CN111385435A

CN111385435A - Multi-image optical hiding system based on visual password

Info

Publication number: CN111385435A
Application number: CN201910245713.7A
Authority: CN
Inventors: 于韬; 杨栋宇; 马锐; 孙鑫凯; 祝玉鹏; 李桂林; 马金戈; 史祎诗
Original assignee: University of Chinese Academy of Sciences
Current assignee: University of Chinese Academy of Sciences
Priority date: 2019-03-28
Filing date: 2019-03-28
Publication date: 2020-07-07

Abstract

The invention discloses a multi-image hiding system based on a visual password. The system encrypts multiple images based on a visual password scheme to obtain multiple shared images, then uses a phase recovery algorithm to design a diffractive optical element, so that different shared images are reproduced at different positions of a rear space after the obtained diffractive optical element is irradiated by laser, and corresponding shared images are aligned and overlapped to decrypt secret information. The invention uses the diffractive optical element to hide a plurality of shared images obtained after encryption by a visual password scheme, effectively utilizes the controllability of the diffractive optical element on the three-dimensional light field, and realizes the hiding of a plurality of encrypted information.

Description

Multi-image optical hiding system based on visual password

Technical Field

The invention relates to a multi-image hiding system, in particular to a multi-image hiding system which takes a diffractive optical element as a carrier and loads a plurality of secret information images encrypted by a visual password scheme.

Background

Visual cryptography is an encryption method based on the ability of human visual system to identify correlation and a random grid. The visual cryptography is an information encryption technology taking an image as a medium, the technology encodes an image carrying information into a plurality of shared images hiding the information through a special algorithm rule, and the information of an original image can be obtained by decrypting with human eyes as long as a specific number of sub-images are accurately aligned and superposed without depending on any relevant knowledge and calculation of cryptography. See (Eurocrypt 1994(1):1-12, 1994).

The visual password has better concealment, the secret information is concealed in a plurality of shared images, and meanwhile, the security of the encrypted information is ensured by a decryption mode with a threshold characteristic. However, the conventional decryption method of the visual password is single, and only the decryption method is printed on a transparent sheet or is performed in a computer in an overlapping way.

At present, related work aiming at the problem of single decryption method mainly uses an optical means as a carrier to load and share images and expand the application range of visual passwords. Taking a diffractive optical element as an example, one diffractive optical element loads one shared image, the shared image is reproduced through an optical means during decryption, and the shared image can be decrypted after superposition.

Disclosure of Invention

The invention aims to improve the information capacity of an image encryption hiding system based on a visual password. The invention adopts a proper algorithm to design the diffractive optical element, and loads a plurality of shared images into the same diffractive optical element to realize multi-image hiding. When decrypting, the diffraction optical element is irradiated by parallel light, different shared images can be reproduced at different distances behind the element, and the hidden secret information can be decrypted by aligning and overlapping the corresponding shared images.

The technical scheme of the invention can be divided into two parts, namely an encryption part and a decryption part, the technical scheme of the encryption part is as follows, and the flow chart is shown in figure 1:

(1) encrypting m pieces of secret information by using a visual cryptography scheme, wherein each piece of secret information can be coded into n shared images to obtain m × n shared images (A11, A12, A13, … …, Amn);

(2) dividing the shared images obtained in the step (1) into n groups, dispersing the shared images of each secret information in the n groups, sequencing the shared images in each group, and setting a diffraction distance;

(3) designing a diffraction optical element, wherein each group of shared images corresponds to one diffraction optical element, taking the shared images and the diffraction distance as parameters, and calculating by using a phase recovery algorithm to obtain the diffraction optical elements so as to obtain n diffraction optical elements in total.

The technical scheme of the decryption part is as follows, and the flow chart is shown in figure 2:

(1) finding out the positions of the images which need to be shared by the secret information needing to be decrypted in each group;

(2) irradiating each diffractive optical element with parallel light, and obtaining a required shared image at a specific position behind the element according to the data searched in the step (1);

(3) and aligning and superposing the shared images, and decrypting the secret information.

