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encrypted, thereby increasing overhead for the update
query.
Many researchers have investigated the problem
of keywords searching on encrypted data using either
symmetric encryption (Song et al., 2000), asymmet-
ric encryption (Boneh et al., 2004) or a combination
of symmetric, asymmetric encryption and hash func-
tions (Dong et al., 2008). In spite of security vul-
nerabilities (like statistical attack (Song et al., 2000))
and significant overhead (Boneh et al., 2004; Dong
et al., 2008), these encryption schemes are possibly
useful in searching for keywords in a file, document
or email. However, these solutions can not be applied
to the problem of efficiently querying encrypted re-
lational databases. Especially, we discuss in this pa-
per the problem of encrypting integer data, executing
range queries and implementing relational operations
over encrypted database.
9 CONCLUSIONS
We propose a novel order preserving encryption
scheme (MV-POPES) that is robust against known
plaintext attack and statistical attack. In MV-POPES,
we change the order of the plaintext values by por-
tioning the domain into many partitions and assign a
unique random number to each partition that repre-
sents the order in the encrypted domain. MV-POPES
allows one integer to be encrypted to many different
values using the same encryption key. It also pre-
serves the order of the integer values within each par-
tition to allow comparison operation to be directly
applied to the encrypted data. We have developed
techniques so that most processes in executing SQL
queries can be done on encrypted databases. In some
cases, a small amount of work to filter false positives
or perform relational operations is needed on the de-
crypted data. Experiments on MV-POPES showed
that security for sensitive data can be achieved with
reasonable overhead, confirming the feasibility of the
scheme. In the future, we will investigate the opti-
mal algorithm for domain partitioning that minimize
performance overhead in query processing and ensure
high privacy. We also plan to study the encryption of
non-integer data such as strings.
ACKNOWLEDGEMENTS
This research has been supported in part by the
Graint-in-Aid for Scientific Research from MEXT
(#21013004) and Grant-in-Aid for Young Scientists
(B) (#21700093) by JSPS.
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