New identity-based key-insulated convertible multi-authenticated encryption scheme

Elaborating on the merits of convertible multi-authenticated encryption (CMAE) schemes and key-insulated systems, we propose a novel identity-based key-insulated convertible multi-authenticated encryption scheme (IB-KI-CMAE), which can effectively reduce the impact caused by the key exposure. Our scheme allows each user to periodically update his private key while the corresponding public one remains unchanged. Additionally, a group of signers can cooperatively generate an authenticated ciphertext such that only the designated recipient has the ability to decrypt the ciphertext and verify their signature. In case of a later dispute over repudiation, the designated recipient can easily reveal the converted multi-signature for public arbitration. Our scheme can bring crucial benefits to the applications such as joint account and business contract signing. Moreover, in the random oracle model, we also formally prove that the proposed scheme achieves the security requirement of confidentiality against indistinguishability under adaptive chosen-ciphertext attacks (IND-CCA2) and that of unforgeability against existential forgery under adaptive chosen-message attacks (EF-CMA).