WO2003005634A1

WO2003005634A1 - Information encryptation and decryptation method

Info

Publication number: WO2003005634A1
Application number: PCT/BR2002/000091
Authority: WO
Inventors: Sergio H. De Souza Motta
Original assignee: MM COMERCIAL DE PRODUTOS PROMOCIONAIS Ltda
Current assignee: MM COMERCIAL DE PRODUTOS PROMOCIONAIS Ltda
Priority date: 2001-07-04
Filing date: 2002-06-28
Publication date: 2003-01-16
Anticipated expiration: 2004-01-04
Also published as: BR0103525A

Abstract

The present invention concerns a process for the encryption and decryption of information presented in the form of characters, numbers, logos, images, etc., processed in a binary form. More specifically, it is related to a process of encryption of information by means of a multiplicative or comparative operation, a process of decryption of the encrypted information thus obtained, encrypted information and kit to decrypt encrypted information.

Description

Title of the Invention: "INFORMATION ENCRYPTATION AND DECRYPTATION METHOD"

DISCLOSURE OF THE INVENTION

The present invention concerns a process for the encryption and decryption of information presented in the form of characters, numbers, logos, images, etc., processed in a binary form. More specifically, it is related to a process of encryption of information by means of a multiplicative or comparative operation, a process of decryption of the encrypted information thus obtained, encrypted information and kit to decrypt encrypted information. BACKGROUND OF THE INVENTION

The need to improve and assure confidentiality of information has been receiving substantial attention, resulting in several studies and works on the part of the international community. It is well known that confidentiality can be achieved by the use of access passwords and/or keys that have the purpose not to allow non-authorized person to access or know the information. These needs are for commercial, industrial, computational or personal purposes.

Several applications as magnetic cards, credit cards, personal passwords, access passwords to restrict areas, passwords used in electronic terminal, require confidentiality of the information. In addition, lottery, games, advertisements, promotional and educative articles, promotional and contest systems, also represent applications where the confidentiality of the information is important.

Considering the information above, several forms of information protection and encryption are been developed using different methods. PRIOR ART

Several patent documents describe methods to retrieve the information in the form of images, intending to restrict non-authorized access to the information. The encryption and decryption of information are known in the prior art and can be exemplified by the patents US 5.790.703 and GB 2.289.973.

The patent US 5.790.703 presents a method of implementing digital watermarks using conjugated half tone screens, based on the introduction of difficult reproduction patterns in a document, or in the paper of a document, in order to attest is origin. This watermark can be partially or totally visible, allowing the attestation of the document origin to an interest person, without the use of an encrypted element for its complete understanding. This technique, nevertheless, requires an operation of reproduction of the document, for instance the transmittal of a fax message or making a reprographic copy, differently from the instant invention.

The document GB 2.289.973 describes a device and a method to generate encrypted images and a method of decryption. Such device consists of a set of two or more patterned masks, with at least one of them partially visible. The masks can be moved independently with relation to each other to oriented or pre-determined positions, superposing themselves, in such way as to show the desired image. The method to obtain such images is based in the juxtaposition and/or superposition of transparent masks, semitransparent masks, or apertured opaque masks, which contain the encrypted images. This document discloses that the images encrypted in each mask are obtained by a subtractive method of images, such that the reconstitution of the encrypted image occurs only by the concentration of noise when the masks are juxtaposed and/or superposed, resulting in low precision and eventual difficulty to perceive the information of the recovered image.

The present invention comprises a multiplicative or comparative method (also called bit inversion) of images, that is, more robust than the additive or subtractive methods, for the encryption of the information, in such way that the decryption process provides in at least one periodic or continuous region, retrieving the information in a clearer and more intelligible form, in comparison to object of the document GB 2.289.973.

DESCRIPTION OF THE INVENTION A typical embodiment of the invention is described as follows, imposing no limitation to its scope.

