## 2 Related Work  
The authors proposed a key generation algorithm in [15] that takes an initial seed value of size 16 bits and generates a new key. This newly created key is only two bytes (16 bits) long. First, a 4 \(\times\) 4 matrix is generated during the key generation process. The initial key number is transformed into ASCII and eight DNA bases. The initial key nucleotide sequence is placed in the first and second rows of the matrix. The remaining rows of the matrix are filled with bio-DNA addition, and bio-DNA subtraction operations used to generate eight DNA nucleotides from the initial key. Based on bio-DNA addition, the first two values of the third row and the fourth row are generated. However, the key size of the proposed algorithm is too short, only 16 bits long; a brute force attack may easily guess the key. Secondly, the natural biological steps are ignored. The authors of [21] proposed two types of key generation for DNA encryption and decryption. The first type of key generation process is based on the EIGamal algorithm. The second type of key generation is based on DNA. The authors take random DNA sequences and generate public and private keys from the DNA codons. A random DNA sequence is generated using A, T, G, and C characters and stored in the database. However, the authors ignored the real biological steps for random key generation. Secondly, the key generation process takes a long time to encrypt and decrypt the message, as the EIGamal key generation process consists of complex calculations. The authors of [22] designed a cryptosystem using a Malay machine and DNA cryptography. They proposed a key generation algorithm based on user attributes, such as email address, username, and personal identification number, first converting each of these attributes to ASCII characters. Secondly, the attributes are merged and obtained as a single string. This string is converted to binary numbers of size 304 bits. The last key size of 256 bits is obtained with extra binary numbers removed from the binary string's right side. The authors completely ignored the biological steps for key generation. The authors of [23] used two dynamic encoding tables based on ASCII values. The first table is based on a 7-bit key taken from the dynamic encoding table. This table represents 96 ASCII characters as 7-bit binary sequences. The ASCII characters are randomly allocated to the 7-bit sequences, irrespective of their binary values. The second dynamic table is based on base 64 encoding rules. Each 6-bit sequence is assigned to a character from the base 64 encodings. However, character distribution is entirely random. The sender randomly chooses the 7-bit key from both tables and XORs the key with the 7-bit long plain text. Here the authors are missing the biological process, and the key size is short. The brute force attack may easily guess the real key after 27 combinations. The author improved \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Symbol** & **Description** & & \multicolumn{2}{c}{**Base Represented**} & \multicolumn{2}{c}{**Complement**} \\ \hline A & Adenine & A & & & & T \\ C & Cytosine & & C & & & G \\ G & Guanine & & & G & 1 & C \\ T & Thymine & & & T & & A \\ U & Uracil & & & U & & A \\ W & Weak & A & & T & & W \\ S & Strong & & C & G & & S \\ M & AMino & A & C & & 2 & K \\ K & Keto & & G & T & & M \\ R & Purine & A & G & & & Y \\ Y & Pyrinimide & & C & & T & & R \\ B & Not A (B comes after A) & & C & G & T & & V \\ D & Not C (D comes after C) & A & & G & T & 3 & H \\ H & Not G (H comes after G) & A & & C & T & & D \\ V & Not T (V comes after T and U) & A & C & G & & B \\ N & Any Nucleotide (not a gap) & A & C & G & T & 4 & N \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Complementary rules [20]. the key strength in [5], using the defi Hellman and genetic algorithm. This algorithm is computationally complex due to its complex operation. The authors proposed in [24] a long 1024-bit DNA-based key using DNA computing. They used the DNA XOR operation and DNA complementary rules.