Key Sensitivity Analysis

The employed key for the encryption scheme is considered highly sensitive when the encrypted message cannot be recovered, as a slight difference in one of the key components would result in an incorrect decrypted ciphertext. Therefore, we hereby investigate the key sensitivity of the proposed secure communication scheme, as shown in Figure 15. In this figure, a signal has been encrypted by *k*1, and using the same key, we could recover the signal, as shown in Figure 15a–c. However, when we change the 14th decimal place in the parameters, or initial conditions, or both to obtain three other keys, namely, *k*2, *k*3, and *k*4, respectively, Figure 15d–f demonstrates that these keys fail to recover the original signal, which means that the proposed communication system has a robust and sensitive key.

**Figure 15.** Key sensitivity analysis: (**a**) the original signal; (**b**) the encrypted signal; (**c**) the decrypted with the right key (*k*1); (**d**–**f**) the decrypted signal with the wrong keys (*k*2, *k*3, *k*4), in which the change occurred slightly in the parameters and initial conditions, only the parameters, and only the initial condition, respectively.
