Notes on a group-oriented setting's multisigncryption scheme with threshold designcryption

Zhang et al. proposed recently a group-oriented multisigncryption scheme with threshold designcryption and affirmed that their scheme is secure under standard complexity assumptions. However, the note elaborates concrete attacks on its indistinguishability and unforgeability under their security models. We also provide the impossibility result of public ciphertext authenticity for the scheme.