With the fast development of Internet technology, digital images have become an essential way of information storage and transmission. In medicine, medical digital images are rich in sources and diverse in forms, has become an important auxiliary tool for the prevention, diagnosis and treatment of diseases. which can help doctors to understand the treatment and diagnosis of diseases, so as to provide patients with more excellent and advanced treatment methods. Medical images include physiological and pathological information about the human body, and they often also involve the privacy of patients, and there is a certain need for confidentiality. However, malice hackers tend to seek to steal medical images through illegal tactics, selling the information or engaging in privacy extortion for financial gain. Therefore, in order to avoid information leakage and privacy exposure, effective protection measures should be built into medical images so as to ward off criminal elements' malicious attacks and extortion.
Currently, the most common methods to protect the content of medical images are medical image watermarking, medical image steganography and medical image encryption, In this, medical image cryptography is the most powerful means of securing the images because it can convert the original medical image into an unreadable one by means of a key. It has many medical image encryption methods to improve the security of the image. And in improving the security of medical image cryptography it mainly depends on these three phases of the encryption process which are key, scrambling and diffusion phases. In the case of key, the key is mainly created by introducing chaotic mapping to improve the security of the key. Whereas in the case of disarray, it mainly changes the pixel position without changing the pixel value, the diffusion phase mainly changes the pixel value.
In recent years, researchers have proposed many medical image encryption techniques, for example, For example, Ammar[1] proposed an algorithm is based on combining a seven-dimensional hyperchaotic regime with Pascal's matrix, but it has a simpler encryption process. Li et al[2] proposed a medical image cryptography algorithm based on hash algorithm, DNA encoding and four-dimensional hyper chaotic system, but its key is relatively easy to be cracked. Xiong et al[3] proposed a medical image cryptography algorithm based on improved chaotic system, block rotation and DNA computation to design a fully chaotic, strong plaintext management, but the algorithm is simpler in the process of DNA operations. Gao et al[4] proposed a hybrid multi-image encryption algorithm that can encrypt different types and sizes at the same time, and DNA operations are also used in the process. But the encryption time of this algorithm is too long. Yasmine et al[5] proposed a grey scale image encryption model based on dynamic DNA coding, hash function, and Arnold transform, but the complexity of its algorithm is too high.
After learning from the above experiences and based on the existing work and progress, in order to improve the safety of algorithm and to decrypt it correctly even if it is attacked by external attack during transmission, this paper proposes a medical image encryption algorithm based on helical transform and dynamic DNA, and the main innovations of this paper are as follows:
1. Spiral transformation is based on chunking, which can choose the appropriate sub-chunk size according to the size of medical images, thus enhancing the encryption effect and accelerating the encryption efficiency;
2. In the diffusion process, eight DNA coding rules, three DNA arithmetic rules and one random DNA decoding rule are introduced, which can complete the full diffusion operation on the scrambled image.
3. The encrypted medical image has better performance against clip attack and can protect the central region from loss;
After experimental simulation and performance evaluation analysis, it is evident that the algorithm exhibits a high level of comprehensiveness compared to current industry advanced encryption algorithms in the industry. The encryption process is straightforward and suitable for practical scenarios.
The rest is organized as shown below. Section II presents the theoretical theory of the algorithm. Section III describes in detail the encryption algorithm's structure and steps. Section IV shows the experimental emulation outcomes. Section V is the specific performance analysis. Section VI summarizes the work and expresses the future outlook.