  SEPAR is a lightweight cryptographic algorithm, designed to implement on
resource-constrained devices especially those employed in IoT environments.
Meanwhile, the mixed structure design of cipher leads to speed improvement
while guaranteeing its resistance against common cryptographic attacks,
especially differential and linear attacks. In order to confirm the resistance
of the cipher against differential attack, an extensive investigation was
presented in our previous work. In his study, we conduct new research
continuing the previously presented research. We prove that there are enough
active S-boxes so as to resist cipher against differential cryptanalysis.
Moreover, this can provide a tight bound of resisting cipher against this
attack.
