Technologies of cloud computing that provide users with various services using computing resources existing on networks have recently been used. One example of such cloud computing technologies could be a technology in which an information processing device on a network collects various numerical information associated with a user, such as position information and biometric information, and provides the user with services in accordance with a comparison result and an analysis result of the collected numerical information. For example, there may be a technology in which an information processing device on a network collects and compares position information on a user and taxi vehicles, and provides the user with information on a taxi vehicle located in proximity to the user.
As such, when an information processing device collects and analyzes numerical information associated with a user, it is possible to provide services regardless of computing resources on the user's side. This improves convenience for the user. When an information processing device on a network collects numerical information associated with a user, however, it is preferable from the viewpoint of security that the numerical information be concealed so as not to leak to a third party. As the technology for concealing numerical information associated with a user, a concealment technology using masking is known.
For example, a terminal device used by a user and a terminal device mounted in a taxi vehicle conceal numerical information indicating the current locations using a predetermined mask value and send the concealed numerical information to an information processing device on a network. Then, the information processing device on a network collects the pieces of concealed numerical information from the user and the taxi vehicle and compares the pieces of collected numerical information with each other, thereby determining the proximity between the user and the taxi vehicle. Note that “Privacy-preserving Data Mining” Jun Sakuma, Interdisciplinary Graduate school of Science and Engineering, Tokyo Institute of Technology, Shigenobu Kobayashi, Interdisciplinary Graduate school of Science and Engineering and Tokyo Institute of Technology, for example, discloses the determining method concerned.