CN108171642A - The asymmetrical optical Information Hiding Techniques of view-based access control model cryptography - Google Patents

Abstract

The invention discloses a kind of asymmetrical optical Information Hiding Techniques of view-based access control model cryptography.View-based access control model cryptography encryption technology, by phase distribution information come the subgraph of concealed encrypted generation, and the phase type object of the method making hiding information using binary optical, finally the further hidden information of phase object is covered using the method for amplitude image.Visual cryptography subgraph is extracted using optical diffraction method, and is coupled by optical element and realizes that subgraph is superimposed to obtain hum pattern, last human visual system directly extracts hiding information.The present invention is based on visual cryptography encryptions, are distributed hiding information using the phase information of phase object first, reuse twice hidden of the amplitude image obscure realization to phase object, have high concealment and safety.Optics, the information extracting method of asymmetric are simple, quick simultaneously, high practicability.It is applicable to concealment, safety, the high Information hiding field of simple operation requirement.

Description

Asymmetric Optical Information Hiding Technology Based on Visual Cryptography

technical field

The invention relates to an optically realized information hiding technology, in particular to an asymmetric information hiding technology based on visual cryptography, using phase objects to hide information and amplitude images to cover up phase information, and extracting information easily through optical diffraction.

Background technique

The ability of the human visual system to identify correlations and the ability to encrypt image graphics with random grids has laid a solid foundation for using images to encrypt information. Thereafter, Moni.Naor and Adi.Shamir proposed visual cryptography in 1994, and demonstrated the feasibility and security of this method from a mathematical point of view, see (Eurocrypt 199(1):1-12, 1994). Visual cryptography encodes information-carrying images into multiple mosaic pseudo-random images by means of pixel expansion. When decrypting, only a sufficient number of images need to be aligned and superimposed, and the image information can be decrypted by human eyes. The visual cryptography scheme has good encryption security performance and simple decryption operation, and has received extensive attention since it was proposed. However, since the key is an amplitude image, its concealment defect has not been well resolved.

The reason why the human eye and optical imaging system can observe images and detect information is that the light intensity distribution can be perceived by the system, and the images formed by the light intensity distribution are all amplitude images, so the amplitude images are directly visible. The phase information is invisible to the light intensity, and the information of the phase object cannot be directly detected by the naked eye and the intensity detection device, which has a high degree of concealment. This characteristic provides great convenience for information hiding. The development of phase recovery algorithms has greatly promoted the application of phase objects. The G-S algorithm is the first to calculate the phase information of an object. Through multiple iterative calculations, the phase distribution of the amplitude image can be obtained, and the original amplitude image can be restored through diffraction. See (Opt.35(2):237-246, 1972). In addition, the error reduction algorithm and mixed input-output algorithm proposed by J.R.Feinup et al. provide convenience for the application of the phase recovery algorithm in different scenarios. The efficiency of the phase recovery calculation is continuously improved, and its application is also extended to more fields. See (Appl. Opt. 21(15):2758-2769, 1982).

The traditional information hiding technology mainly adopts the method of embedding information image into the host image, embedding information into the host image and using the information mask of the host image to hide the information to achieve the purpose. Such information hiding is mainly realized by digital methods. When extracting information, corresponding to the hiding process, the reverse operation can be completed. Overall, the hiding and extraction process is symmetrical, which increases the complexity of the application to a certain extent. sex. Image information is the main product of optical effects, and the advantages of parallel processing and intuitive effects of optics have not been fully utilized in traditional information hiding. More importantly, the advantage of high concealment of phase information is rarely used in practice.

Contents of the invention

The purpose of the present invention is to fully combine high-security, easy-to-operate visual cryptography and highly concealed phase object correlation technology, and use optical correlation characteristics to obtain an optical information hiding method with good concealment performance and simple and fast information extraction. The method proposed by the invention mainly utilizes the characteristic that the phase information carried by the phase object is invisible in intensity to realize information hiding, and uses the amplitude image to cover the phase object to further improve the concealment of information. In addition, the hidden pre-encryption operation in the proposed method fully guarantees the security.

