluation and the security evaluation are presented to prove that our protocol is better
in terms of computation complexity as well as the communication complexity.</p>

<p class="art-para"><b>Keywords:</b> Cloud computing; Privacy; Multi data owner; Keywords; Trapdoors; Communication complexity; Computation complexity.</p>

<p class="art-subhead" id="intro">Introduction</p>
<p class="art-para">Cloud computing is a surprising technology that is varying as a mode that the
hardware in addition to software are constructed and acquired <a href="#1" id="ref1">[1]</a>. As an innovative
prototype of computing, the cloud computing delivers plentiful advantages like easy
way of accessing reduced costs, fast deployment in addition to flexible maintenance of
resources. All size of companies can outsource the documents to the cloud to raise
invention also partnership.</p>

<p class="art-para">Cloud service providers will give assurance to the data owners by using the files
security methods like virtualization as well as firewalls. Though, these methods do not
support data owners' privacy, since the cloud itself holds full control over the data
owners' files. By encrypting the files before outsourcing can save the data privacy beside
cloud. Still, file encryption creates a challenging issue for utilizing the data from the
cloud.</p>

<p class="art-para">Song et al. <a href="#2" id="ref2">[2]</a> first define and resolve the difficulty of secure search over encrypted
files. They recommend the idea of searchable encryption. Search on an encrypted
dataset just as on a plaintext dataset. Searchable encryption is additionally developed
by Goh E et al. <a href="#3" id="ref3">[3</a>-<a href="#7" id="ref7">7]</a>.</p>

<p class="art-para">However, these schemes care mostly on single or Boolean
keyword search. Extending these methods for ranked multikeyword search will suffer from heavy computation complexity
and storage complexity. Secure search over encrypted files
placed over the cloud is first initiated by Wang et al. <a href="#8" id="ref8">[8]</a> and
additionally established by Cao N et al <a href="#9" id="ref9">[9</a>-<a href="#14" id="ref14">14]</a>. Extending the
single data owner system to the multi data owner scheme will
create more difficulties. In the single data owner system, when
the data user requires submitting a keyword search, the data
users ask the secret keys from the data owner for generating
the trapdoors. If there are numerous data owners then asking
the keys from all the data owners will be difficult for the data
users.</p>

<p class="art-para">Initially, it is not necessary for all the data owners to stay in
online continuously to deliver the keys whenever the data user
submits the query. Moreover if the data owners were in offline
means they cannot deliver the keys to the data user when the
search request is submitted. Another issue is whenever the
data user has to submit the search request towards the
encrypted files placed over the cloud by various data owners,
definitely the data users has to submit generate the different
trapdoors. If the data user submits more trapdoor to the
various data owner individually means it would create more
communication as well as computation complexity. Another
resolution is to share a secret key among whole data owners.
When the data user trapdoor and the data owner encrypted
keyword matched then the cloud will do the matching process
to return the best related search results to data users without
leaking any secret information from the files.</p>

<p class="art-para"><b>The main contributions of this paper are listed as follows:</b></p>
<ul>
<li>The secure keyword generation for encrypting as well
as for decrypting the files.</li>
<li>We define a trapdoor for secure keyword search over
encrypted cloud data, which is used for preserving
the privacy. This trapdoor not only permits the cloud
server to perform secure ranked keyword search
without knowing the actual data of both search
request as well as trapdoors, but also permits data
owners to encrypt keywords through their own keys.
Finally the authenticated data users can submit the
search request without aware about the data owner
keys. We implement the experiments on existing
world datasets to prove the efficiency of our proposed
schemes.</li>
<li>The cloud matching phase to match the trapdoor and
the data owner index.</li>
</ul>
<p class="art-para">The rest of this paper is organized as follows. Section 2
explains the related works. Section 3 describes the notations
and our proposed protocol. Section 4 presents security
analysis. Section 5 explains the performance analysis. Section
6 describes the conclusions and the future works.</p>

