阅读说明：本技术 基于非对称加密的隐形涡旋结构光三维成像方法 (Invisible vortex structured light three-dimensional imaging method based on asymmetric encryption ) 是由 闫爱民 张静 吴春英 于 2021-06-21 设计创作，主要内容包括：本发明基于非对称加密的隐形涡旋结构光三维成像方法,涉及涡旋光束、结构光成像和光学图像加密技术领域。本方法包括：A步骤获取四幅待加密图像；B步骤ELGamal加密；C步骤ELGamal解密；D步骤重构被测物体图像。本发明把密码学和光学成像技术有机结合,从信息论角度研究并建立三维目标高分辨成像和实时在线加密传输的采用正交偏振隐形涡旋结构光三维成像的理论模型和相移干涉加密理论,研究三维图像信息的获取和加密安全性模型。具有结构简单,易于实现自动化、大量程,非接触,速度快,精度高,安全性好等优点,特别在三维物体的信息传输方面提供了新的技术手段。将在身份认证、高分辨成像和保密通信等领域具有广阔的应用前景。(The invention discloses an invisible vortex structured light three-dimensional imaging method based on asymmetric encryption, and relates to the technical field of vortex light beams, structured light imaging and optical image encryption. The method comprises the following steps: a, acquiring four images to be encrypted; b, ELGamal encryption; step C, ELGamal decryption; and D, reconstructing an image of the measured object. The invention organically combines cryptography and optical imaging technology, researches and establishes a theoretical model of three-dimensional target high-resolution imaging and real-time online encryption transmission and adopting orthogonal polarization invisible vortex structured light three-dimensional imaging and a phase shift interference encryption theory from the information theory angle, and researches an acquisition and encryption security model of three-dimensional image information. The device has the advantages of simple structure, easy realization of automation, wide range, non-contact, high speed, high precision, good safety and the like, and particularly provides a new technical means in the aspect of information transmission of three-dimensional objects. The method has wide application prospect in the fields of identity authentication, high-resolution imaging, secret communication and the like.)

1. The three-dimensional imaging method based on the asymmetric encrypted invisible vortex structured light is characterized by comprising a laser (1), a half-wave plate (2), a polarization beam splitter (3), a first beam expander (4-1), a second beam expander (4-2), a first reflector (5-1), a second reflector (5-2), a first spatial light modulator (6-1), a second spatial light modulator (6-2), a polarization beam combiner (7), a transmitting telescope (8), a measured object (9), a receiving telescope (10), an 1/4 wave plate (11), a four-step phase shift modulator (12) and a computer (13) which are connected in an optical path mode.

2. The asymmetric encryption based invisible vortex structured light three-dimensional imaging method as claimed in claim 1, characterized by comprising the following steps:

a, acquiring four images to be encrypted;

b, ELGamal encryption;

step C, ELGamal decryption;

and D, reconstructing an image of the measured object.

3. The asymmetric encryption based invisible vortex structured light three-dimensional imaging method as claimed in claim 2, wherein the step A of obtaining four images to be encrypted further comprises the following steps:

step A1: after passing through a half-wave plate (2), a light beam emitted by a laser (1) is divided into two beams of light with orthogonal polarization states, namely horizontal polarized light and vertical polarized light, by a polarization beam splitter (3);

step A2: after being expanded by the first beam expander (4-1) and the first reflector (5-1), the horizontal polarized light passes through the first spatial light modulator (6-1) loaded with the holographic grating to generate vortex light with topological charge of + l and then irradiates the polarization beam combiner (7);

step A3: after the vertical polarized light is expanded by the second beam expander (4-2) and the second reflector (5-2), vortex light with topological charge of-l is generated by the second spatial light modulator (6-2) carrying the holographic grating and is irradiated on the polarization beam combiner (7) to be combined with the horizontal polarized light to form invisible vortex structured light with orthogonal polarization directions;

the values of the topological charge numbers + l and-l are integers or fractions;

step A4: irradiating the measured object (9) through a transmitting telescope (8);

step A5: the light reflected by the object to be measured (9) passes through a receiving telescope (10), an 1/4 wave plate (11) and a four-step phase shift modulator (12) to obtain four images I to be encrypted₀、I_π、

