Development of Methods for Securing Spatial Information to Protect
Personal Sensitive Data While Preserving Spatial and Statistical
Relationship

Graduate School of Engineering, the University ofTokyo Professor
Yasushi Asami

1SummaryTwo major research topics are pursued in this project: (1) Method for securing spatial
information by adding noise after acquiring spatial information; (2) Method for securing
spatial information at the time of acquiring spatial information. Major results of both
topics are summarized in the following.
1. Method for securing spatial information by adding noise after acquiring spatialinformationA new method is developed for adding noise to the objective variable in regression
analysis, which is a sensitive information as a personal information. The degree ofperturbation by noise addition can be controlled by a single parameter, which eases
practical application.
In the proposed method, t-values of regression coefficients and coefficient ofdetermination are preserved. By applying this method to actual real estate data,
numerical experiments are conducted with adding noise to the real estate price as theobjective variable. The parameter value is derived such that the result of regression
analysis for perturbed data is not significantly different from that using only limited
portion of the data. As a result, an appropriate value of parameter is derived satisfying
both a sufficient perturbation of objective variable to conceal the original value and stillpreserving the statistical results.
2. Method for securing spatial information at the time of acquiring spatial
information
Two methods are developed to securing sensor acquired spatial data before storingthem into a server. One method is to securing spatial data while transmitting throughcommunication system. In the wireless multi-hop sensor networks, data are acquired onnodes and transmitted to sink-node, which is the boundary point with the external
network. To take advantage of this particular feature of transmission to secure data, amethod is devised such that data are sliced, i.e., partitioned into several parts andtransmitted to the sink node while mixing the sliced data in the relay nodes. The othermethod is to add noise at the point of sensing the spatial data. The method of negative
survey is extended so that it is applicable to continuous and correlated
multi-dimensional data. In this method, noise addition operation is done in the sensor
nodes, hence users who do not trust telecommunication carriers and administrativeorganization can participate in sensing. Hence this method enables acquiring sensitive
questionnaire survey, which contributes enriching quality and sorts of spatial data.
2Secret sharing scheme is a method to enable concealment calculation keeping the input
information secret. A new method to reduce memory space for distributed informationand to securing calculation operation. In addition, useful applications are developed for
medical system and recording life-log. Traditionally, concealment multiplication
requires more servers than concealment addition and subtraction. A method isdeveloped so that multiplication can be done with the same number of servers. The new
method is compared to traditional methods in terms of detailed performance.

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