Provably convertible multi-authenticated encryption scheme for generalized group communications

In 2008, Wu et al. proposed a convertible multi-authenticated encryption (CMAE) scheme based on discrete logarithms. To improve the computational efficiency of Wu et al.'s scheme, Tsai proposed another CMAE scheme without using message redundancy. These CMAE schemes, however, might be inadequate for group-oriented applications. In the same year, Chang presented a CMAE scheme using message redundancy for group communications [published in Information Sciences 178 (17) (2008) 3426-3434]. In his scheme, multiple signers of the same group can cooperate with each other to generate a valid authenticated encryption signature for a designated verifying group with access structured multiple verifiers. In this paper, we propose a new convertible multi-authenticated encryption scheme without using message redundancy for generalized group communications. Multiple signers of the signing group can cooperate with each other to generate a valid authenticated encryption signature for a verifying group with access structured multiple verifiers. The verifiers in the same access structure can cooperatively recover and verify the signing group's signature. In case of a later dispute, any participant verifier can convert the authenticated encryption signature into an ordinary one. As compared with previous works, our proposed scheme is more efficient in terms of computational efforts and communication overheads.