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.