To prevent information leakage at the time of transferring secret information data stored by using secret sharing scheme to the outside.;Data to be transferred to a delivery destination of secret information data is divided into a plurality of data pieces by using the secret sharing scheme, and a part of the data pieces is stored in a portable storage medium by a data delivery source and is delivered to the data delivery destination by means such as a package delivery service. A computer at the data delivery destination accesses a predetermined website to download the other data pieces. A computer at the data delivery destination restores the original secret information data from the data pieces obtained via such two kinds of routes.
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