Wednesday, 23 July 2014

Privacy-Preserving and Content-Protecting Location Based Queries

In this paper we present a solution to one of the location-based query problems. This problem is defined as follows: (i) a user wants to query a database of location data, known as Points Of Interest (POI), and does not want to reveal his/her location to the server due to privacy concerns; (ii) the owner of the location data, that is, the location server, does not want to simply distribute its data to all users. The location server desires to have some control over its data, since the data is its asset. Previous solutions have used a trusted anonymiser to address privacy, but introduced the impracticality of trusting a third party. More recent solutions have used homomorphic encryption to remove this weakness. Briefly, the user submits his/her encrypted coordinates to the server and the server would determine the user’s location homomorphically, and then the user would acquire the corresponding record using Private Information Retrieval techniques. We propose a major enhancement upon this result by introducing a similar two stage approach, where the homomorphic comparison step is replaced with Oblivious Transfer to achieve a more secure solution for both parties. The solution we present is efficient and practical in many scenarios. We also include the results of a working prototype to illustrate the efficiency of our protocol.
 The first solution to the problem was proposed by Beresford, in which the privacy of the user is maintained by constantly changing the user’s name or pseudonym within some mix-zone. It can be shown that, due to the nature of the data being exchanged between the user and the server, the frequent changing of the user’s name provides little protection for the user’s privacy. A more recent investigation of the mix-zone approach has been applied to road networks. They investigated the required number of users to satisfy the unlinkability property when there are repeated queries over an interval. This requires careful control of how many users are contained within the mix-zone, which is difficult to achieve in practice. A complementary technique to the mix-zone approach is based on k-anonymity. The concept of kanonymity was introduced as a method for preserving privacy when releasing sensitive records. This is achieved by generalisation and suppression algorithms to ensure that a record could not be distinguished from (k 1) other records. The solutions for LBS use a trusted anonymiser to provide anonymity for the location data, such that the location data of a user cannot be distinguished from (k 1) other users.
·       As solutions based on the use of a central anonymiser are not practical.
·       This incurs both processing and communication overhead for the user device.
In this paper, we propose a novel protocol for location based queries that has major performance improvements with respect to the approach by Ghinita. Like such protocol, our protocol is organized according to two stages. In the first stage, the user privately determines his/her location within a public grid, using oblivious transfer. This data contains both the ID and associated symmetric key for the block of data in the private grid. In the second stage, the user executes a communicational efficient PIR, to retrieve the appropriate block in the private grid. This block is decrypted using the symmetric key obtained in the previous stage. Our protocol thus provides protection for both the user and the server. The user is protected because the server is unable to determine his/her location. Similarly, the server’s data is protected since a malicious user can only decrypt the block of data obtained by PIR with the encryption key acquired in the previous stage. In other words, users cannot gain any more data than what they have paid for. We also provide
results from a working prototype showing the efficiency of our approach.
·       This idea was extended to provide database protection.
·       PIR is used to retrieve the data contained within the appropriate cell.
·       It is more efficient.




ü Processor                  -        Pentium –IV

ü Speed                        -        1.1 Ghz
ü RAM                         -        512 MB(min)
ü Hard Disk                 -        40 GB
ü Key Board                -        Standard Windows Keyboard
ü Mouse                       -        Two or Three Button Mouse
ü Monitor                     -        LCD/LED


         Operating system :         Windows XP
         Coding Language :         Java
         Data Base             :         MySQL
         Tool                     :         Net Beans IDE


Russell Paulet, Md. Golam Kaosar, Xun Yi, Elisa Bertino, Privacy-Preserving and Content-Protecting Location Based Queries IEEE TRANSACTIONS ON KNOWLEDGE AND DATA ENGINEERING, 2012 IEEE 28th International Conference on Data Engineering.

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