The information hiding method proposed by the present invention is realized by combining visual cryptography and diffractive optics. The information that needs to be hidden is first encrypted by visual cryptography to improve information security; then the phase information of the ciphertext is calculated using the phase recovery algorithm, and processed into a phase object to achieve the basic purpose of hiding; finally, the amplitude image is overlaid on the information-carrying On the phase object, the concealment of information is further improved to achieve the purpose of hiding information with high security. Through the information hiding scheme proposed by Ben Daming, the phase object produced by preliminary hiding is a transparent glass plate with no difference in appearance from ordinary quartz glass, and the existence of information cannot be detected by human eyes and intensity detection. After the amplitude image is covered again, the concealment of the information is further improved due to the prominent performance of the light intensity information on the phase object. In information extraction, as long as the plane light wave is used to directly irradiate the phase object covering the amplitude image, and then the optical element is used to couple the image generated by diffraction, the hidden information can be directly extracted through the human eye.

The present invention is based on visual cryptography technology, combined with phase recovery algorithm and binary optical element technology, and can be realized through the following technical measures:

(1) Encrypt the information (X) to be hidden according to the visual cryptography method, and encode it into N encrypted sub-images (A1, A2, ..., An) through pixel expansion. When the K sub-images are superimposed, they can be passed Human eyes get decrypted information (X)

(2) Through the phase recovery algorithm, calculate the phase distribution corresponding to each sub-image (A1, A2, ..., An), and obtain the corresponding pure phase distribution image (B1, B2, ..., Bn)

(3) The phase information in all the phase distribution diagrams (B1, B2, ..., Bn) is uniformly stepped, and its phase value is converted into the corresponding depth value on the binary diffractive optical element to obtain a stepped phase distribution graph(C1,C2,...,Cn)

(4) Use the binary diffractive optical element processing method, according to the depth information of the stepped phase distribution diagram (C1, C2, ..., Cn), design and manufacture the mask plate, and then use photolithography according to the mask plate Technology to process stepped binary diffractive optical elements (D1, D2,..., Dn)

(5) Print the amplitude images (E1, E2, ..., En) onto the transparent sheet, and cover the printed transparent sheet on the binary diffractive optical element (D1, D2, ..., Dn) by pasting. Above, the objects (F1, F2, .

(6) Design and build an optical path for extracting information according to the number of objects with hidden information. The plane light waves are respectively irradiated on the objects with hidden information (F1, F2, ..., Fn) after beam expansion, and then use Fourier The lens images the diffracted light into the near field, and the diffraction images (G1, G2, ..., Gn) corresponding to the amplitude sub-images (A1, A2, ..., An) will be obtained on the back focal plane of the Fourier lens )

(7) Use an optical element to couple the diffracted light beam to realize the superimposition effect on the sub-images (G1, G2, ..., Gn) restored by diffraction, and after adjusting the alignment of the coupling element, an image carrying information (X) is obtained, Finally, the information (X) can be extracted by human eyes.

In the actual operation process, the Fourier lens mentioned in step (6) can be selected not to be used, and the diffracted light is directly imaged to the far field, and the information can also be extracted after coupling the light beam through the optical element.

Compared with the existing information hiding technology, the present invention has the following advantages:

(1) The present invention uses phase objects and phase information to hide original information. The invisibility of the intensity of phase information provides extremely high concealment, and the concealment and security of information hiding are greatly improved.

(2) The present invention uses the method of combining the amplitude image and the phase object to realize hiding twice, and then uses the amplitude information to hide the phase information after the phase object hides the information, which further improves the security of information hiding, and the form of the amplitude image makes the method It is more convenient in application.

