Color Image Integrity Verification Using Shamir’s Secret Sharing Scheme

A Novel watermarking technique to verify the integrity of the lossless color image (BMP image) using Shamir’s (k,n)-threshold Secret-Sharing Scheme via the use of Portable Network Graphics (PNG) image is proposed. An authentication signal is generated for each block of color image which is transformed into several shares using Shamir’s secret sharing scheme. The coefficients of the polynomial used by the Shamir’s method are used as carriers to carry given authentication signals. The partial shares are embedded into an alpha channel plane. The alpha channel plane is then combined with the original lossless BMP color image to form a PNG image. Undesired white noise created in the resulting transparent stego-image is removed by carefully mapping the computed share values into a range of alpha channel values near their maximum value of 255 in the embedding process. In the process of verifying the integrity of the image the authentication signals are computed from the current block which is then compared with the extracted shares from the alpha channel plane for the corresponding block. If the authentication signals doesn’t match then that block is marked as tampered. The proposed image authentication method possesses the merits of losslessness during image verification, high sensitivity to image alterations, good tampering localization capability, and very low false acceptance and rejection ratios. Experimental results proving the effectiveness of the proposed methods are also included.