A novel 3-D image encryption algorithm based on SHA-256 and chaos theory

The security of 3-D images is an important research problem that has to be resolved. Due to the more complex structure of 3-D images, the encryption of these images is quite different from 1-D and 2-D images. A three-stage novel image encryption technique based on chaotic maps is presented in this paper in which a 3-D image is firstly converted to a similar image format as that of 2-D images before encryption. The initial conditions of the chaotic system are generated by using the SHA-256 function on the coordinate matrix of the plaintext. Initially, a logistic map is utilized to scramble and add random points to the coordinate values of vertices of a 3-D image. The coordinate values are then confused and diffused in the second stage by using three sequences generated through the logistic-dynamic coupled logistic map lattice (LDCML) model. This stage also involves splitting of floating point data into integer and fractional parts. The integer part is diffused whereas the fractional part is scrambled during this process. In the third stage, the confusion is performed by using a tent map among the coordinate points. This process enhances the robustness, integrity, and confidentiality of 3-D images and ensures protection against unauthorized access. The proposed encryption procedure achieves values of correlation close to zero along x,y,z- directions, NPCR of 100%, UACI of 33.37%, and entropy value of 7.9993 which demonstrates its robust security. The time analysis shows that our technique improves efficiency and lowers computational costs by processing data in a lesser time. The security and statistical analysis concludes that the proposed encryption algorithm can withstand various conventional attacks.