(3) In the way of hiding information in the present invention, when hiding information, the information is first encrypted instead of being hidden directly, which further improves the security of hiding, reduces the possibility of information leakage, and makes the application more secure

(4) The present invention is an asymmetric information hiding method, and the information hiding process is complicated, which ensures high security of hiding; while the information extraction process is very simple and fast, and is more convenient in practical application.

(5) The present invention makes full use of related processes and phenomena of optical processing, and the process of extracting information is intuitive. At the same time, the combination of various optical technologies further enhances the safety performance.

The asymmetric optical information hiding technology based on visual cryptography disclosed by the present invention is applicable to the field of information hiding that requires high security performance and the information extraction method is simple and quick to operate.

Description of drawings

FIG. 1 is a structural diagram of an optical path for optically extracting hidden information from a phase object with hidden information in the asymmetric optical information hiding technology based on visual cryptography proposed by the present invention.

Among them, 1, 2: red laser with a wavelength of 632nm; 3, 4 beam attenuators; 5, 6: collimator beam expander system; 7, 8: objects with hidden information; 9, 10: Fourier lens; 11: reflector; 12 beam splitting prism; 13: smooth white screen.

Fig. 2a is the first sub-image obtained by encrypting and encoding the image with the information "OK" to be hidden according to the "(2, 2) visual encryption scheme" through pixel expansion. ((2, 2) means that two subgraphs are generated, which can be decrypted when the two are superimposed)

Fig. 2b is the second sub-image obtained by encrypting and encoding the image with the information "OK" to be hidden according to the "(2,2) visual encryption scheme" through pixel expansion. ((2, 2) means that two subgraphs are generated, which can be decrypted when the two are superimposed)

Figure 3 is the decrypted image obtained by printing two encrypted subimages (as shown in Figure 2a and 2b) on a transparent sheet and accurately superimposing them according to the encryption of the visual cryptography scheme. The encrypted information "OK" can be extracted from the image through human recognition.

Fig. 4a is the corresponding phase distribution diagram calculated by the phase recovery algorithm of the first sub-image (Fig. 2a).

Fig. 4b is the corresponding phase distribution diagram calculated by the phase recovery algorithm of the second sub-image (Fig. 2b).

Fig. 5a is corresponding to the first sub-image (Fig. 2a) and its corresponding phase distribution diagram (Fig. 4a), the surface pattern of the binary diffractive optical element obtained after stepping the phase information according to the binary optical element design method, where the image The shade of gray represents the depth of the etched steps processed. (The original picture is in color, different colors represent the etching depth of processing)

Fig. 5b is corresponding to the first sub-image (Fig. 2b) and its corresponding phase distribution diagram (Fig. 4b), the surface pattern of the binary diffractive optical element obtained after stepping the phase information according to the binary optical element design method, where the image The shade of gray represents the depth of the etched steps processed. (The original picture is in color, different colors represent the etching depth of processing)

Figure 6a is based on the designed surface pattern of the first binary diffractive optical element (Figure 5a), the first physical image of the binary diffractive optical element obtained through mask design and manufacture, and lithography processing of quartz glass, the image is the phase An image of an object placed on a horizontal, clean white surface, similar in appearance to ordinary quartz glass.

Fig. 6b is the second binary diffractive optical element physical image obtained by designing and manufacturing the mask plate and photolithographically processing quartz glass according to the designed surface pattern of the second binary diffractive optical element (Fig. 5b). The image is the phase An image of an object placed on a horizontal, clean white surface, similar in appearance to ordinary quartz glass.

Figure 7a is an object image obtained after printing an amplitude image of a panda with bamboo leaves on transparent printing paper, and then completely pasting it on the binary diffractive optical element. This object is hidden by the method proposed in the present invention. The information carrier obtained after the information.

Figure 7b is an image of an object obtained after printing a standard Lena diagram on transparent printing paper and completely pasting it on a binary diffractive optical element. This object is an information carrier obtained by hiding information in the method proposed by the present invention .

