ENCRYPTION DEVICE, CIPHER-TEXT COMPARISON SYSTEM, CIPHER-TEXT COMPARISON METHOD, AND CIPHER-TEXT COMPARISON PROGRAM

摘要

[Problem] To perform a greater-than-and-less-than comparison for different pieces of numeric data which have each been encrypted. [Solution] This invention is provided with: an encryption device (510) which treats a numerically represented document and an identifier for the same as input values in order to calculate a derived key, and which, by way of a calculation which treats the identifier and the document as input values, generates a cipher-text-by-identifier, in which the document has been encrypted; and a comparison unit (513). The comparison unit (513), by performing calculation using a second hash function which treats the derived key and plain text as input values, generates a relative value which is a value for greater-than-and-less-than comparison assessment between the plain text and another plain text. In addition, using a calculation which treats the derived key, the identifier, and the relative value as input values, a relative value cipher-text, in which the relative value has been encrypted, is generated, and a character string, comprising the cipher-text-by-identifier and the relative value cipher-text, is generated as a document cipher-text. When the other cipher-text and an identifier corresponding thereto are input, using calculation by way of the second hash function, relative values corresponding to each of the different cipher-texts are restored, and by performing a greater-than-and-less-than comparison for the relative values therefor, a greater-than-and-less-than comparison assessment for the encrypted different plain texts is performed.