Encryption device, decryption device, encryption method, decryption method, and computer readable medium

Abstract

An encryption device divides a plaintext M to generate a value M[1], . . . , and a value M[m]. The encryption device generates an n-bit value B[i] by encrypting a value B[i−1] by a block cipher with a value T[i−1] as a key, for each integer i of i=1, . . . , m in ascending order, generates a value C[i] from the value B[i] and a value M[i], and generates an n-bit value T[i] from a value P(T[i−1]) obtained by converting the value T[i−1] using a replacement function P, a value F(B[i]) obtained by converting the value B[i] using a replacement function F, and the value C[i]. The encryption device generates a ciphertext C by connecting the values C[i] for i=1, . . . , m. The encryption device generates from a value H[m] and the value B[m], an authenticator Tag for detecting an alteration of the ciphertext C.