ENCRYPTION DEVICE, DECRYPTION DEVICE, ENCRYPTION METHOD, DECRYPTION METHOD, PROGRAM, AND RECORDING MEDIUM

摘要

In encryption, a random number r is generated to generate a ciphertext C2 =M (+) R(r), function values Hs(r, C2), a common key K, a ciphertext C(Ψ+1) of the random number r using the common key K, and ciphertexts C(0) and C(λ) of the common key K that correspond to function values HS(r, C2). In decryption, a common key K′ is decrypted from input ciphertexts C′(0) and C′(λ), an input ciphertext C′(Ψ+1) is decrypted by using the common key K′ to generate a decrypted value r′, and function values HS(r′, C2′) is generated. If the input ciphertexts C′(0) and C′(λ) do not match ciphertexts C″(0) and C″(λ) of the common key K′ that correspond to the function values HS(r′, C2′), decryption is rejected; if they match, the input ciphertext C2′ is decrypted.