4. The asymmetric encryption based invisible vortex structured light three-dimensional imaging method as claimed in claim 2, wherein said B step is to combine four images I to be encrypted₀、I_π、Respectively as plaintext m of ELGamal encryption algorithm;

the ELGamal encryption algorithm is an algorithm established based on a discrete logarithm problem and consists of three parts, namely key generation, encryption and decryption;

further comprising the steps of:

b1: the recipient and the sender share information (p, alpha, beta) disclosing the parameters,

wherein p is a randomly selected prime number; alpha is a finite field Z_PA generator of (1); b is a private key which can be a fingerprint, a face image and an iris biological characteristic image, and an integer matrix is obtained through processing; beta is a public key, and is defined by^bmod (p) represents;

b2: for plaintext m, randomly selecting a random number k epsilon [1, p-2 ∈ ]]Calculating gamma-alpha^kmod (p) and δ ═ m β^kmod (p), thereby obtaining a ciphertext of c ═ γ, δ.

5. The asymmetric encryption based invisible vortex structured light three-dimensional imaging method as claimed in claim 2, wherein the step C ELGamal decryption further comprises the steps of:

after receiving the ciphertext c ═ y, δ, the receiver calculates m ═ δ/γ using the private key b by the computer (13)^bmod (p) to obtain four decrypted images.

6. The asymmetric encryption based invisible vortex structured light three-dimensional imaging method as claimed in claim 2, wherein said D step reconstructs an image of the object to be measured, further comprising the steps of:

d1: the decrypted image obtained in the computer (13) is denoted as I ═ R (a + Bcos phi),

wherein R represents the uneven reflectivity of the surface of the object;

a represents the background intensity;

B/A represents the contrast of the grating stripes;

1/4, the phase shift amount is pi/2, because of each moving period of the grating;

the phase can be expressed as

D2: after the phase is unfolded, h ═ LT Δ Φ)/(2 pi d + T Δ Φ) can be obtained according to a trigonometric principle, and a height value of the object is obtained;

wherein L represents the distance of the camera from the reference plane; t represents the period of the projection grating; d is the distance between the center of the camera and the center of the projection system; and delta phi represents the difference between the phase value of the measured object and the phase value of the reference plane.

Technical Field

The invention relates to the technical field of vortex light beam, structured light imaging and optical image encryption, in particular to an invisible vortex structured light three-dimensional imaging method based on asymmetric encryption.

Background

With the wide application of the internet and various information transmission technologies, the security of information in communication and storage has become a research hotspot today. Image encryption is an important research direction in the field of information security, and mainly comprises two main categories of traditional image encryption technology based on mathematical theory and novel image encryption technology based on non-mathematical theory. Among them, encrypting an image using physical parameters is a novel image encryption technology, and shows superiority in some fields, especially an optical image encryption technology, and has received increasing attention in recent years. Compared with the traditional electronic signal processing method, the optical information security technology has the unique advantages in the aspects of processing speed, encryption dimension, implementation cost, security, inherent parallel processing characteristic and the like. Information security technology based on optical theory has the advantages, and researchers have conducted a lot of research in recent years to propose various algorithms and structures for optical image encryption. However, most optical image encryption methods use a two-dimensional target as an encryption object, and cannot measure depth information of the target, and particularly cannot perform high-resolution imaging on a remote three-dimensional target, which makes it difficult to widely apply an optical image encryption technology to a real three-dimensional scene. The emergence of the laser three-dimensional imaging technology provides a new technical means for people.

On the other hand, many optical image encryption methods belong to the category of symmetric encryption, and are linear systems in nature, and the linear problem of the encryption system can leave serious potential safety hazard for the system. For the system security loophole existing in the linear system, researchers further propose a non-linear or asymmetric encryption scheme to enhance the security of the system. Penhang proposes known plaintext attack and ciphertext-only attack based on a phase recovery algorithm, and points out that the linear nature of a DRPE encryption system causes security holes. And proposes an optical image encryption architecture based on phase truncation, so as to be able to generate a decrypted phase plate that is completely different from the encryption key. The Monause front proposes an asymmetric encryption scheme combining two-step phase-shift interference and a public key encryption algorithm, and commonly used public key algorithms include Rivest-Shamir-Adleman (RSA) algorithm, Elliptic Curve Cryptography (ECC) algorithm and the like. The ELGamal encryption algorithm is a public key cryptosystem based on discrete logarithm problem in finite field and adopts an asymmetric digital encryption method, and is an internationally recognized ideal public key cryptosystem. The current public key encryption is mainly based on a one-way trapdoor function, namely a function with easy forward calculation and extremely difficult inverse calculation. In 1976, Whirefield Diffie and Matin Hellman proposed the idea of public key cryptography. In 1985, ELGamal proposed an ELGamal public key cryptosystem, and the security of the ELGamal public key cryptosystem depends on the difficulty degree of discrete logarithm solution. In recent years, the ELGamal encryption algorithm is widely applied to the network security digital encryption technology, but is rarely applied to the field of optical image encryption.

