3) Existence of TTP: As shown in the Join algorithm, C only knows the Cred = (A, e) and public signing key xphid = (hx1,
hv2) of each SM, it has no idea about the private signing key xsk = (x, v). In the Data Upload algorithm, SM signs its message using xsk and Cred. Even the adversary has compromised C, it cannot get any private information about each SM. We can learn that the security of our PSMLAC is not based on the security of any TTP.