## 3 The Proposed IoMT Model
### Secure Data Transmission and Storage
Figure 6 shows the histograms of the plaintext and ciphertext in S/N 3 of Table 4. From Figure 6, it can be seen that the frequency of the single character of plaintext has been spread uniformly over several characters in the ciphertext obtained from HMCC such that it cannot be determined from the ciphertext that the plaintext contains the same character. This result also confirms that HMCC is resistant to frequency analysis attacks. \begin{table}
\begin{tabular}{c c c} \hline \hline
**S/N** & **Plaintext** & **Encrypted Text from HMCC** \\ \hline \multirow{4}{*}{\(1\)} & **Plaintext**: [PERSON] is good all the time. Great & **Ciphertext**: \(\text{hy95}\times\text{\text{\text{\text{\text{\text{\text{\text{\text{ \text{\text{\text{\text{\text{\text{\text



Figure 4: Histogram of the frequency of (**a**) sample plaintext and (**b**) ciphertext in Table 4 S/N 1. Figure 5: Histogram of the frequency of (**a**) sample plaintext and (**b**) ciphertext in Table 4 S/N 2. As can be seen from the sample outputs in Figures 4-6, the histograms show that the frequencies of the characters of the ciphertext are uniform. Where the plaintext contains the same characters, the ciphertext produced by HMCC spreads the frequency of the plaintext character over several characters uniformly. A cipher that is capable of producing ciphertext that has a relatively uniform frequency of characters is said to be resistant to frequency analysis attack. Hence, HMCC cannot be broken by applying a frequency analysis attack. A cipher that is resistant to differential assaults is one that causes a larger percentage of modification in ciphertext characters due to modest variations in plaintext characters [64]. The ideal values of NPCR and UACI are, respectively, 99.6093% and 33.4635% for a cipher that is resistant to differential cryptanalysis attack [65]. Whereas the NPCR and UACI fluctuate with secret keys, the values of NPCR and UACI from the samples provided in Table 5 reveal that HMCC is immune to differential cryptanalysis attack since in both samples, 100% of the ciphertext characters are altered due to a change in one character of plaintext. The values of UACI obtained in both cases are also very close to the standard 33.46%. This result shows that HMCC is not vulnerable to differential cryptanalysis attacks. The ciphertext entropy value (7.9773) is very closed to the expected entropy value (8). This result shows that the HMCC cipher's diffusion mechanism is strong. Any cipher with an effective diffusion property certifies that when a plaintext is encrypted, all of its symbols are transformed. Any cipher with an ineffective diffusion property will result in the ciphertext having numerous indistinguishable symbols, making the cipher vulnerable to entropy attack. As a result, HMCC is immune to information entropy analysis. * **Autocorrelation Analysis of HMCC:** The autocorrelation function is used to define the resemblance of two sequences. Cryptanalysts use autocorrelation to calculate secret key length in classical ciphers. A cipher that is resistant to autocorrelation attacks produces ciphertext that has more uniform and lower autocorrelation than plaintext. Figure 7 depicts the graph of the autocorrelation of a sample of plaintext and the autocorrelation of the ciphertext generated after the sample plaintext was encrypted using the HMCC cipher. The graphs of autocorrelation of plaintext and ciphertext in Figure 4 indicate that ciphertext autocorrelation is uniform and lower than plaintext autocorrelation. A cipher that produces ciphertext whose autocorrelation is uniform and lower than the autocorrelation of the plaintext from where it is produced is said to be resistant to autocorrelation attacks. Going by the autocorrelation analysis result of the ciphertext produced, it can be said that HMCCC is immune to autocorrelation cryptanalysis attacks. \begin{table}
\begin{tabular}{c c} \hline \hline
**Text Type** & **Entropy** \\ \hline Plaintext & 4.5009 \\ Ciphertext & 7.9773 \\ \hline \hline \end{tabular}
\end{table}