($I$) are leaky. So, periodically changing TRN ($S$) and sending through side-channel resistant ciphers re-intensify the security of the communication.

Based on the size of the CSTN/RCSTN (number of I/O), we will show that the maximum feasible update frequency ($N$) would be changed. Consequently, the CSTN configuration (TRN), which is fed by RNG, must be changed dynamically after every $T$ iterations, where $T < N$. Also, the size of CSTN/RCSTN determines the number of configuration bits (size of each $S$) must be generated by the RNG. In the following sub-sections we discuss the details of *ExTru* implementation.

Configurable Switching & Toggling Network (CSTN) {#CSTN_section}
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The CSTN is a logarithmic routing (permutation) network that could permute the order of the signals at its input pins to its output pins while possibly toggling their logic levels based on its configuration (TRN). Fig. \[CSTN\_arch\](a) captures a simple implementation of an 8$\times$8 CSTN based on *OMEGA* network [@ahmadi1989survey]. The network is constructed using permutation elements, denoted as Re-Routing Blocks (RRB). Each RRB is able to possibly toggle and permute each of the input signals to each of its outputs. The number of RRBs needed to implement this simple CSTN for $N$ inputs ($N$ 