RE-ENCRYPTION DEVICE, CRYPTOSYSTEM, RE-ENCRYPTION METHOD, AND RE-ENCRYPTION PROGRAM

摘要

An encryption device (30) generates a session key K and a ciphertext cts in which the session key K is encrypted that were generated by an encryption algorithm using attribute information S as input. A re-encryption key generation device (40) generates a re-encryption key rk including: a converted decryption key skΓ~ generated by setting a random number r for a decryption key skΓ that can decrypt the ciphertext ctS; a session key K' and a ciphertext ctS' generated by the encryption algorithm using attribute information S' as input; and conversion information generated from the random number r. A re-encryption device (50) uses the conversion information to delete an element pertaining to the random number r from decryption information K^ obtained by decrypting the ciphertext ctS using the converted decryption key skΓ~, and outputs a re-encrypted ciphertext rctS' including an encryption element K~ that sets a session key K' and the ciphertext ctS'.