CN111383292A

CN111383292A - Optical information hiding technology based on visual password dual-wavelength multiplexing

Info

Publication number: CN111383292A
Application number: CN201910365563.3A
Authority: CN
Inventors: 李桂林; 祝玉鹏; 杨栋宇; 马锐; 于韬; 孙鑫凯; 史祎诗
Original assignee: University of Chinese Academy of Sciences
Current assignee: University of Chinese Academy of Sciences
Priority date: 2019-05-01
Filing date: 2019-05-01
Publication date: 2020-07-07

Abstract

The invention discloses an optical information hiding technology based on visual cryptography dual-wavelength multiplexing. On the basis of the visual password, secret information is encoded into a diffraction pattern and a diffraction pattern generated by calculation of the diffraction pattern by using an expanded visual password encoding scheme, then two pieces of diffraction pattern information are converted into a pure phase diffraction optical element by using a GS algorithm, the pure phase diffraction optical element is received at a specific position by irradiating the diffraction element with laser with two specific wavelengths, and decryption information can be obtained by human eyes. The invention uses the pure phase optical diffraction element as a hidden carrier, two specific wavelengths as decryption keys, and an optical system is realized by diffraction of the diffraction element, so that the method has the advantages of good concealment, strong anti-noise capability, high safety and no need of alignment, is simple to operate, effectively solves the problems of poor concealment, complex system, more application limitations and the like in the prior art, and can be applied to the field of information encryption with high safety and system integration.

Description

Optical information hiding technology based on visual password dual-wavelength multiplexing

Technical Field

The invention relates to an optical information hiding technology, in particular to a technology which uses a pure phase diffraction optical element as a hiding carrier, utilizes two lasers with specific wavelengths to simultaneously irradiate a diffraction element and obtains hidden information at a specific position through diffraction action.

Background

The optical information hiding has a wide research prospect as an important research direction of optical information safety. Optical information hiding typically embeds secret information into a redundant carrier through optical transformation or other processes, or transforms the secret information into meaningless information such as white noise through a key. The most classical optical information hiding techniques are the double random phase encoding proposed by refgier and Javidvi in 1995, which uses two random phases as keys to transform secret information into meaningless complex amplitudes, see (Opt Lett 1995; 20: 767-9), followed by work on the optimization of the deficiencies of this scheme, such as quantization of the encrypted complex ciphertext to reduce its discrete real number, fractional fourier transform or fresnel transform instead of fourier transform, and another way to embed the secret information into a given image to achieve information hiding. In recent years, various optical systems have been tried for optical information hiding, including off-axis holography, cascaded phase mask structures, joint transform correlators, ghost imaging systems, and stacked imaging systems, and the optical information hiding has the advantages of parallelization, high-speed processing, suitability for multi-dimensionality, and unique appeal in the field of information security.

Visual cryptography is a technology related to image encryption, and provides a scheme for dividing an image carrying information to be encrypted into a plurality of encrypted sub-images, and acquiring the encrypted information by human eyes without any cryptographic calculation as long as a specified number of sub-images are accurately superposed. In 1994, Moni. Naor and Adi. Shamir formally proposed visual cryptography and carried out detailed theoretical elucidation, marking visual cryptography schemes as an important branch of cryptography research, see (Eurocrypt 1994 (1): 1-12, 1994). On the basis of a random grid encryption technology, visual cryptography realizes an encryption function by using a mode that a plurality of pixel point arrays jointly form a pixel dot matrix block, and finally generates an encryption subgraph of an encryption scheme. This scheme can be described as a "(k, n) -visual cryptography scheme", i.e. an image carrying encrypted information is encoded into n encrypted sub-images according to rules, providing that any k participants can decrypt the information (k is greater than 2 and less than or equal to n), assigning the sub-images to the n cryptographic scheme participants. When any k participants align and superpose the subgraphs, decryption can be completed, decryption information can be directly obtained through human eyes, and any participant smaller than k cannot complete decryption.

The subject group uses a visual password for optical information hiding in 2017, secret information is converted into a group of diffractive optical element keys in the hiding process through a visual password coding scheme, the diffractive optical elements are only required to be irradiated by laser in the extracting process, the obtained patterns are superposed together, and the secret information is directly extracted through the contact function of human eyes, see (J. Opt. 19(2017) 115703 (10 pp)), the visual password coding scheme is most different from other optical encryption schemes in that the scheme is asymmetric in encryption and decryption, and the decryption only needs simple superposition and has the advantages of rapidness and simplicity.