Figure 8a is the image of the first object carrying hidden information (as shown in Figure 7a) after information extraction by the information extraction optical path system shown in Figure 1, and then received and grayscaled on the white screen. The original image is Color, where the bright part is red with laser irradiation, and the dark part without light is black.

Figure 8b is the second object carrying hidden information (as shown in Figure 7b) after the information is extracted by the information extraction optical path system shown in Figure 1, and the image is received and grayscaled on the white screen, the original image is Color, where the bright part is red with laser irradiation, and the dark part without light is black.

Figure 9 is the information extraction of two objects carrying hidden information (as shown in Figure 7a and 7b) according to the information extraction optical path system shown in Figure 1, and the two images proposed are superimposed on the white screen by coupling with a beam splitter prism The obtained image, the original image is in color, where the bright part is illuminated by laser light is red, and the dark part is black without light.

Detailed ways

In order to better understand the specific implementation process of the information hiding method proposed by the present invention, the method of encrypting information based on the "(2,2)-visual cryptography scheme" and hiding information in two phase objects will be described below in conjunction with the accompanying drawings. The collective operation process is described in detail. Because the information hiding method proposed by the present invention only uses visual cryptography to complete information encryption and dispersion, and the phase object hiding method only operates on the encrypted subgraphs independently, and has no influence on each other, so the hidden information can be obtained by "(2, 2) -Visual encryption scheme" is extended to the characteristics of "(k, n)-visual encryption scheme" to hide information in N phase objects, and K of them can extract information according to the method of the present invention, that is, the present invention proposes The information hiding method of has generalizability. For the convenience of illustration, we only specifically describe the operation of hiding information into two phase objects based on the "(2, 2)-visual cryptographic scheme".

In the process of hiding information, first determine that the information to be hidden is the letter "OK", write down the letter "OK" to be hidden and generate a black and white binary image; then follow the method of visual cryptography encryption, through pixel expansion The encoding method produces two sub-images carrying information, as shown in Figures 2a and 2b; (the image obtained after superposition of the two sub-images encoded according to the rules is shown in Figure 3, which can be directly decrypted and extracted by the human visual system to extract the information "OK ", this image is the decryption result reference of the proposed scheme of the present invention.) Secondly, according to the phase recovery algorithm portable program, calculate the phase distribution of the two sub-images respectively, and calculate the phase information distribution images as shown in Figure 4a, 4b, respectively corresponding to Sub-figures 2a and 2b; Next, according to the processing requirements of the binary diffractive optical element, the phase distribution information image (as shown in Figures 4a and 4b) is stepwise processed, and it is stepwise transformed into four uniform stepwise phase distributions Figure, which is the phase distribution in an ideal phase-type object with hidden information, and the obtained surface pattern of the object is shown in Figure 5a, 5b; finally, according to the processing method of the binary optical element, after mask design and fabrication, photolithography Processing can be processed to obtain binary diffractive optical elements, as shown in Figures 6a and 6b, these two elements are physical phase objects with information hidden through phase distribution, and their appearance is the same as that of ordinary quartz glass. Finally, print a panda with the amplitude image of the bamboo leaves and the standard Lena diagram on transparent printing paper, and completely attach it to the binary diffractive optical element to obtain the hidden information of the final phase object, and use The information hidden object generated after the amplitude image hides the phase object, as shown in Fig. 7a, 7b. As can be seen from the picture on the right, no original information can be seen on the object, which is highly concealed.

FIG. 1 is a structural diagram of an optical path for optically extracting hidden information from a phase object with hidden information in the asymmetric optical information hiding technology based on visual cryptography proposed by the present invention. Among them, 1, 2: red laser with a wavelength of 632nm; 3, 4 beam attenuators; 5, 6: collimator beam expander system; 7, 8: objects with hidden information; 9, 10: Fourier lens; 11: reflector; 12 beam splitting prism; 13: smooth white screen. In the process of information extraction, we first need to build an information extraction optical path and perform preliminary calibration.

