Extended Embedded Visual Cryptography Schemes

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UNDER THE GUIDANCE OFMRS. PUSHPA MOHAN

BY:

MD . A D NA N A HMA D 1HK 07CS041R ID D HIPR A TIM MITR A 1HK 07CS069

NA SIR U D D IN A HME D 1HK 08CS05 2

Embedded Extended Visual

Cryptography Schemes

10-05-2013CSE@HKBKCE


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Motivation

In cryptography, encryption and decryption of text messages uses different

types of cryptographic algorithms like RSA , Diffie Hellman, Hash

algorithms.

These algorithms are time-consuming.

Our idea is to secure the messages from the third party following the processof encryption and decryption with low complexity and computational process.

Our project is based on image cryptography (visual cryptography). In this no

such kind of algorithms are used.

In visual cryptography the transparencies are used to avoid the text from third

party . Usually after decryption the image quality gets reduced and the size of the

image is double the actual image. Our main focus is to improve the image

quality and the size of the image.



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Introduction



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Generation Of Transparencies

Each white pixel in the original logo is split into two same size blocks that havehalf black and white pixels.

When these two blocks are overlaid, they align exactly, so the result is a light-colored block (with half black and half white pixels).

When these two blocks are overlaid, the result is completely black block.

The decryption of images depends on the shares(trasparencies). But it reconstructsthe images with some losses in contrast and width of the images.

In 2 out of 2 cryptography scheme, secret gray scale image is encoded. Each pixel(p) of secret image (SI) can be split into two sub-pixels in each share. If one of the

pixel (p) is white, adjacent pixel is black. Each pixel has 50% probability of thegray scale colors.



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Generation Of Transparencies

Each pixel of the image is divided into smaller blocks. There are always thesame number of white (transparent) and black blocks.

If a pixel is divided into two parts, there are one white and one black block. If

the pixel is divided into four equal parts, there are two white and two blackblocks.

If the pixels of layer 1 and 2 are inverted or opposite, the overlaid version willbe completely black. This is an information pixel.

Binary values -1 is black and 0 is white.



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Sharing Of

Pixels

White pixels contains

no data whereas theblack pixels containsthe data.



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HALFTONE VISUAL CRYPTOGRAPHY

Sharing of images uses two basic principles. They are blue noise dithering and

void and cluster algorithm.

Let P = {1,2,.n} be a set of elements called participants, a visual

cryptography scheme for a setPofnparticipants.

Each participant inPreceives one share. Let 2Pdenote the set of all subsets of

P and let GQualified= 2P and GForbidden = 2P, where GQualified

GForbidden = .

The void and cluster algorithm uses a filter to determine the locations of voids

and clusters in the halftone images.

The halftoning technique is used to convert the grey-scale image to binaryimage.

In halftone VC, the original image for each share is divided into cells of size

Q1Q2.

The secret image is clearly generated but the relative contrast of the image will

have 1/16th

loss as compared to the original image. 10-05-2013CSE@HKBKCE


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Base Paper

Algorithm

HalftoningProcess

Input: The c x d dithering matrix D and a pixelwith gray-level g in input image I.

Output: The halftoned pattern at the position of

the pixel

For i=0 to c-1 do

For j=0 to d-1 to do

If g


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Base Paper

Algorithm

EmbeddingProcess



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Proposed Method

In halftone reconstruction, the quality of the image gets reduced proportionally to the

width of the image. Image quality depends upon the halftone cell size q.

In our project, we are going to use compression and filters to improve the quality of the

image.

LZW data compression algorithm is a powerful technique for lossless data compression

that gives high compression efficiency for images.

Lossless compression reduces the number of secret information pixels, which have to

be distributed homogenously in halftone shares and increases the quality of halftoneshares as well as reconstructed image and computing the complexity is also reduced.

The process for compressing the gray scale image is done using the method of Error

diffusion method.



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Proposed Method

The method used to implement is as per the following process:

1. Select the grey-scale image.

2. Apply the LZW compression technique for the grey-scale image.

3. Prepare the dictionary for the gray scale images.

4. In dictionary replace strings of characters with a Single code.5. Calculations are done by applying dynamic Huffman coding.

6. In compression of grey-scale image select the secret Information pixels.

7. Then generate halftone shares using error diffusion Method.

8. Filter process is applied for the output grey-scale image.

Filters are used to improve the quality of reconstructed image to minimize

the noises for sharpening the input secret image.



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Visual Cryptography using Error Diffusion

To produce halftone shares that carry significant visual information, Zhou and Arce

recently developed halftone visual cryptography (HVC) based on the principle of void

and cluster dithering.

Compared with EVC, the image quality of the shares is greatly improved and the

reconstructed image contains much less cross interference from the shares.

The void and cluster algorithm is used to choose the pixels, that are to be modified may

make the positions of the modified pixels dependent on the original halftone image.

In this HVC method, pixels that carry the secret image information are predeterminedbefore a halftone share is generated.

Error diffusion is simple and widely used. Halftone methods improve the image quality

and reduce the computational complexity.



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Modules Used

Interface design using Applet frame work

Visual cryptography implementation

Encoding

Decoding

Creating Transparencies

Un-hiding Image from Transparency

Testing and integration



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Conclusion

The image quality depends on the halftone cell.

Compression technique is used for lossless image quality and information. LZW

method uses of technique that is dictionary based compression algorithm.

The selection of minimum number of secret information pixels and non

information pixels then becomes easier for the generation of halftone and shares.

The quality of image is quite high as compared to the other techniques, security

analysis is also little high. The computational complexity is minimized.

In visual cryptography, the supported image formats are .PNG, .GIF and .JPEG.

Visual cryptography is used in bank application, election voting etc.



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Work Done And Work To Be Done

Work done so far :-

1. Designing of low level and high level design.

Work to be done :-

1. Implementation of all the remaining modules.

2. Testing and integration.



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Reference

Feng Liu and Chuankun Wu , Embedded Extended Visual Cryptography

Schemes , IEEE Transactionson information forensics and security, Vol.6, No.

2, June 2011.



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THANK YOU


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Extended Embedded Visual Cryptography Schemes