FPGA realization of an image encryption system using the DCSK-CDMA technique

This paper describes a four-wing chaotic oscillator-based DCSK-CDMA modulation technique for image encryption and decryption. The system consists of a transmission module for the encrypted and modulated color matrices, and a reception module for the decrypted and demodulated original data. Among our main contributions is the integration for the first time in the state of the art of DCSK chaotic modulation techniques with the CDMA communication scheme, as well as the implementation of our DCSK and CDMA algorithms in VHDL language for Xilinx FPGA cards. The DCSK-CDMA technique enables demodulation and decryption without any loss in the original data. Other contributions arising from this investigation are the encryption process implemented using DCSK-CDMA techniques based on a four-wing chaotic oscillator and the realization on the FPGA of a chaos-based communications system for the secure transmission of images of grayscale and RGB formats using DCSK-CDMA techniques. The system architecture in this work was designed using fixed-point binary arithmetic, with the application of the 4th order Runge–Kutta numerical method for the four-wing chaotic oscillator. The analysis of the correlation coefficients between the original and encrypted information indicates the values of $5.367\times 10^{-4}$ and $-2.205\times 10^{-7}$ for grayscale and RGB images, respectively, with a full recovery of the original information. The results of simulations in MATLAB/Simulink coincide with the implementation of the complete system in VHDL on the Xilinx Artix-7 AC701 board.