KEY RESTORING METHOD AND PROGRAM RECORDING MEDIUM

摘要

PROBLEM TO BE SOLVED: To mitigate the processing of a key restoration engine. SOLUTION: A user A has an open key Kap and a secret key Kas and a key restoration engine 11 has an open key Krp and a secret key Krs. A key storage engine 12 generates the key K of the user A by using a password system for generating same common information Kra with Kap and the Krs or with the Kas and the Krp. The engine 11 ciphers the K with the Kra and an engine 13 stores a [K]Kra. The engine 11 obtains the [K]Kra from the engine 13 by a key restoration request from the A and transfers it to the A. The A generates the Kra from the Krp and the Kas, and the [K]Kra is decoded with the Kra and the K is obtained.