While the existing visual password scheme has the above advantages and characteristics, the existing visual password scheme also has some disadvantages:

1. the concealment is poor, the hidden carrier of the existing visual password in optical concealment is a binary random distribution structure with obvious rules, although no significance is provided, the characteristics are obvious, and the concealment is poor;

2. the application limit is more, the existing scheme is bound by a visual password scheme, the information can be provided for human eyes to obtain information only by accurate alignment decryption, and the information is easily interfered by alignment, so that more limit is caused to practical application;

3. the optical system is complicated, and the existing visual passwords hide a plurality of carriers in optical hiding, so that the complexity of the optical system is increased.

Disclosure of Invention

The invention aims to overcome the defects of the existing visual password in optical information hiding, solve the problems that the hidden information carrier generated by the visual password coding has poor secrecy, the number of the hidden carriers is large, the decryption hiding result needs to be combined with high requirements on the stability of a system and the like, and compared with the traditional optical information hiding, the invention utilizes a pure phase diffraction optical element as the hidden carrier and uses two wavelengths as decryption keys to simplify the structure of an optical information hiding system, so that the decryption is simpler and faster, and the robustness of the system is improved.

The object of the invention can be achieved by the following technical measures.

(1) Based on visual password, hidden information is coded by using expanded visual password coding scheme

(the function is a binary function) encoding into a diffraction Pattern

And a diffraction pattern generated by calculation from the diffraction pattern

In the real-valued function (the function), the expanded visual coding scheme is as follows:

the scheme is an expansion on a (2, 2) visual cryptography coding scheme of Moni. Naor and Adi. Shamir in 1994, wherein the (2, 2) visual cryptography coding scheme is carried out on the basis of pixels, one pixel of secret information is coded on two keys, the pixel on the 2 keys is expanded into 2 pixels, the structure of the pixel is 0, 1 or 1, 0 arrangement, the arrangement of the pixels at different positions is random, and the expanded visual cryptography scheme is that

1. Secret information

Expanding the image into two binary images according to the expansion scheme of (2, 2)

And

；

2. diffraction pattern

Is divided into

The pixels in the regions with the same number are divided into three classes according to the gray value to form three sets, wherein the pixels in each region are the same, namely the pixels in the former are pixel extensions of the latter and are in one-to-one correspondence in position, and the pixels in each region are divided into three classes according to the gray value to form three sets, wherein the three sets are formed

Is a large set of,

Is a set of intermediate values,

Is a small set of values and satisfies that for any s, t there is

,

The number of pixels of the large value set and the small value set is the same;

3、

each of the regions and

the pixels of (a) correspond to (b),

and

is that

Pixel spread of (2) pixels and

correspond to pixels of (i.e. are

Each of the regions and

and

every 2 pixels corresponds. The foregoing says that

And

each 2 pixels of (2) has a 0, 1 or 1, 0 structure

And

when the corresponding positions have the same structure

In the area and

are distributed in the same way if the structures are different

The distribution in the area is

Large set of values in this region

And small value set

Elements in the two sets are arranged according to sizes and are subjected to one-to-one position conversion;

by means of which secret information can be encoded

Encoding into diffraction patterns

And calculating the resulting diffraction pattern

In (1).

(2) Using the GS algorithm, the diffraction patterns are

And diffraction patterns

Conversion to different wavelengths

、

Illuminating optical elements of the same phase

(the gradient can be designed as required) diffracts to the same location to receive the resulting diffraction pattern. The specific process is as follows

1. Guessing phase distribution function of optical element

At a wavelength of

Diffraction under laser to obtain a diffraction pattern

Here, the

。

Is a wavelength of

Through a focal distance of

To a back focal point of the Fourier lens

Fresnel transformation of (1);

2. the complex amplitude obtained by diffraction

With phase left and amplitude from current

Calculated diffraction pattern of

Instead, then at a wavelength of

Is subjected to inverse laser down-conversion to obtain

Here, the

，

Is a wavelength of

The inverse of the above-described diffraction process of (a),

is a phase function;

