## 3 The Proposed IoMT Model
### Secure Data Transmission and Storage
A total of 100 sequences of random 128-bit plaintext blocks and keys were used to prepare the SKAC and SPAC matrices. A total of 12 and 800 different keys and plaintext block inputs were respectively used to test the strict key avalanche criterion (SKAC) and strict plaintext avalanche criterion (SPAC) of HMCC. 7. **Comparative Security Analysis of the HMCC with Existing Ciphers** A comparative analysis of HMCC with the existing symmetric ciphers in the literature was carried out. Two of the most widely documented block ciphers, namely DES and AES, were experimentally compared with HMCC. Information entropy, autocorrelation analysis, strict avalanche criterion, and NPCR and UACI values of differential cryptanalysis were used as parameters for the comparative analysis. ## 4 Results and Discussion

In this section, experimental results on the security analysis of the proposed IoMT model are discussed. Security analysis, encryption/decryption time analysis, and comparative security analysis with the existing systems are discussed. ### Results of Security Analysis

1. **Man-in-the-Middle, replay, and denial-of-service attacks**: An attacker in MIMA is capable of impersonating both the sender and receiver [63]. If this attack succeeds, the attacker can send information to the receiver and also respond to the sender. An attacker in MIMA is also capable of resending the original message sent by a legitimate node to deceive the receiver. The activities of a MIMA attacker can also lead to denial-of-service attacks if such an attacker decides to regularly transmit false signals to deny authorized network users access to resources or services to which they are entitled. The proposed scheme is resistant to MIMA attacks of any form. A MIMA attacker that intercepts messages being transmitted between a client and the healthcare centre does not have enough information to compute a shared secret key between the two because it depends on the private keys of both,which were not shared. Because the delivered message contains a timestamp T that identifies the precise instant when the message was sent, a MIMA attack that resolves to engage in replay assaults will fail. This establishes the timing difference used to identify any attack during the replay phase. A MIMA attacker who resolves to launch denial-of-service attacks is incapacitated because the attacker needs a shared secret key to encrypt the data, which is only possible through stealing IDs or becoming a legitimate user. 2. **Analysis of Encryption algorithm of HMCC:** Table 3 shows plaintext samples and the corresponding resulting ciphertexts when plaintexts are submitted to the HMCC encryption technique. According to the results in Table 3, all repetitive terms are omitted from the ciphertext, and it is difficult to verify from ciphertext only the characters in the plaintext that are repeated. As a result, using repetitive phrases in plaintext provides no useful information to the cryptanalysts to attack HMCC. * **Spectral Frequency Analysis of Modified Caesar Cipher:** The result of the frequency analysis of the plaintexts and their corresponding ciphertexts are given in Table 4 labelled serial number 1-3, and the frequency analysis of the sampled plaintexts and the corresponding obtained ciphertexts are respectively shown by the histograms in Figures 4-6. Figure 4 shows the histograms of the plaintext and ciphertext in S/N 1 of Table 4. From Figure 4, it can be seen that the frequency of the characters of the plaintext is not uniform, while the frequency of the ciphertext characters is relatively uniform. This characteristic reveals that HMCC is resistant to frequency analysis attack. Figure 5 shows the histograms of the plaintext and ciphertext in S/N 2 of Table 4. From Figure 5, it can be seen that the frequency of the characters of the plaintext is not uniform. However, the frequency of the ciphertext characters is uniform. This result confirms the fact that attackers cannot use frequency analysis of the ciphertext to obtain any useful information about the plaintext.