Method of a public key encryption and a cypher communication both secure against a chosen-ciphertext attack

摘要

The public-key encryption method uses the sender-side apparatus (100) by the creator of a ciphertest and creates the ciphertext (y1, y2) of a plaintext x (∈{0, 1}n) in y1 = f (x0klG(r)), y2 = H (x0k1G(r))r with respect to the published trapdoor-equipped unidirectional function f and the random functions G, H. Meanwhile, the receiver of the ciphertext, who has received the ciphertext by the receiver-side apparatus (200) via the communications line (300), performs the decryption processing with the use of f-1, i.e., the secret key, in accordance with the steps inverse to those of the encryption processing.