3. taking phase from complex amplitude obtained by inverse diffraction, and graduating to obtain new optical element phase distribution function

Repeating the

steps

1 and 2 until convergence;

the phase optical element can be obtained by the steps

。

(3) The process of decrypting the hidden information only needs to use the wavelength of

And

laser beam simultaneously irradiating optical element

At off focal distance

Can obtain the hidden information

The hidden information can be obtained through the visual password

。

Compared with the prior art, the invention has the following advantages:

(1) the hidden carrier is a pure phase diffraction optical element, the intensity of pure phase information is invisible, the concealment of an encryption scheme is improved, and meanwhile, compared with the existing optical information hiding method with visual passwords, the hidden carrier only needs a plurality of carriers, the number of the carriers is reduced, and the structure of an optical system is simplified;

(2) the method uses the phase information of the pure phase plate for decryption, and because the pure phase plate only has the phase information and completes decryption through diffraction, the system has high noise tolerance and strong anti-noise capability, namely the scheme has good robustness;

(3) the invention adopts an expanded visual password coding scheme, the hidden information can be decrypted only by simultaneously irradiating specific double wavelengths, the requirement on the wavelengths is strict, meanwhile, the diffraction pattern obtained by irradiating one specific wavelength is in accordance with the random distribution of the visual password, and no information related to the hidden information exists, so that the safety is very high;

(4) the hardware system adopted for realizing the invention is simple, has good integratability and is very convenient for practical application.

The optical information hiding technology based on the vision password dual-wavelength multiplexing disclosed by the invention is suitable for encryption application occasions with high safety, strong robustness and high system integratability.

Drawings

Fig. 1 is an optical path diagram for decrypting hidden information in an optical information hiding technique based on visual cryptography dual wavelength multiplexing according to the present invention.

The device comprises a laser 1 with the wavelength of 632nm, a laser 2 with the wavelength of 450nm, a beam splitter prism 3, an optical diffraction element 4, a Fourier lens 5, a CCD receiving unit 6 and a computer 7.

Fig. 2 is a binary image with 128 × 128 pixels of the secret information "a" to be hidden in the invention.

Fig. 3 is an 8-gradient phase profile of the phase diffractive optical element (4 in fig. 1) generated by the matlab program code of the present invention, with pixels 640 x 640.

Fig. 4a is a diffraction pattern of the phase distribution of fig. 3 with a wavelength of 632nm illuminated under the optical path structure of fig. 1, with pixels 640 x 640.

Fig. 4b is a diffraction pattern from fig. 3 of a distribution of illumination phases at a wavelength of 450nm under the optical path structure of fig. 1, with pixels 640 x 640.

Fig. 5 shows that the pixels are 640 x 640 as a result of superimposing the letters "a" of hidden information obtained by the vision of human eyes, which is obtained by simultaneously irradiating the diffraction optical element of the phase distribution of fig. 3 with laser light of wavelength 632nm and wavelength 450nm, and receiving the laser light by the CCD at a defocus distance of 3 cm.

Fig. 6 shows the decryption result obtained by computer simulation of the diffractive optical element obtained above, i.e., fig. 3, with the wavelength 440nm and the wavelength 632nm, and the pixel is 640 x 640.

Fig. 7 shows that the CCD is decrypted by changing the position 3cm out of focus to 2cm, and the pixel is 640 x 640.

Detailed Description

In order to better explain the implementation process of the present invention, the operation process is described in detail below with reference to the attached drawings.

The optical path structure comprises a laser with the wavelength of 1.632 nm, a laser with the wavelength of 2.450 nm, a beam splitter prism 3, an optical diffraction element 4, a Fourier lens 5, a CCD receiving unit 6 and a computer 7. The 8-gradient phase structure adopted by the optical diffraction element is positioned at the focal length position of the Fourier lens; the CCD receiving unit is located at a fixed position before (or after) focus.

