| 摘要 |
PROBLEM TO BE SOLVED: To enable a user to normally and surely decode enciphered information by demanding transmission of a second key, when a decoding means cannot decode a first key. SOLUTION: This device is equipped with a decoding means (a decoding unit) 91 for decoding a first key by a second key and a demanding means (a communication part) 61 for demanding the second key, when the decoding means 91 cannot decode the first key. This communication part 61 communicates with a service provider 3 or an EMD service center 1 via a network 4, receives or transmits specified information. Also, a decoding unit 91 of a decoding/ enciphering module 74 decodes an enciphered contents key Kco by a distribution key Kd and outputs it to an enciphering unit 93. Thus, the first key is decoded by the second key and, when it cannot be decoded, transmission of the second key is demanded; so that even if a data provision side changes a key in an arbitrary timing, a user can normally and surely decode enciphered information.
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