During the process of information extraction, the Prime Minister installed two objects with hidden information (phase objects covered by amplitude images as shown in Figure 7a and 7b) correspondingly to the "7" and "8" in the deciphered optical path system shown in Figure 1. position. Turn off the laser 2 and turn on the laser 1 to get the image extracted from the first hidden information object after optical diffraction on the white screen. After grayscale, as shown in Figure 8a, the original image is red, which is the first sub-image (Fig. 2a) to restore the extracted image. Turn off the laser 1 and turn on the laser 2 to get the image extracted by the second hidden information object after optical diffraction on the white screen. After grayscale, as shown in Figure 8b, the original image is red, which is the second sub-image ( Extract the image as shown in Figure 2a).

Turn on two lasers at the same time, adjust the beam splitter so that the images extracted by optical diffraction of two objects with hidden information are coupled on the white screen to achieve image superposition, and the original information can be extracted on the white screen, and finally through the human visual system. The information "OK" of the image can be extracted, and the received image is directly grayscaled, as shown in Figure 9.

The implementation method and implementation process described above are based on visual cryptography encryption technology, using the phase distribution of phase objects to hide information, and the amplitude image to cover up phase objects and hide phase objects to achieve the purpose of hiding information with high security. The implementation of the invention is not limited to the appeal scheme. As long as the information hiding schemes, devices and systems are realized by using phase information or using phase objects carrying information to realize information hiding and using amplitude images to hide phase objects or phase information, they all fall within the scope of protection of the present invention.

Claims (7)

1. A kind of asymmetric optical information hiding technology based on visual cryptography, its concrete process comprises the following steps: Step 1: Image the information to be hidden, and encrypt and encode it into several sub-images carrying information through pixel expansion according to the visual cryptography encryption method; Step 2: Calculate the phase distribution information corresponding to each sub-graph according to the phase recovery algorithm, step the phase distribution map, and hide the information into the phase information through the processing method of the binary optical element. Step 3: Print the amplitude image on a transparent sheet, and then attach it to the phase object with hidden information, cover the phase object with the amplitude image, and finally get the object with hidden information; Step 4: Build the information extraction optical path, use the optical diffraction method to extract sub-images, and realize the superposition of the extracted sub-images through the coupling of optical elements, and finally directly extract information through human eye observation. 2. The asymmetric optical information hiding technology based on visual cryptography as used in claim 1, characterized in that, using invisible phase information and phase objects of light intensity to hide information, the concealment and security of information hiding are very high . 3. The asymmetric optical information hiding technology based on visual cryptography as used in claim 1, characterized in that the amplitude image is used to cover the phase object that hides the information, so as to realize the secondary hiding of information and further improve the hidden information safety and concealment. 4. The asymmetric optical information hiding technology based on visual cryptography used in claim 1 is characterized in that, before using the phase object to hide information, the information is encrypted and dispersed using visual cryptography encryption, which improves the The security of information hiding reduces the possibility of information exposure. 5. The asymmetric optical information hiding technology based on visual cryptography as used in claim 1 is characterized in that, using an asymmetric information hiding method, phase information hides information, and directly extracts information through optical diffraction and beam coupling, fully Taking advantage of optical parallel processing of information, the method of information extraction is easy to operate and fast in extraction speed. 6. The asymmetric optical information hiding technology based on visual cryptography as used in claims 1, 2, 3, and 4 is characterized in that the combination of multiple technologies of visual cryptography, phase hiding information, and amplitude covering phase objects The method has the advantages of multiple methods and comprehensively improves the security and concealment of information hiding. 7. The asymmetric optical information hiding technology based on visual cryptography used in claims 1 and 6 is characterized in that the technology of the present invention can also be used to legally identify phase information holders in addition to information hiding purposes. gender certification.