The shared images can be decrypted only by incoherent superposition during decryption, and as shown in fig. 3, the secret information can be decrypted after the two reproduced shared images are aligned and superposed, so that the decryption process is simple to operate, the methods are various, for example, a light path is established to align and superpose the reproduced images in space, then a white screen is used for receiving, an industrial camera can be used for receiving the diffraction images behind the diffraction element, and then the images are superposed and decrypted in a computer. The encryption scheme can also be modified somewhat according to the decryption method, such as grouping reduction, and shared images of the same secret information can be recorded in the same group by the same diffractive optical element, so that the information capacity can be further increased. Therefore, the specific encryption and decryption scheme needs to be selected according to actual requirements.

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

(1) compared with the traditional visual secret scheme taking an optical means as a carrier, the method has the advantages that a plurality of analysis images can be hidden in each diffractive optical element, and only one shared image can be hidden in the traditional method, so that the method has high information capacity;

(2) the concealment and the safety are further improved, the transparent diffractive optical element is used as a carrier, the concealment is good, the parameter of the diffraction distance is increased in the encryption process, the cracking difficulty is improved, and the safety is better;

(3) the decryption method is convenient and effective, a complex computer program or a complex and accurate light path is not needed, the decryption process only needs parallel light irradiation, the specific shared image is aligned and overlapped to be decrypted, the decryption can be recognized by naked eyes, and the decryption method is convenient and fast and is various.

Drawings

Fig. 1 is a flowchart of an image encryption process.

Fig. 2 is a flowchart of the decryption process.

Fig. 3 shows the reproduced shared image non-coherent superposition decryption.

Fig. 4 shows secret information in an embodiment.

Fig. 5 shows a shared image obtained by encrypting through a visual cryptography scheme.

Fig. 6 shows two diffractive optical elements hiding multiple shared images.

Fig. 7 is a reproduction of a shared image by a diffractive optical element.

Fig. 8 is a diagram illustrating the corresponding shared images after reproduction being aligned and superimposed to decrypt the secret information.

Detailed Description

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

The 4 images in fig. 4 are used as secret information.

The secret information is encrypted by using a visual password scheme, which has a plurality of coding schemes, and takes a simpler "(2, 2) -visual password scheme" as an example, so as to obtain 8 shared images, as shown in fig. 5.

The shared images were divided into two groups and arranged with diffraction distances of z1=200mm, z2=400mm, z3=600mm, and z4=800 mm.

The phase information of the two diffractive optical elements is calculated using the GS algorithm, as shown in fig. 6.

When the two diffractive optical elements are irradiated by parallel light during decryption, a plurality of shared images can be reproduced at the back as shown in fig. 7, and the corresponding shared images are aligned and superposed as shown in fig. 8, namely secret information.

The method and the example are a multi-image optical information hiding system based on visual passwords, secret information is encrypted through a visual password scheme, a plurality of shared images are hidden through a diffractive optical element, and multi-image encryption and hiding are achieved through an optical means. The specific embodiment of the present invention is not limited to the above embodiments, and parameters such as diffraction distance, number of images, size of images, etc. may be modified according to the requirement, and other visual cryptography schemes or phase recovery algorithms may also be selected.

Claims

1. A multi-image optical hiding system based on visual passwords is characterized in that a plurality of pieces of secret information are encoded by using a visual password scheme to obtain a shared image; sequencing a plurality of shared images, setting a distance parameter, and designing a diffraction optical element by using a phase recovery algorithm; and during decryption, different shared images are obtained by using parallel light incidence, and the corresponding shared images are aligned, superposed and decrypted.

2. The multi-image optical hiding system of claim 1, wherein the secret information is encoded using a visual cryptography scheme to obtain multiple shared images.

3. The multi-image optical hiding system of claim 1, wherein the diffractive optical element is designed using a phase recovery algorithm with the multi-shared image and distance parameters as constraints such that different shared images can be received at different distances behind the diffractive optical element after the parallel light illuminates the diffractive optical element.

4. The multi-image optical hiding system according to claim 1, wherein different shared images are obtained at different distances behind the parallel light illuminating element according to a distance parameter when the diffractive optical element is designed, and the shared images corresponding to the secret information to be decrypted are aligned and superimposed, so that decryption can be performed.