Page 106 - Read Online

Salmani et al. J Surveill Secur Saf 2020;1:79–101 I http://dx.doi.org/10.20517/jsss.2020.16 Page 99

Nevertheless, all these methods suffer from private information leakage such as access pattern, search pattern,
and co-occurrence information leakage. Cao et al. [9] believe that, to solve this problem, we must “touch” the
whole outsourced dataset, which ends in losing the efficiency so other investigators chose not to impede these
leaks which kept them out of the designed goals.

8 CONCLUSIONS
The problem of leakless preserving privacy multi-keyword ranked search in SSE schemes, addressed here. We
built a private model to prevent two kinds of leakage: search pattern and co-occurrence private information
leakage. We employed the asymmetric inner-product to calculate the relevance score of each document with
respect to the query. We also introduced our chaining encryption notion to generate multiple ciphertexts
for the same keyword. All this leads to more uncertainty and a uniform probability model for the keywords
distribution. Furthermore, with our chaining encryption notion, the data user is able to randomly choose a
portion of the ciphertexts for each keyword. Thus even if consecutive queries share some keywords, the cloud
is not able to find a pattern between the queries due to using different versions of ciphertexts in each query.
Moreover, co-occurring terms appear with different ciphertexts in the encrypted documents, and so, finding
the co-occurring terms becomes significantly more difficult for the cloud. Next, to tackle the challenge of
leakless multi-keyword ranked search, we propose the LRSE scheme and define the privacy requirements. In
addition, we explain each level of the LRSE scheme in details and describe the required algorithms.

Furthermore, we performed the security and privacy analysis to show the efficiency of our proposed approach.
We proved the the novel chaining notion and consequently LRSE is secure and compared complexity of our
proposed scheme with related work in various criteria such as server computation, communication, etc. Look-
ing to the future, we will modify LRSE to prevent access pattern attack.

DECLARATIONS
Authors’ contributions
Each author contributed equally to the paper.

Availability of data and materials
Not applicable.

Financial support and sponsorship
This research is partly supported by the Natural Sciences and Engineering Research Council of Canada.

Conflicts of interest
All authors declared that there are no conflicts of interest.

Ethical approval and consent to participate
Not applicable.

Consent for publication
Not applicable.

Copyright
© The Author(s) 2020.