When two screens whose content are images with no visual meaning are superposed, following a pre-determined alignment, they reconstruct - with relation to an observer, be it person or equipment - an image containing the original information (as example, letters, numbers, figures, logos), which could not be recognized or decrypted without the superposition of at least two masks. In this reconstitution, at least one region of the reconstructed original information has the aspect of a periodic or continuous pattern (instead of a random aspect). The pattern of one of the screens is an arbitrary superficial random distribution, with no meaning, called a cipher element or mask. The other screen, independent of the information to be encrypted, has a two-dimensional distribution resulting from a multiplicative or comparative operation between the cipher element and the binary image to be encrypted. The encrypted information, therefore, is not a random distribution, although it has no discernible aspect to an observer.

In this context, the invention refers to four aspects:

- An encryption process: a series of steps that transform an image with intelligible visual information (one or more letters or numbers, an image, combinations of images and characters, etc.), in at least two images with no discernible aspect to an observer, resulting from a multiplicative or comparative operation. The result of this process is the encrypted information.

- A process to decrypted the encrypted information: a series of consecutive steps that reconstitute in a sufficiently discernible aspect the information previously encrypted, by the observation of two ore more superposed images, with no discernible aspect when observed individually. The resulted decrypted image is an image formed by two regions, one with a visual random pattern and the other with periodical images (dots, small images, etc.) or a continuous color or gray level distribution.

- Encrypted information: it is a non-discernible image obtained by the encryption process, resulting from the multiplicative or comparative information between the binary image to be encrypted and the cipher element or mask.

- A decryption kit: a set of at least two screens with no discernible image if observed separately, which, when superposed, reconstitute in a sufficient manner the information of the initial image to be encrypted (in that sense, protected), resulting in an image formed by two regions, one with a visual random pattern and other with periodical images (dots, small images, etc.) or a continuous color or gray level distribution. One of the advantages of the present invention is the visual definition of the recovered image obtained from the decryption process, containing two regions, one with a visual random pattern and other with periodical images (dots, small images, etc.) or a continuous color or gray level distribution. The contrast between the two regions allows a fast recognition of the recovered image.

Another advantage of the proposed method is the robustness of the encryption. The decryption of the encrypted information can be obtained only by the superposition of at least two masks of the decryption kit. The protected information cannot be obtained from a single mask. Considering that the encryption and decryption of the information are performed using a mathematical image processing, both processes, the encryption and decryption, can be implemented using computational calculations, in addition to or complementing the visual perception of the image. Other advantage of the invention is its easy implementation, considering it can be obtained using regular and inexpensive materials, like paper, plastic films, etc.

DETAILED DESCRIPTION OF THE INVENTION As considered in this text, the binary transformation of an image is its transformation into another image, formed by two colors, for instance black and white, red and green, or any other combination where there is substantial contrast between the two colors utilized. Considering the binary transformation of the image in gray levels in order to implement the mathematical image processing, once can to associate the color black to the gray level value 0 (zero) and to the color white to the gray level value 255. Also, it is possible to associate black and white to the values 0 and 1 , or -1 and 1. As is known to one skilled in the art, it is possible to transform any image into a binary image in order to give it a mathematical treatment. In the following text, even though the black and white colors are used to implement the encryption and decryption, the use of any combination of minimally contrasting colors to implement these operations are comprised in the scope of the invention

Within a first aspect of the invention , the process to encrypt the information comprises the following operations • Binary transformation of the image to be encrypted (the image represents the information).

• The multiplication or comparison between the binary image and the cipher element.

The multiplicative operation between images is known by one skilled in the art, and is described in technical literature, as in:

Optical Implementation of Image Encryption", Optical Engineering Vol. 35, no.

9, p. 2459-2463, September 1996.

