Abstract: Public key encryption with equality test(PKEET) is a public key encryption scheme which allows testers to perform equality tests on ciphertexts without holding corresponding private keys, that is, detecting whether the plaintexts decrypted from given cyphertext are equal. The fine-grained authorization PKEET (FG-PKEET) and PKEET with flexible authorization (PKEET-FA) schemes mentioned in previous works improve the functionality of PKEET in aspect of authorization granularity: FG-PKEET scheme allows one user to interact with another user to generate a token specifically for detecting the equality of all these two users’ ciphertexts, while PKEET-FA scheme extends the type of authorization object of the token from user level to ciphertext level, permitting one user to authorize on a specific ciphertext. Both solutions have their own application scenarios and do not include each other in terms of functionality. Thus we propose flexible fine-grained authorization PKEET scheme. Our scheme obtains security properties related to adaptive ciphertext attack and fine-grained authorization. Our solution combines both fine-grained authorization and flexible fine-grained features, allowing two users to authorize respectively on one specified ciphertext or all his ciphertexts. Meanwhile, comparing to existing PKEET schemes with fine-grained authorization or flexible authorization features which rely on random oracle model, our scheme’s security properties are proved under standard model.

Key words: public key encryption, equality test, standard model, fine-grained authorization, adaptive chosen ciphertext attack