<p class="art-para"><b>Related Work</b><br/>
In this related work section, we describe three types of
work: searchable encryption, secure keyword search in cloud,
and cloud matching the encrypted files. Initially the Searchable Encryption is the first effort of searchable encryption was
done by Song et al. <a href="#2" id="ref2">[2]</a>
</p>

<p class="art-para">D. Song et al. <a href="#2" id="ref2">[2]</a> have proposed a method to encrypt
every word in a file individually and permit the server to find
whether that particular single keyword is present in the file
without aware of that exact word. This method suffers from
high computational complexity. Goh et al. propose to
construct a keyword index for each file using Bloom filter to
have a quick search <a href="#3" id="ref3">[3]</a>. Curtmola et al. propose to build
indices for each keyword using hash tables as amethod for
searchable encryption <a href="#4" id="ref4">[4]</a>. P. Golle and L. Ballard <a href="#6" id="ref6">[6</a>,<a href="#7" id="ref7">7]</a>
additionally improve the search functionalities of searchable
encryption by using conjunctive keyword search. The
searchable encryption suits for the single keyword search or
boolean keyword search. Extending these methods for multikeyword search will suffer from heavy computational as well
as storage cost.</p>
<p class="art-para">C. Wang et al <a href="#8" id="ref8">[8]</a> have proposed a scheme that downloads
top-k related files by using single keyword search. N. Cao and
W. sun <a href="#9" id="ref9">[9</a>,<a href="#10" id="ref10">10]</a> extended the secure keyword search to multikeyword search. Their styles will convert the words to vectors
list and will implement based on the matrix multiplications to
hide the real keyword from the cloud server. Xu et al <a href="#11" id="ref11">[11]</a> have
proposed multi-keyword ranked query over then crypted files
which enable a dynamic keyword index to avoid the ranking
order being inaccurate by some high frequency words. Li et al.
and Chuah et al. <a href="#12" id="ref12">[12</a>,<a href="#13" id="ref13">13]</a> have proposed fuzzy keyword search
over cloud files directing at acceptance of mutually slight
typos and arrangement inconsistencies for the data user's
search request.</p>
<p class="art-para">Wang et al <a href="#14" id="ref14">[14]</a> likewise proposed privacy guaranteed
similarity search method over encrypted cloud data. To
increase the search efficiency, they additionally construct a
multi way trie-tree for storage of similarity keywords.
Altogether the similar keywords in the trie-tree can be
efficiently placed in the depth-first search. The system
representations of earlier works only reflect one data owner,
where the data owner and data users can definitely
communicate and inter change secret information. When
many data owners are involved in the scheme, secret message
communication will create huge communication overhead.
This paper varies from earlier works for the prominence of
multi data owners in this scheme. This paper excellently
relaxes the necessities for data owners and data users, thus
our proposed scheme could be appropriate for a large
number of cloud users (Figure 1). Furthermore, performance
result shows that the proposed scheme is highly efficient and
reduced complexity. The initial works of Agrawal et al. <a href="#15" id="ref15">[15]</a>
have proposed an Order Preserving symmetric Encryption
system where the mathematical order of plain texts are saved.
Boldyreva et al <a href="#16" id="ref16">[16]</a> as a supplementary presented a flexible
order preserving encryption. These order preserving
encryption systems cannot be openly used in our proposed
scheme since we permit data owners to practice dissimilar
order preserving mappings to safeguard the privacy of their
relevance scores.</p>
<div class="art-img">
<img src="<?php echo $imgpath;?>images/mjbsb-101-f001.gif" class="img-responsive center-block"/></div>