The encrypted information "a" is first determined, the image carrying the information, e.g. 2, is acquired and encoded into the two sub-images 4a, 4b using software. The method comprises the following specific steps:

(1) based on the visual password principle, the visual password coding scheme is expanded, and the secret information is decomposed into two diffraction patterns. One diffractogram is that of the laser-illuminated random 8-gradient phase optical element of FIG. 1 at a wavelength of 632nm at a 3cm off-focus distance after passing through a Fourier lens of 8cm focal length. The other diffraction pattern is generated by expanded visual code;

(2) the diffractive optical element is obtained by using the GS algorithm. The amplitude of the complex amplitude obtained by 632nm laser is replaced by a diffraction pattern generated by expanding visual code, the complex amplitude is obtained by inverse diffraction with the wavelength of 450nm, the complex amplitude is changed into 1, the phase is changed into 8 gradients, a new diffraction element is obtained, and the process is repeated for 20 times to obtain the phase distribution of the convergent diffraction optical element as shown in figure 3.

Fig. 4a is a diffraction diagram of the phase distribution as shown in fig. 3 when the light path structure as shown in fig. 1 is irradiated at a wavelength of 632nm, fig. 4b is a diffraction diagram of the phase distribution as shown in fig. 3 when the light path structure as shown in fig. 1 is irradiated at a wavelength of 450nm, the decrypted hidden information is that laser with the wavelength of 632nm and laser with the wavelength of 450nm simultaneously irradiates the diffraction optical element with the phase distribution as shown in fig. 3, the CCD receives the information at a fixed diffraction distance, and the character "a" of the hidden information can be obtained through the vision of human eyes, namely, the superposition result.

The diffraction optical element obtained above was irradiated with computer-simulated light of 440nm and 632nm in wavelength to obtain the decryption result shown in fig. 6. The decryption result is obtained by changing the CCD focal distance position 3cm to 2cm as shown in FIG. 7.

The method and the example are obtained by expanding the visual password coding scheme and combining the GS algorithm to convert the secret information into the phase diffraction optical element on the basis of the existing visual password scheme, using different wavelengths as keys and decrypting the secret information by using the optical path system and the decryption method provided by the invention. The practice of the present invention is not limited to the above-described embodiments. Any method, device and system that encode secret information into a diffractive optical element using the above-mentioned visual cryptography encoding scheme and GS algorithm and hide the secret information using the above-mentioned photoelectric method or diffraction function, as long as the two wavelengths are used as keys, are within the scope of the present invention.

Claims

1. A technology for hiding optical information based on visual cryptography dual-wavelength multiplexing comprises the following steps:

the first step, based on the visual password, utilizing an expanded visual password coding scheme to code hidden information into a diffraction pattern and another diffraction pattern generated by coding the diffraction pattern by a computer;

secondly, two pieces of diffraction pattern information are respectively converted into specific wavelengths by utilizing a GS algorithm

、

The laser is diffracted at the same position by the same pure phase diffraction optical element to obtain a diffraction pattern;

third, the hidden information is decrypted and the specific wavelength is used

、

The laser irradiates the same pure phase diffraction optical element to obtain a diffraction pattern at a specific position, and hidden information can be obtained through human eyes.

2. Optical information hiding technique based on visual cryptography dual wavelength multiplexing as used in claim 1, characterized in that the hiding carrier used is a phase-only diffractive optical element with excellent hiding.

3. The optical information hiding technique based on visual cryptography two-wavelength multiplexing as claimed in claims 1, 2, wherein the hidden information is a superposition of diffraction patterns obtained by irradiating the diffractive optical element with laser light of two specific wavelengths, the two diffraction patterns being ordinary diffraction patterns, and a single diffraction pattern having no information related to the hidden information.

4. The optical information hiding technique based on visual cipher dual wavelength multiplexing as used in claims 1, 2, 3, characterized in that the two diffraction patterns obtained are encoded by an extended visual cipher coding scheme, and the extended visual cipher coding scheme is obtained on the basis of a visual cipher, and the diffraction patterns have the same security as the visual cipher key.

5. The optical information hiding technique based on optical cipher dual wavelength multiplexing as claimed in claims 1, 2, 3, wherein the obtained hidden carrier diffractive optical element is obtained by GS algorithm, which has the advantage of simple implementation, has good compatibility with existing design methods of diffractive optical elements, and facilitates the process implementation.

6. The optical information hiding technique based on visual cryptography dual wavelength multiplexing as claimed in claims 1, 2, 3, 4, 5, wherein the invention is realized by designing the diffractive optical element based on visual cryptography in combination with dual wavelength multiplexing, and has both advantages, and avoids both defects, and has extremely high concealment, security and practicability.