Encryption apparatus, decryption apparatus, decryption-possible verification apparatus, cryptosystem, encryption method, and computer readable medium

Abstract

An encryption unit () that an encryption apparatus () includes, when a user secret key SKΓ is generated using a secret key MSK of attribute based encryption and a set of attributes Γ corresponding to a decryption-possible condition L, generates a key K and a ciphertext P corresponding to the key K by encrypting the decryption-possible condition L using, as an encryption key of the attribute based encryption, a key PK consisting of a public key MPK corresponding to the secret key MSK and a public key PQCPK of post quantum cryptography, regards a part of the ciphertext P where the decryption-possible condition L is encrypted based on a secret value as P-D, regards a part of the ciphertext P where the secret value that is shared is encrypted as P-SS, and generates K' and P′-D by randomizing each of the key K and the P-D using a random number R, and generates a ciphertext C by encrypting data consisting of the P-D and the random number R using the public key PQCPK. Here, the P-SS, the P′-D, and the K′ are decryption-possible verification parameters corresponding to the user secret key SKΓ.