Partial-privacy image encryption algorithm based on time-varying delayed exponentially controlled chaotic system

To enhance privacy protection for specific regions within an image while preserving its overall visual integrity, this paper presents a visual encryption algorithm targeting partial privacy-sensitive areas. Initially, an improved time-varying delayed exponentially controlled chaotic system (1-TDEC) is proposed. It utilizes the current precision value to modify the system input in a time-varying manner, effectively alleviating the dynamic degradation, and making it more suitable for image encryption algorithm designs. Subsequently, the Mask-RCNN instance segmentation model is incorporated to capture the pixel coordinates of different contents in the image, allowing for access to specific area information as required. Furthermore, this encryption algorithm employs a comprehensive permutation process along with parallel bit-shift coupling, effectively transforming the image target areas into visually meaningless forms. It also separately encrypts each bit plane, enabling the encryptor to implement different decryption effects by assigning key streams with different lengths. Finally, the comprehensive performance analysis results highlight that the designed algorithm achieves a maximum information entropy value of 7.9998 in encrypted images. Moreover, its resistance to differential attacks (as measured by NPCR and UACI) and pixel correlation are infinitely close to the ideal state, significantly underscoring its security and effectiveness.