Optical Implementation of Image Encryption Using the Phase Contrast Technique", Optical Pattern Recognition IX, David P. Casassent - Carnegie Mellon Univ., Tien-Hsin Chao - Jet Propulsion Lab, Editors - Proceedings of SPIE, volume 3386, p. 284-290, Orlando'98 SPIE's AeroSense Symposium, April 12-17, 1998. Optical image encryption based on input plane and Fourier Plane random encoding", Vol. 20, no.7, Optics Letters, April 1 , 1995.

"Optical implementation of image encryption using random phase mask and speckle free phase Fresnel holograms", Optical Pattern Recognition VIII, David P. Casassent - Carnegie Mellon Univ., Tien-Hsin Chao - Jet Propulsion Lab, Editors - Proceedings of SPIE, volume 3073, p. 389-396, Orlando'97 SPIE's AeroSense Symposium, April 22-23, 1997.

The herein referred comparative operation is also called bit inversion, and is performed as follows (supposing, for the sake of explanation, that there are black and white regions in the image to be encrypted): the image of the cipher element is superposed to the binary image, and where a particular region of the cipher element is over a black region of the binary image, the coincident dots in the cipher element are inverted, i.e., the black dots become white and the white dots become black. Where a particular region of the cipher element is over a white region of the binary image, the coincident dots of the cipher are preserved. The modified cipher element becomes the encrypted image.

The cipher element is a typical two-dimensional random distribution of numbers -1 and +1 (where -1 and +1 are related to the contrasting colors of the mentioned binary image). As an example, this distribution can be generated from the following equation:

where r varies between 0 and 4, x_n varies between 0 and 1 , transforming every value below 0.5 into -1 and every value below 0.5 into +1. This example of how to generate a random distribution using a non-linear equation is given in the article "Road to Chaos" from Kadanoff, L.P., published in Physics Today, December 1983, p. 46.

The process to generate the two-dimensional random distribution, as known to one skilled in the art, is not an essential aspect of the invention. Another aspect of the invention is the decryption process of the encrypted information using at least two masks.

The visual decryption of the information (previously encrypted by the process described hereinbefore) is obtained by the superposition and the alignment of the cipher element over the encrypted information. The decryption provides that the information previously encrypted is recovered as two regions, one with a two-dimensional random distribution or a visual noise, and the other with a periodic or continuous color or gray level region.

The decryptation requires the superposition of two screens having, respectively, the image of the cipher element and the image of the encrypted information. For this operation, it is necessary that the mask between the observer and the inferior mask has substantially translucent or minimally transparent regions, allowing the visualization of the two combined masks. In this manner, the inferior screen has, as an example, black and white regions, and the superior screen has black and transparent or translucent regions, or regions with perforations or other characteristic allowing the transfer of light.

Another aspect of the invention is the image of the encrypted information, which is obtained by the multiplication of the binary image

(obtained from the initial binary operation) with the cipher element, or by the comparison between the cipher element with the binary image followed by the bit inversion.

Another aspect of the invention is a kit comprised of at least two screens or masks which, when superposed, reconstitute in a sufficiently discernible way the information of the original encrypted image, characterized by the fact that the superposition of the two masks reconstitute an image composed of the two substantially contrasting regions, one with a two- dimensional random distribution or a visual noise, and the other with a periodic or continuous region.

The images of the cipher element (a two-dimensional random distribution) and encrypted image (obtained from the multiplication of the binary image with the cipher element, or by the comparison between the cipher element with the binary image followed by the bit inversion) may be generated over different surfaces, planar or spherical, keeping in mind that the aligned superposition is what reconstitutes the original information. In this manner, any surface that allows or supports the generation of an image can be utilized. Practically, all surfaces allowing or supporting the generation of an image can be utilized, like paper, plastic, glasses, metals, etc. These materials can be used for different applications in documents, bank documents, badges, cards, promotional tickets, walls, televisions or video screens, computer monitors, liquid crystal televisions, or any other physical or electronic support that allows its visualization and/or reconstitution.

