| 摘要 |
PROBLEM TO BE SOLVED: To secrete a retrieving expression and performs 2-pass encoding in a retrieval phase. ! SOLUTION: In a storage phase, first to N-th cipher keywords encrypted by a keyword encryption unit are arranged in columns, first to M-th cipher files encrypted by a file encryption unit are arranged in rows, and a table having encryption indices arrayed in a matrix of M rows and N columns and encrypted by an index encryption unit is transmitted from a user terminal to a server and preserved in the server. In a retrieval phase, the user terminal transmits first and second cipher retrieving keywords which are encrypted by a retrieving keyword encryption unit, a new counter value obtained by incrementing a counter value by one, first to M-th encryption retrieving expressions, which are encrypted by a retrieving expression encryption unit, to the server, and acquires a set of retrieved cipher files. The retrieving expression encryption unit uses the first and second retrieving keywords, a cipher key, |