Disclosure of Invention

The invention aims to provide an invisible vortex structured light three-dimensional imaging method based on asymmetric encryption aiming at the defects and shortcomings in the existing object three-dimensional information transmission technology, firstly two beams of invisible vortex structured light with orthogonal polarization states and topological charge numbers of + l and-l are generated, the two beams of invisible vortex structured light irradiate the surface of an object to be detected and then are reflected, the reflected light is received by a receiving telescope and then is modulated by a four-step phase shift modulator to obtain four images to be encrypted, and then an encryption ciphertext is obtained by an Elgamal encryption processor; in the decryption process, an ELGamal decryption processor is used for decrypting to obtain four decrypted images, and finally, the images of the measured object can be reproduced through a structured light three-dimensional imaging algorithm.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention relates to an invisible vortex structured light three-dimensional imaging method based on asymmetric encryption, which is characterized by comprising a laser, a half-wave plate, a polarization beam splitter, a first beam expander, a second beam expander, a first reflecting mirror, a second reflecting mirror, a first spatial light modulator, a second spatial light modulator, a polarization beam combiner, a transmitting telescope, a measured object, a receiving telescope, an 1/4 wave plate, a four-step phase shift modulator and a computer which are connected in a light path mode.

Further, the invention relates to an invisible vortex structured light three-dimensional imaging method based on asymmetric encryption, which comprises four links of firstly obtaining four images to be encrypted, secondly carrying out ELGamal encryption, thirdly carrying out ELGamal decryption and fourthly reconstructing an image of a measured object, and specifically comprises the following detailed steps:

acquiring four images to be encrypted:

after passing through a half-wave plate, a light beam emitted by the laser is divided into two beams of light with orthogonal polarization states by a polarization beam splitter, namely horizontal polarized light and vertical polarized light;

the horizontal polarized light passes through the first beam expander to be expanded and the first reflector, then passes through a first spatial light modulator loaded with the holographic grating to generate vortex light with the topological charge number of + l, and then is irradiated onto the polarization beam combiner;

the vertical polarized light is expanded by the second beam expander and the second reflector, then passes through the second spatial light modulator loaded with the holographic grating to generate vortex light with topological charge number-l, and the vortex light irradiates the polarization beam combiner and is combined with the horizontal polarized light to form invisible vortex structure light with orthogonal polarization directions, and the invisible vortex structure light irradiates a measured object after passing through the transmitting telescope;

the values of the topological charge numbers + l and-l are integers or fractions;

the light reflected by the object to be measured passes through the receiving telescope, 1/4 wave plate and four-step phase shift modulator to obtain four images I to be encrypted₀、I_π、

The invisible vortex structured light is characterized in that two beams of light are in orthogonal polarization states, so that no interfering structured light pattern can be seen on a target plane and can be detected only after polarization rotation at a receiving end, the invisible vortex structured light is called as invisible vortex structured light, and the size, the position, the phase difference, the direction and the like of the two polarized orthogonal beams are controlled to obtain invisible vortex structured light patterns in different shapes.

ELGamal encryption:

four images I to be encrypted₀、Iπ、Respectively as plaintext m of ELGamal encryption algorithm;

the ELGamal encryption algorithm consists of three parts of key generation, encryption and decryption, and is an algorithm established based on a discrete logarithm problem.

First, the receiver and the sender share information (p, α, β) of the public parameters,

wherein p is a randomly selected prime number;

alpha is a finite field Z_PA generator of (1);

b is a private key which can be a fingerprint, a face image and an iris biological characteristic image, and an integer matrix is obtained through processing;

beta is a public key and can be represented by beta ═ alpha^bmod (p).

Then, for the plaintext m, the random number k epsilon [1, p-2 ] can be arbitrarily selected]To calculate gamma-alpha^kmod (p) and δ ═ m β^kmod (p), from which the ciphertext c ═ γ, δ is obtained;

③ ELGamal decipher:

after receiving the ciphertext c ═ y, δ, the receiver calculates m ═ δ/γ using the private key b by the computer^bmod (p), four decrypted images are obtained.

