How to construct secure cryptographic location-based services

Recently, ubiquitous computing / networks have been studied actively. These networks provide services depending on real environments of mobile nodes. Especially, we expect location-based services (LBSs), which rely on location of mobile nodes, are anticipated to come into wide use in the future. High-value LBSs require cryptography to ensure security. Here, cryptographic LBSs comprise a key management function (e.g. key sharing with nodes) and a location management function (e.g. location verification of nodes). Cooperation between key and location management functions realizes cryptographic LBSs. However, these functions have mostly been studied individually. This study indicates that cryptographic LBSs are insecure if the cooperation is incomplete, and proposes a method of constructing secure cryptographic LBSs.