Patent ID: 9602278
Date: 2017-03-21
CPC Classifications: G06F,H04L

Claim:
1. An encryption device, comprising: a key calculation unit stored in a memory and configured to calculate a derived key by a calculation using a first hash function set in advance by taking a plain text as a numerical value and an identifier corresponding thereto as input values; a cipher-text-by-identifier generation unit stored in the memory and configured to generate a cipher-text-by-identifier acquired by encrypting the identifier by a calculation using the first hash function by taking the identifier and the derived key as input values; a relative value generation unit stored in the memory and configured to generate relative values e, e′ that are values used for a greater-than-and-less-than comparison assessment between the plain text and another plain text through performing a calculation using a second hash function set in advance and taking a modulo (mod) operation, by taking the derived key and the plain text as input values; a relative value cipher-text concealment unit stored in the memory and configured to generate a relative value cipher-text acquired by encrypting the relative value through a calculation using the second hash function and the modulo operation, by taking the derived key, the identifier, and the relative value as input values; and a cipher-text generating/outputting function unit configured to generate and output a character string constituted with the cipher-text-by-identifier and the relative value cipher-text as a cipher-text of the plain text, wherein: the cipher-text-by-identifier generation unit stored in the memory includes a function which, regarding an arbitrary integer k from 1 to n, generates a k-th block value of the cipher-text-by-identifier from the k-th block of the derived key and the identifier for a given integer n, and the relative value generation unit stored in the memory includes a relative value generating function which generates values of the k-th block corresponding to respective values of n-pieces of each data block sequence of the cipher-text-by-identifier as the relative values.