| 摘要 |
PROBLEM TO BE SOLVED: To determine incorrect partial decoding information in plural pieces of partial decoding information, with small computational complexity at a high speed. SOLUTION: A restoration terminal 20 receives partial decoding information which is generated by each of different distribution keys corresponding to secret keys and corresponds to each of the distribution keys, from a decoding server 50. The restoration terminal 20 generates a second plain text using the received plural pieces of partial decoding information and at least one element of a public key composed of a plurality of elements. The restoration terminal 20 generates a second ciphertext using the second plain text and at least one element of the public key composed of a plurality of elements. When the second ciphertext matches at least part of the first ciphertext, the restoration terminal 20 determines that a plain text can be restored using the plural pieces of partial decoding information, and in other cases it determines that the whole of the plural pieces of partial decoding information is invalid. COPYRIGHT: (C)2009,JPO&INPIT
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