Visually meaningful image encryption algorithm based on digital signature

Traditional image encryption algorithms transform a plain image into a noise-like image. To lower the chances for the encrypted image being detected by the attacker during the image transmission, a visually meaningful image encryption scheme is suggested to hide the encrypted image using another carrier image. This paper proposes a visually meaningful encrypted image algorithm that hides a secret image and a digital signature which provides authenticity and confidentiality. The recovered digital signature is used for the purpose of identity authentication while the secret image is encrypted to protect its confidentiality. Least Significant Bit (LSB) method to embed signature on the encrypted image and Lifting Wavelet Transform (LWT) to generate a visually meaningful encrypted image are designed. The proposed algorithm has a keyspace of 139.5-bit, a Normalized Correlation (NC) value of 0.9998 which is closer to 1 and a Peak Signal to Noise Ratio (PSNR) with a value greater than 50 ​dB. Different analyses are also performed on the proposed algorithm using different images. The experimental results show that the proposed scheme is with high key sensitivity and strong robustness against pepper and salt attack and cropping attack. Moreover, the histogram analysis shows that the original carrier image and the final visual image are very similar.