Group Public Key Encryption with Equality Test Against Offline Message Recovery Attack

Abstract Public key encryption with equality test (PKEET) allows a tester to check whether two ciphertexts encrypted under different public keys contain the same message without decrypting them. In this paper, we first introduce group mechanism into PKEET and propose a new primitive, namely group public key encryption with equality test (G-PKEET). G-PKEET can resist the attack that the tester can recover the message from a given ciphertext by exhaustively guessing the message offline. Furthermore, the group mechanism makes PKEET supporting group granularity authorization, which could authorize a tester to perform the equality test only on ciphertexts of group users, and could greatly reduce not only the storage cost of trapdoors but also the cost of computation and communication. We define security models for G-PKEET, present its concrete construction in bilinear pairings and prove its security in the random oracle model.