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

摘要

An encryption device calculates a derived key by taking a document as a numerical value and corresponding identifier as input values and generates a cipher-text-by-identifier acquired by encrypting the document through a calculation taking the documents as input values, and a comparison unit generates relative values used for a greater-than-and-less-than comparison assessment between the plain text and another plain text through a calculation using a second hash function taking the derived key and plain text as input values; generates a relative value cipher-text through a calculation taking the derived key, the identifier, and the relative value as input values; generates a character string constituted with the cipher-text-by-identifier and the relative value cipher-text as a cipher-text; restores the relative values corresponding to the different cipher-texts through calculations using the second hash function; and performs a greater-than-and-less-than assessment on the encrypted different plain texts through a greater-than-and-less-than comparison on the relative values.