METHOD FOR STEGANOGRAPHYING A DIGITAL IMAGE USING A GRAPHIC DIGITAL LABEL AND METHOD FOR DECRYPTING A STEGANOGRAPHIED IMAGE

摘要

FIELD: information security.;SUBSTANCE: invention relates to methods and systems for steganographying a digital image using a graphic digital label and decrypting steganographied digital images. In the method a) at least one input image is obtained; b) the hash sum of said input image is formed; c) the resulting hash sum is encrypted; d) a checksum is created based on the encrypted hash sum of the image; e) a data tuple consisting of the resulting hash sum and checksum is formed; f) based on the resulting tuple, a DL is formed in the form of a digital image containing the data in a graphic representation; g) the matrix of brightness values of pixels of the graphic DL is formed by executing the following stages: - converting the DL image pixel-by-pixel from RGB to the HSV colour space, followed by building the matrix of brightness values of pixels in the DL image (Im), - in the matrix of brightness values of pixels in the DL image (Im), rounding the values falling within the range from 0 to 1 upward or downward; h) the matrix of complex numbers from the brightness values of pixels of the input digital image is formed by executing the following stages: - converting the DL image pixel-by-pixel from RGB to the HSV colour space, followed by building the matrix of brightness values of pixels in the DL image (Ip) and forming the matrix of hue (Hp) and saturation (Sp) values of the pixels of the image in the HSV colour space; - forming a tuple K(Ip) from the brightness values of pixels by line-by-line conversion from the resulting matrix of brightness values of pixels (Ip); - forming a tuple of complex numbers K(If) by applying a direct discrete fast Fourier transform (DFFT) to the brightness tuple; - forming a matrix of complex numbers (If) from the tuple of complex numbers K(If) of the same dimension as the matrix of brightness values of pixels (Ip) obtained in step 1); i) an intermediate steganogram matrix (Io) is created by adding the matrices obtained at stages h) and g), wherein the matrix of brightness values of pixels of the graphic DL (Im) and the matrix of complex numbers from the brightness values of pixels of the input digital image (If) are added; j) from the intermediate steganogram matrix (Io) obtained at stage i), the matrix of brightnesses of pixels of the steganogram (I*) is formed by means of a reverse discrete fast Fourier transform (DFFT)); k) a matrix is formed, containing all three values (Hp, Sp, I*) of the HSV colour space, describing the steganographic digital image wherein the values of cells from the matrix of brightnesses of pixels of the steganogram (I*) obtained at stage j) are combined with the values of the matrices of hues (Hp) and saturation values (Sp) of the input digital image obtained at stage h); l) based on the matrix obtained at stage k), the steganographic digital image is reproduced by transferring each cell of said matrix (Hp, Sp, I*) from the HSV colour space into the RGB colour space.;EFFECT: ensured protection of images due to the introduction of digital labels.;25 cl, 7 dwg