| 摘要 |
PROBLEM TO BE SOLVED: To recognize the relationship between electronic data and individual/ institution with a high reliability by extracting genuine confirmation information which is buried into a mark that is pasted on a Web page having a watermark as a digital watermark. SOLUTION: A control section 112 controls a signature verifying section 114, decodes an extracted electronic signature by a verifying key 122 of an arbitrary purchase stored in a storage section 120, compares the decoded value and an hash value obtained by evaluating the contents of an original stored in the section 120 using a one directional hash function, that is same as the one being used by a purchaser device 200, and verifies the signature. Note that the rule, in which the electronic signature is buried into the contents by the device 200, is made secret for the parties other than a provider. If the hash value, which is used to evaluate the contents of the original, and the value of an electronic signature, that is reconstructed, do not agree with each other, the electronic signature extracted from an unauthorized copy using the verifying key of an another purchaser is decoded and the agreement between the decoded signature and the hash value of the contents of the original is verified. |