<p class="art-para">To allow efficient search operation on the encrypted files
which is placed over the cloud, data owners initially construct
a secure searchable index on the keyword setmined from the
files. Then data owners encrypt their files <i>F</i> and acquire the
equivalent encrypted files <i>C</i>. Lastly together the encrypted
files as well as indexes are outsourced to the cloud. When an
authorized data user needs to search the keywords over the
encrypted files stored on cloud servers, the data user initially
computes the trapdoor <i>T</i> and submits it to the cloud. In our
system, every data owner will build their own index. The data
user will generate the trapdoor. Authenticated data user can
generate his trapdoor based on his required keywords. If the
trapdoor and the keyword match then the data user can
download the ranked results.</p>

<div class="art-img">
<img src="<?php echo $imgpath;?>images/mjbsb-101-n001.gif" class="img-responsive center-block"/></div>

<p class="art-para"><b>Keyword generation (Figure 2)</b><br/>
When the data user register towards the data owner to
access the files, after successful registration and authentication
the data user will receive the master secret key. Where is the
master secret key to decrypt the downloaded files. The term
refers to the public key of the data owner. The term refers to
identity number of the data user.</p>

<div class="art-img">
<img src="<?php echo $imgpath;?>images/mjbsb-101-f002.gif" class="img-responsive center-block"/></div>

<p class="art-para"><b>Trapdoor Generation (Figure 3)</b><br />
The data user will register himself towards the data owner.
The search keyword of the data user is . The data user uses the
hash function to have the secure search over the encrypted
files. Where mod n refers to the prime number selected by the
data user.</p>

<div class="art-img">
<img src="<?php echo $imgpath;?>images/mjbsb-101-f003.gif" class="img-responsive center-block"/></div>

<p class="art-para"><b>Data Owners keyword encryption (Figure 4)</b><br/>
The data owner will encrypt the files and place the files
over the cloud. For encrypting the files the data owner will
choose the random number s and the private key of the data
owner where <i>k</i> refers to the private key and <i>i</i> refer to the n
number of the data owners. Finally the data owner will submit
the encrypted files over the cloud.</p>

<div class="art-img">
<img src="<?php echo $imgpath;?>images/mjbsb-101-f004.gif" class="img-responsive center-block"/></div>

<p class="art-para"><b>Cloud matching the trapdoor and keyword (Figure 5)</b><br/>
When the cloud service provider receives the trapdoor
submitted by the data user and the keyword submitted by the
data owner, once if the trapdoor and the keyword matches
then the cloud will provide the ranked results to the data user.</p>

<div class="art-img">
<img src="<?php echo $imgpath;?>images/mjbsb-101-f005.gif" class="img-responsive center-block"/></div>


<p class="art-para"><b>Security Evaluation</b><br/>
<b>A. Man in the middle attack</b><br/>
The man in the middle attack is not possible since the
keyword is hashed and the search request is submitted
towards the cloud service provider. Without knowing the hashing algorithm the attacker cannot decrypt the file. Thus
man in the middle attack is impossible.</p>

<p class="art-para"><b>B. Impersonation attack</b><br/>
The data user will register towards the data owner. While
registering the data user will submit the identity of the data
user. The data owner using its public key will generate the
master secret key. So if the attacker impersonates like the
legal data user then without having the master secret key he
cannot decrypt the downloaded files.</p>

<p class="art-para"><b>Performance Evaluation</b><br/>The performance analysis section is implemented based
on the Python programming language on a PC with 3.2 GHZ
Pentium Dual Core CPU and memory: 2GB.</p>


<p class="art-subhead" id="conclusion">Conclusion</p>
<p class="art-para">In this paper, we resolve the problem of computation
complexity of secure multikeyword search for multiple data
owners also multiple data users in the cloud environment.
When compared to the earlier works, our scheme enables
authenticated data users to achieve secure and efficient
search over multiple data owners' files. To enable the cloud to
execute secure search among multiple owners' files encrypted
with different secret keys. We have developed a secure
trapdoor for having secure search over the cloud. We have
developed the data owner constructing the encrypted
keyword for the files collection. Moreover, we show that our
approach is computationally efficient even for large data sets
it also suit for large keyword sets.</p>


<p class="art-subhead" id="references">References</p>
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