Patent RU-2761417-C1 (RU)
Title: Method for steganographying a digital image using a graphic digital label and method for decrypting a steganographied image
Inventor: Kramarenko Sergej Mikhajlovich
IPC: G06F17/00
Filed: 2020-11-05
Granted: 2021-12-08
Abstract: 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 (I m ), - in the matrix of brightness values of pixels in the DL image (I m ), 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 (I p ) and forming the matrix of hue (H p ) and saturation (S p ) values of the pixels of the image in the HSV colour space; - forming a tuple K(I p ) from the brightness values of pixels by line-by-line conversion from the resulting matrix of brightness values of pixels (I p );  - forming a tuple of complex numbers K(I f ) by applying a direct discrete fast Fourier transform (DFFT) to the brightness tuple; - forming a matrix of complex numbers (I f ) from the tuple of complex numbers K(I f ) of the same dimension as the matrix of brightness values of pixels (I p ) obtained in step 1); i) an intermediate steganogram matrix (I o ) is created by adding the matrices obtained at stages h) and g), wherein the matrix of brightness values of pixels of the graphic DL (I m ) and the matrix of complex numbers from the brightness values of pixels of the input digital image (I f ) are added; j) from the intermediate steganogram matrix (I o ) 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 (H p , S p , 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 (H p ) and saturation values (S p ) 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 (H p , S p , 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