Information security is one of the most important fields that has been gaining more attention for data protection, privacy preservation and data leakage prevention. The process of securing information systems includes monitoring and analyzing all data flows and behaviors of different components that comprise the system, such as people that interact with the system; hardware, such as network infrastructure, routers and domain name servers; and software configurations and keys. It is a necessity to ensure that the system is fully functioning while protecting its components from known and unknown threats. The basic requirement for any security system is to achieve the following requirements: integrity, confidentiality and availability. Other requirements also include accountability and authentication. Encryption, also known as cryptography, is the most widely used approach to achieve confidentiality and verify integrity. It is also the main way to secure governments, social data and personal transactions, since all of these entities require a great amount of protection against known/unknown attacks and threats. In this sense, cryptography is the most fundamental building block in the design of secure information systems. As a result, it has attracted the main interest of many researchers, allowing thousands of competing research articles to offer new ways for fast and robust encryption.

Cryptography is divided into two broad categories: symmetric cryptography and asymmetric cryptography. Symmetric cryptography uses a single key for both encryption and decryption, also known as single-key cryptography. Some examples are the Advanced Encryption Standard (AES), Data Encryption Standard (DES), 3DES and Rivest Cipher 4 (RC4). Asymmetric cryptography, also known as public-key cryptography, uses one key for encryption and another key for decryption. Some examples of public key cryptography are the Rivest–Shamir–Adleman (RSA) algorithm, Elliptic Curve Cryptography (ECC) and the Diffie–Hellman key agreement protocol.

Because of the wide spread of wireless networks, LANs, Bluetooth, and other forms of communication media, digital images should be protected to maintain privacy and copyrights. Images may be vulnerable to different types of attacks during transmission or exchange between authenticated users. Some common attacks related to networks are network denial, masquerading and eavesdropping. For any communication medium to be trusted between parties, it should satisfy reliability, anonymity, confidentiality, integrity and availability. When exchanging digital images, common ways for securing these images are cryptography and steganography. Cryptography not only guarantees confidentiality, but it can also address other issues such as data integrity, authentication and non-repudiation. With cryptography, information can be sent securely, and only the authenticated receiver can retrieve this information, thus avoiding the compromising or leakage of private data.

The RGB model is a widely used model for representing and storing digital color images. In this model, the image is represented by three independent channels. Each channel is a 2D matrix. The first matrix represents the red color, the second matrix represents the green color and the third matrix represents the blue color. The three matrices are of the same width and height. Each pixel in the color image is represented by three values that are the three corresponding values on the three matrices. Each value can range from 0 to 255. In this way, the RGB model can represent more than 16 million distinct colors. Many recent scientific papers have shown that combining DNA cryptography and chaotic sequences leads to very efficient and promising results with respect to nonlinearity, randomness and resistance to common attacks. Arthi et al. ^[1] presented an encryption technique based on 4D Lorenz hyper-chaos and DNA encoding. First, an integer wavelet transform IWT is applied to produce approximation and detail bands of the input image. Then, the LL band is permuted using chaotic sequences, and then they are encoded using DNA. Finally, an operation called DNA-XOR is performed to produce the encrypted image. Paul ^[2] presented a color image encryption technique that uses a 2D hyperchaotic map to scramble the initial image and then uses a logistic-tent map to produce a cover image. Then, SHA-2 is applied to this cover image to produce a mask image, and the two images are encoded using DNA, followed by many diffusions to produce cipher image.

2. DNA Cryptography