Fourthly, reconstructing an image of the measured object:

the resulting decrypted image in the computer may be denoted as I ═ R (a + Bcos phi),

wherein R represents the uneven reflectivity of the surface of the object;

a represents the background intensity;

B/A represents the contrast of the raster pattern;

since the grating moves 1/4 cycles each time, the amount of phase shift is π/2.

The phase can be expressed as:

after the phase is expanded, the phase can be obtained according to the triangle principle

h＝(LTΔφ)/(2πd+TΔφ)，

Obtaining the height value of the object, wherein L represents the distance between the camera and the reference plane; t represents the period of the projection grating; d is the distance between the center of the camera and the center of the projection system; and delta phi represents the difference between the phase value of the measured object and the phase value of the reference plane.

In summary, the invention first passes four images to be encrypted through an E1 gamma encryption processor to obtain an encrypted ciphertext; in the decryption process, an ELGamal decryption processor is used for decrypting to obtain four decrypted images, and finally, the images of the object to be detected are reproduced through a structured light three-dimensional imaging algorithm. An ELGamal encryption algorithm is introduced into a structured light three-dimensional imaging algorithm, so that a safer solution is provided for the transmission of three-dimensional object information. The method has wide application prospect in the fields of identity authentication, high-resolution imaging, secret communication and the like.

Drawings

FIG. 1 is a block diagram of an optical three-dimensional imaging method of an invisible vortex structure based on asymmetric encryption;

description of the drawings: the device comprises a laser 1, a half-wave plate 2, a polarization beam splitter 3, a first beam expander 4-1, a second beam expander 4-2, a first reflecting mirror 5-1, a second reflecting mirror 5-2, a first spatial light modulator 6-1, a second spatial light modulator 6-2, a polarization beam combiner 7, a transmitting telescope 8, a measured object 9, a receiving telescope 10, a 1/4 wave plate 11, a four-step phase shift modulator 12 and a computer 13.

FIG. 2 is a block diagram of a process for reconstructing an image of a measured object according to an embodiment of the present invention;

FIG. 3 is an image of an object under test in an embodiment of the invention;

fig. 4(a) - (d) are four images to be encrypted in an embodiment of the present invention;

FIGS. 5(a) - (d) are images of four ciphertexts in an embodiment of the present invention;

FIGS. 6(a) - (d) are four decrypted images in an embodiment of the present invention;

fig. 7 is an image of a measured object after three-dimensional reconstruction in the embodiment of the present invention.

Detailed Description

The invention is further described below with reference to the figures and examples.

The invention relates to an asymmetric encryption-based invisible vortex structured light three-dimensional imaging method (as shown in an attached drawing 1), which is characterized by comprising a laser 1, a half-wave plate 2, a polarization beam splitter 3, a first beam expander 4-1, a second beam expander 4-2, a first reflector 5-1, a second reflector 5-2, a first spatial light modulator 6-1, a second spatial light modulator 6-2, a polarization beam combiner 7, a transmitting telescope 8, a measured object 9, a receiving telescope 10, a 1/4 wave plate 11, a four-step phase shift modulator 12 and a computer 13 which are connected in an optical path mode.

The invention relates to an asymmetric encryption-based invisible vortex structured light three-dimensional imaging method, which comprises the following steps (as shown in the attached figure 2):

a, acquiring four images to be encrypted;

b, ELGamal encryption;

step C, ELGamal decryption;

and D, reconstructing an image of the measured object.

The method specifically comprises the following detailed steps:

the step A of obtaining four images to be encrypted further comprises the following steps:

step A1: after passing through a half-wave plate 2, a light beam emitted by a laser 1 is divided into two beams of light with orthogonal polarization states, namely horizontal polarized light and vertical polarized light, by a polarization beam splitter 3;

step A2: the horizontal polarized light is expanded by a first beam expander 4-1 and passes through a first reflector 5-1, and then is irradiated on a polarization beam combiner 7 by vortex light with topological charge number of + l generated by a first spatial light modulator 6-1 loaded with a holographic grating;

step A3: the vertical polarized light is expanded by a second beam expander 4-2 and a second reflecting mirror 5-2, then passes through a second spatial light modulator 6-2 loaded with holographic grating to generate vortex light with topological charge number-l, and the vortex light irradiates a polarization beam combiner 7 to be combined with the horizontal polarized light to form invisible vortex structure light with orthogonal polarization directions;

the values of the topological charge numbers + l and-l are integers or fractions;

step A4: irradiating the measured object 9 through the transmitting telescope 8;

step A5: the light reflected by the object to be measured 9 passes through a receiving telescope 10, a 1/4 wave plate 11 and a four-step phase shift modulator 12 to obtain four images I to be encrypted₀、I_π、

