3) When a SM is broken, and it sends multiple messages in a time period, C can effectively find out this failure SM. In the Data Upload algorithm, we can observe that T2 = H2(T)x, where x is the private key of a SM.When a SM is broken, and it sends multiple signatures in a same time interval, then the x and T of these signatures are the same. As a result, the T2 of these signatures are also equal. Then, C can successfully link these signatures that come from a same SM in a time period. After that C asks each SMi to prove that it has not sent these linked signatures. As shown in the Trace algorithm, each SMi is requested to make zero knowledge proof. As the zero-knowledge proof is sound, the broken SM cannot
convince C that it has not sent these messages. Because the zero-knowledge property of zero-knowledge proof,
C cannot learn any secret information of the valid SM.