Enhanced Least Significant Bit Scheme Robust against Chi-Squared Attack

Among the steganographic techniques and particularly in conventional least significant bit (LSB) insertion method, there is a challenging issue and that is how to embed desired secret bits in a cover medium (a typical 8-bit gray-scale image) in a way not to be seen by human vision system as well as the fact that it is expected not to be attacked by some attacks like chi-squared attack, etc. The point is how to maintain robustness and the highest acceptable imperceptibility. Although by using more pixels for estimating each target pixel’s capacity, bigger imperceptibility is achieved, there is another problem that the higher probability of being attacked by Chi-squared index is expected as the desired amount of secret bits increases. This paper proposes a method that utilizes more surrounding pixels (unlike BPCS, PVD and MBNS methods which use 3 or 4 immediate neighbors of each pixel). In this regard, for each certain target pixel, a more precise number of bits known as capacity, is found to be filled by respective secret bits. Finally, it is proved that the method is robust against Chi-squared attack. The new method is called MSP and it stands for more surrounding pixels.