Crypto Ppt 3semi 4

ASeminar on the topic

VISUAL CRYPTOGRAPHY ON IMAGES

Presented by Presented by Miss. Archana B. DholeMiss. Archana B. DholeM.Tech. IIIrd Sem.(CSE) M.Tech. IIIrd Sem.(CSE) R.C.E.R.T. Chandrapur R.C.E.R.T. Chandrapur

Contents

Introduction to Visual Cryptography.

Background Literature Survey Research Component Conclusion References

Introduction to Visual Cryptography With the rapid advancement of network technology,

multimedia information is transmitted over the Internet conveniently.

Various confidential data such as military maps and commercial identifications are transmitted over the Internet.

While using secret images,security issues should be taken into consideration because hackers may utilize weak link over communication network to steal information that they want .

To deal with the security problems of secret images, various image secret sharing schemes have been developed.

Visual cryptography is introduced by first in 1994 Noar and Shamir

Introduction to Visual Cryptography Visual Cryptography is a special type of

encryption technique to obscure image-based secret information which can be decrypted by Human Visual System (HVS).

This cryptographic system encrypts the secret image by dividing it into n number of shares and decryption is done by superimposing a certain number of shares(k) or more.

Simple visual cryptography is insecure because of the decryption process done by human visual system.

Background Visual Cryptography is proposed by Moni Naor

and Adi Shamir in 1994. Modifications done for extension to Gray and

Color Images. Naor and Shamir have developed the Visual

Secret Sharing Scheme(VSSS) to implement this model on binary images.

In k out of n VSSS(which is also called (k, n) scheme), an binary image(picture or text) is transformed into n sheets of transparencies of random images.

The original image becomes visible when any k sheets of the n transparencies are put together, but any combination of less than k sheets cannot reveal the original binary image.

In the (2, 2) VC scheme each secret image is divided into two shares such that no information can be reconstructed from any single share. Each share is printed in transparencies.

In the above basic VC scheme each pixel ‘p’ of the secret image is encrypted into a pair of sub pixels in each of the two shares. Therefore when stacking two tranparencies, the block corres. to black in the secrete image is full black. And those for white pixels are half black and half white.

1. Basic Model The basic model of visual cryptography proposed by Naor and Shamir accepts binary image ‘I’ as secret image, which

is divided into ‘n’ number of shares. Each pixel of image ‘I’ is represented

by ‘m’ sub pixels in each of the ‘n’ shared images.

The resulting structure of each shared image is described by Boolean matrix ‘S’

Where S=[Sij] an [n x m] matrix Sij=1 if the jth sub pixel in the ith

share is black Sij=0 if the jth sub pixel in the ith

share is white

Permutation

Figures

Original image b) Encrypted image c) Decrypted imageFigure 2: Encryption and Decryption process

Literature Survey

• According to an overview of Visual Cryptography

• In the (2,2) VC scheme each secret image is divided into two shares such that no information can be reconstructed from any single share.

• Visualized In order to hide secrecy we go for expansion and increasing of the number of shares but this affects the resolution.

Cont.

•Therefore an optimum number of shares are required to hide the secrecy.• At same time security is also an important issue. •In this paper VC schemes for gray level, Recursive Threshold visual Cryptography, Extended visual Cryptography for natural images are defined.

According to Error Filtering Schemes for Colour Images in Visual Cryptography

• Two Basics ideas used are error diffusion and pixel synchronization.

• Error diffusion is a simple but efficient algorithm for image halftone generation

• The quantization error at each pixel level is filtered and fed as input to the next pixel.

• Low frequency that is obtained between the input and output image is minimized which in turn gives quality images.

According to Visual Cryptography for color images

Rijmen and Preneel have proposed a visual cryptography approach for color images.

This paper proposes three methods Visual cryptography of gray level and

color images based on past studies in black and white visual cryptography

The halftone technology and The color decomposition method.

Halftone Images

Fig. 4. (a) Continuous tone, and (b) Halftone

Colour Decomposition

Additive Model Substractive Model

RB

G

C Y

M

Cyan

Magenta

According to the visual cryptographic technique to secure Image shares by Jagdeep Verma

Visual Cryptography is a method of encrypting a secret image into shares such that stacking a sufficient number of shares is shares reveals the secrete image.

Shares are binary images usually presented in transpariencies.

3 out of 3 visual cryptography

0011 1100 0101 1010 01101001

horizontal shares vertical shares diagonal shares

•The secret shares generated from VC encryption are watermarked into some host images using digital watermarking.•Digital watermarking is used for providing the double security of image shares.•The share is embedded into the host image in frequency domain using Discrete Cosine Transform (DCT).

• The process of watermark extraction necessitates only the watermarked image and it does not require the original host image.• The scheme provides more secure and meaningful secret shares that are robust against a number of attacks like blurring, sharpening, motion blurring etc.

Structure of proposed scheme & Experimentation result

According to Visual Cryptography Scheme for Color Image using Random Number with Enveloping by Digital Watermarking paper presented by Kandar, Maiti & Dhara

As pixels is a smallest unit, each pixel of a 32 bit digital color image are divided into four parts namely Alpha, Red, Green and Blue each with 8 bits.

Alpha bit represents degree of transparency.11100111 11011001 11111101 00111110 Alpha Red Green Blue Fig 1: Structure of a 32 bit pixel Human visual system acts as an OR function. Proposed tech. digital enveloping is used.

According to the Visual cryptography for color images by Young Chang Hou

Proposed methods for black and white images, gray level and color images.

In their approach each pixel of the color secret image is expanded into a 2x2 block to form two sharing images

Each 2x2 block on the sharing image is filled with red, green, blue and white.

Research Component Our research is the implementation of

algorithms on visual cryptography in images. The future work is to improve the contrast

and reduce the pixel expansion in the resultant secret image.

Further extend this work to use this technique with color images. Also consider 3D images for creating the shares that have partial secret and reveal that secret by stacking to each other.

Conclusion Visual cryptography is the current area of

research where lot of scope exists. Currently this particular cryptographic

technique is being used by several countries for secretly transfer of hand written documents, financial documents, text images, internet voting etc.

There are various innovative ideas and extensions exist for the basic visual cryptographic model introduced till now.

One such enhancement we are trying to do. In the existing VC schemes no security is provided to the secret shares.

References Jagdeep Verma, Dr.Vineeta Khemchandani / International Journal of

Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 1,Jan-Feb 2012, pp.1121-1125

IJCSI International Journal of Computer Science Issues, Vol. 8, Issue 3, No. 1, May 2011 Visual Cryptography Scheme for Color Image Using Random Number with Enveloping by Digital Watermarking.

Visual cryptography for color images BY Young-Chang Hou∗ Department of Information Management, National Central University, Jung Li,

Taiwan 320, ROC Received 6 June 2002; accepted 26 August 2002. An overview of visual cryptography By Chandramati S., Ramesh Kumar R. ,

Suresh R. and Harish S.

www.dia.unisa.it/VISUAL/ www.cacr.math.uwaterloo.ca/~dstinson/visual.html www.leemon.com/crypto/visualCrypto.html

THANK YOU

System

InputOutput

Stack togather

Visual cryptography is a cryptographic technique which allows visual information (e.g. printed text, handwritten notes and pictures) to be encrypted in such a way that the decryption can be performed by the human visual system, without the aid of computers.

Visual cryptography scheme eliminates complex computation problem in decryption process, and the secret images can be restored by stacking operation.

This property makes visual cryptography especially useful for the low computation load requirement.