must be used to recover the permuted/toggled + substituted plaintext. We will show that similar to ACORN that engages only one hardware module for both encryption/decryption, the CSTN hardware is the same for both receiving/sending operations (same hardware for both CSTN and RCSTN). Hence, no duplicated hardware (one for CSTN and one for RCSTN) is required to be added on each side. When TRN is received from the transmitter it must be decrypted using the authenticated cipher to be used as the configuration of the RCSTN. If the received data is not TRN, it first must pass the s-box to accomplish re-substitution, then it must pass the RCSTN to recover the plaintext.

Fig. \[expdyn\] depicts the overall structure of dynamic encryption provided by *ExTru*, which has no sign of leaky communication. As shown in Fig. \[expdyn\](b), for each specific number of transmission ($T$), which must be less than $N$, a new CSTN configuration will be sent via side-channel resistant cipher. As it is shown, a secure message ($S$), which contains TRN, will be sent periodically after every $T$ messages ($I$) that are handled by CSTN/RCSTN. Based on different forms of attacks, such as side-channel, scan-based SAT, and algebraic attack, messages 