The images of the cipher element and encrypted information can be formed by conjugated subcomponents, i.e., the visual aspect of each mask (cipher element or encrypted information) can be formed by the superposition, juxtaposition, or any type of combination of two or more images (added, subtracted, multiplied, compared, etc.).

There is no limitation in the use of two or more colors in the images of the cipher element and encrypted image, provided that no substantial restriction will result in the sufficient recovery of the encrypted information.

Dots, lines, stars, or any kind of images forming a two-dimensional random distribution can be used in the black region of the encrypted element. The images of the cipher element and encrypted information can be associated with any materials. The manufacture processes of these materials do not limit the invention, so that different industrial processes of impression, photolithography, flexography, perforations are adequate to the invention.

The necessary orientation allowing the alignment of the screens or substrates containing the images of cipher element and encrypted image can be obtained by any known manner. As an example, alignment marks, pin, guides, marks, arrows, lines, using physical or electronically processes, etc. DETAILED DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION

One particular embodiment of the invention is described below, showing the typical steps of the encryption and decryption processes of the invention. This example does not impose any limitation to the scope of the invention, defined by the claims presented later on. I- The information to be encrypted is chosen (character, number, logo, image, etc.), as an example, the image of the number 2, as shown in Figure 1. The image of Figure 1 is formed by the matrix AMN of MxN elements. The black color represents the gray level 0 (zero), and the white color the gray level 255.

II- Based on the binary distribution of Figure 1 , an MxN matrix B_MN is generated with the elements formed by the numbers -1 and 1 (+1). The number

-1 is associated to the region in black color (gray level 0), and the number 1 is associated to the region in white color (gray level 255), as shown in Figure 2. The matrix B N is called the binary information of the image to be encrypted. As the number of elements of the matrix B_MN is increased, a better precision is obtained in the later process of decryption.

III- In the sequence, each element of the matrix BMN is multiplied by the respective element of a new MxN matrix C-MN, called by cipher element, which is formed by a binary two-dimensional random distribution of -1 and 1 (generated by numerical methods in computers or other methods). The MxN matrix DMN resulted from this multiplicative operation contain the encrypted information. The operator "•x" in Figure 3 indicates the element by element multiplication to calculate the matrix DMN, i.e., DMN=BMN»XC_MN => d_mn=b_mn.c_mn, where d_mn, bmn.and c_mn are the elements of the matrix DMN, B_MN and CMN, and "m" and "n" are the indices of the matrix elements.

As mentioned before, the matrix CMN of the cipher element can be obtained using well-known mathematical functions used to generate random distributions, or by using non-linear equations with a chaotic behavior, generating a white noise uniformly distributed, i.e., a random distribution. The advantage of using chaotic equations is the easy generation and reproduction of the random distribution of the cipher element from the previous knowledge of an initial numeric value, the bifurcation parameter of the equation, and the precision of the numeric calculations previously saved. IV- Using the matrix D and CMN, one obtains the images of the encrypted information and cipher element, as shown in Figure 4. The cipher element is formed by a two-dimensional random pattern that can be printed over a physical surface. In the region associated to the number -1 , the light is blocked by the black color, and the region associated to the number 1 is transparent, allowing the passage of light. The gray regions in Figure 4 show where the cipher element should be totally or partially transparent. The image of the result encryption has the aspect of a two-dimensional random distribution, but in reality, this distribution is a two-dimensional pseudo-random distribution, i.e., a distribution extremely noisy with the information of the initial image in an intelligible form, impossible to be obtained visually, mathematically or numerically without the knowledge of the cipher element. This impossibility is described in the technical reference "Two-Dimensional Imaging", Ronald N. Bracewell, Prentice Hall Signal Processing Series, p.570, ISBN 0-13-062621 -X. The images of Figure 5 show an example of encryption for the image of the number "2" (Figure 5a), with the corresponding images of the cipher element (Figure 5b), of the encrypted information (Figure 5c), of and the decrypted information (Figure 5d). The decryption of the information is performed when the cipher element is superposed in an alignment form over the image of the encrypted information. Each pixel in the images of the cipher element and encrypted information represented by the black color, as shown in Figure 4, can also be represented by small arbitrary binary images (stars, dots, squares, lines, small images, etc.), as shown in Figure 5. The gray regions in Figure 5b show where the cipher element should be totally or partially transparent.

