A Novel Chaotic Image Encryption Algorithm based on Coordinate Descent and SHA-256

Since each encryption necessitates the transmission of the key, chaotic image encryption methods with key and plaintext association have emerged in recent years. These algorithms are essentially one-time pad at a time. Nevertheless, some current systems are unable to map the seed key to the chaotic system's initial value in a unique way, which reduces the encryption system's key space. Furthermore, some techniques defy the one-time pad strategy by encrypting the same image with the same key. These issues are resolved in this paper in two ways. On the one hand, SHA-256 is used to calculate a hash value after randomly inserting pixels into a plain image. Even if the same image is encrypted, several seed keys can be obtained. However, to achieve the one-to-one connection between the seed key and the encrypted key stream, the Sequential Expansion Algorithm (SEA) and Feedback Iterative Piece-Wise Linear Chaotic Mapping (FI-PWLCM) are suggested. Random and seed key sensitive sequences can be produced rapidly via SEA. FI-PWLCM uses feedback iteration with additional control settings to achieve one-to-one correspondence with the seed key. The mapping can generate more intricate chaotic sequences in addition to having the speed of PWLCM. Additionally, in order to strengthen cryptosystems' resistance to statistical attacks, this study suggests the Segmented Coordinate Descent (SCD) technique for histogram statistical optimization of images. The algorithm can withstand brute force attacks, statistical attacks, chosen-plaintext (chosen-ciphertext) attacks, and more, according to experiments and security research. It performs best in the statistical qualities of entropy and histogram when compared to the majority of existing algorithms