The step B of ELGamal encryption further comprises the following steps:

b1: the recipient and the sender share information (p, alpha, beta) disclosing the parameters,

wherein p is a randomly selected prime number; alpha is a finite field Z_PA generator of (1); b is a private key which can be a fingerprint, a face image and an iris biological characteristic image, and an integer matrix is obtained through processing; beta is a public key, and is defined by^bmod (p) represents;

b2: for plaintext m, randomly selecting a random number k epsilon [1, p-2 ∈ ]]Calculating gamma-alpha^kmod (p) and δ ═ m β^kmod (p), thereby obtaining a ciphertext of c ═ γ, δ.

And C, the ELGamal decryption further comprises the following steps:

after receiving the ciphertext c ═ y, δ, the receiver calculates m ═ δ/γ using the private key b by the computer 13^bmod (p), i.e. four decrypted images are obtained.

And D, reconstructing an image of the measured object, and further comprising the following steps:

d1: the resulting decrypted image in the computer 13 is denoted I ═ R (a + Bcos phi),

wherein R represents the uneven reflectivity of the surface of the object;

a represents the background intensity;

B/A represents the contrast of the raster pattern;

1/4, the phase shift amount is pi/2, because of each moving period of the grating;

the phase can be expressed as

D2: after the phase is unfolded, h ═ LT Δ Φ)/(2 pi d + T Δ Φ) can be obtained according to the principle of triangulation, and the height value of the object is obtained;

wherein L represents the distance of the camera from the reference plane; t represents the period of the projection grating; d is the distance between the center of the camera and the center of the projection system; and delta phi represents the difference between the phase value of the measured object and the phase value of the reference plane.

One embodiment of the invention:

first, by taking the case that the horizontally polarized light passes through the first spatial light modulator to generate the vortex rotation with the topological charge of + l (l ═ 0), that is, the gaussian beam and the vertically polarized light pass through the second spatial light modulator to generate the vortex rotation with the topological charge of-l (l ═ 0), that is, the gaussian beam, the four generated images sequentially irradiate the object to be measured (as shown in fig. 3).

The structured light is modulated by the object to be measured to generate four images to be encrypted (as shown in fig. 4(a) - (d)).

The four images to be encrypted are subjected to ELGamal encryption (as shown in fig. 5(a) - (d)), and are decrypted by a decryption algorithm to obtain four decrypted images (as shown in fig. 6(a) - (d)).

And finally, recovering the image of the measured object by using a structured light three-dimensional imaging algorithm (as shown in figure 7).

Accordingly, the present invention can be summarized as follows:

(1) the method for three-dimensional imaging of the invisible vortex structure light is used for three-dimensional reconstruction of an object, and the influence of environment stray light on an experiment can be effectively overcome and the imaging quality can be improved by introducing the invisible vortex structure light. Meanwhile, a phase shift method is adopted to provide a bridge for the combination of the invisible vortex structured light three-dimensional imaging method and the Elgamal encryption method, and compared with other methods, the phase shift method is the most effective and reliable method for obtaining the spatial three-dimensional information of the object.

(2) The ELGamal encryption method is a typical asymmetric encryption algorithm, and can be used for encrypting and decrypting four images generated by four-step phase shift, so that the encryption security of an object can be greatly improved. Moreover, the ELGamal algorithm has a solid mathematical basis as a theoretical support, so that the safety is ensured.

In summary, the invention is a structured light three-dimensional imaging method based on the combination of invisible vortex structured light and ELGamal encryption algorithm, combines the cryptography and the optical imaging technology organically, researches and establishes a theoretical model of three-dimensional target high-resolution imaging and real-time online encryption transmission by adopting orthogonal polarization invisible vortex structured light three-dimensional imaging and a phase-shift interference encryption theory, and researches the acquisition of three-dimensional image information and an encryption security model. The method has the advantages of simple structure, capability of effectively overcoming environmental stray light, easiness in realization of automation, wide range, non-contact, high speed, high precision, good safety and the like, and provides a new technical means for solving the problems of internet information safety and particularly information transmission of three-dimensional objects. The method has wide application prospect in the fields of identity authentication, high-resolution imaging, secret communication and the like.