The use of small arbitrary binary images helps in the visual alignment of the cipher element and in the perception of the decrypted information. In Figure 5d, the region with periodic distribution corresponds to regions with the gray level value 0, the black color of Figure 5a, and the region with random distribution correspondes to the gray level value 255, the white color of figure 5b. The information of Figure 5d is visually intelligible without the aid of video or photographic cameras, with good definition.

Automatic identification systems can also be implemented in the decryption process of this invention. In these systems, the image of the cipher element can be read using video or photographic cameras, scanners, digitalizers or any other optoelectronic processes of image capture, or the combination of these methods. After the digitalization of the image of the cipher element, such image can be aligned with the image of the encrypted information previously digitalized and stored in the memory of the identification system using numerical methods.

The binary encryption/decryption process of the invention (also called module 2 operation) does not require the use of coherent and/or polarized light, although such resources can be employed.

Also, for the encryption/decryption processes of the invention, it is not necessary the use of lenses, prisms, mirrors or any other process of reflection, refraction or diffraction of the light, although one can use these devices or processes for the encryption/decryption process.

This encryption process of the invention is robust, because the distribution D_mn is preferentially obtained by the mathematical operation of multiplication D_mn=Bmn.C_mn described in item 3. Considering that C_mn has a random distribution, that is, a white noise uniformly distributed, the information of B_mn, encrypted in D_mn, can be recovered only with the previous knowledge of the information of C_mn. In this manner, if the information of C_mn is lost or not known, it is not possible to recover e the information B_mn encrypted in Dmn- In this method, the distribution with the encrypted information is correlated to the distribution of the cipher element. Although this invention was described by means of a particular embodiment, other alternatives will be readily apparent to one skilled in the art, without departing from the scope of the subjects of the invention. The attached claims aims at protecting such modifications and changes within the scope of the invention, as well as its equivalents.

Claims

1. An information encryption process, characterized by the fact that it comprises the steps of (1) binary transformation of the image containing the information, and (2) the operation of multiplication or comparison between the binary image and a specific cipher element, the cipher element being a two- dimensional random distribution, and the resulting encrypted information provided with the visual aspect of a two-dimensional random distribution.

2. A process according to claim 1, characterized by the fact that said multiplication or comparison operation is performed with the use of computational resources.

3. A process according to claim 1, characterized by the fact that the result of the binary transformation comprises only a gray color distribution.

4. A process according to anyone of claims 1 to 3, characterized by the fact that , in the cipher element image or in the encrypted information image, the lighter color regions are replaced by totally or partially transparent regions.

5. A process according to claim 1 characterized by the fact that the images of said cipher element or said encrypted information may be printed or materialized as images, and that they may be in superposition.

6. A process of decryption of encrypted information according any one of the claims 1 to 5, characterized by the fact that it comprises the superposition and alignment of the cipher element and the encrypted information, obtaining the reconstitution of the image of the initially non- encrypted information, in a substantially intelligible form, comprising two contrasting regions, namely (a) one region of random distribution of images, and (b) another region of a periodic distribution of dots or small images, or of continuous color.

7. A kit to decrypt encrypted information, characterized by the fact that it comprises at least two images that can be superposed and aligned, such images corresponding to (a) a cipher element and (b) to the encrypted information according any one of the claims 1 to 5.

8. A kit according to claim 7 characterized by the fact that at least one of the images is printed on paper and the other on a transparent substrate.

9. Encrypted information characterized by the fact that it is obtained by an encryption process according to any one of claims 1 to 5.