To reproduce restricted data for an entity itself if the entity forgets only a portion of the restricted data, or by obtaining cooperation of other entities if the entity forgets a major portion of the restricted data.

A sequence of restricted data over a plurality of entities is regarded as an information part of a product code, each row is defined as a plurality of pieces of restricted data of each entity, and each column is defined as a column of restricted data over a plurality of entities. A check symbol with a linear code to each row and a check symbol with a linear code to each column are stored. If the entity forgets only a portion of the restricted data, reproduction is performed by using the check symbol (check symbol to self- restricted data) in each row, and if the entity forgets a major portion of the restricted data, cooperation from other entities is obtained to reproduce the restricted data by using the check symbol to each column.