IMAGE SECRET SHARING

Presented by : Nikita KasarGuided by : Dr. Sonali Patil

INTRODUCTION

• Secret sharing is a technique for protecting sensitive data, such as cryptographic keys. • Secret sharing is used in modern

cryptography to lower the risks associated with compromised data. • The first secret sharing schemes were

proposed by Shamir and Blakley in 1979.

PROBLEM STATEMENT

To provide security to images using secret sharing algorithm.

OBJECTIVE

•To study different image secret sharing algorithms.

• To secure data transmission in networks which are used for exchange of private images.

MOTIVATION

• If we do not process or hide our secret information, the information might be stolen by the hackers easily.• The information is kept in a single

information-carrier. If the information-carrier is lost or destroyed by an attacker, the secret information might disappear.

WHY SECRET SHARING?

• Encryption – Single point failure.• Decryption key may be lost.• Encrypted content is corrupted during

transmission.

To address these reliability problems , an image secret sharing scheme is good alternative to remedy such vulnerabilities.

LITERATURE SURVEY

-------SHAMIR’S ALGORITHM------

• ● Based on polynomial interpolation • ● It's (k, n) threshold scheme • ● Dealer D distribute a secret s to n players • ● At least k participant's are required to

construct a secret s

THRESHOLD SCHEME

• Divide some data D into pieces/shadow images D1,D2,……Dn in such a way that :• i) Knowledge of any k or more Di pieces

makes D easily computable.• Ii)Knowledge of any k-1 or fewer Di pieces

leaves D completely undetermined(in the sense that all its possible values are equally likely.)

Secret sharing in images• Each pixel value of a secret image is a secret

message. • We use the secret image to generate shadow

images and only require part of these shadow images to reconstruct the secret image. • The shadow images should not reveal any

information about the image.• Ideally, each shadow image should look like

random noise so that anyone without the permission won’t be able to get any information about a secret image

Generation of Shadow images

. Image sharing algorithm (1) Suppress all pixels whose gray values greater than 250 to 250.(2) Permute the pixels of the secret image to get a permuted image, and pick up an integer threshold k. (3) Sequentially take k not-shared-yet pixels of the permuted image to form a (k-1)-degree polynomial. q(x)≡a0+a1x+a2x2+…+ak-1xk-1 mod 251 where a0, a1, …, ak-1 are the k pixel values we take. Then generate n pixel values q(r1),q(r2),…, q(rn) for n shadow images, where 1 <= r1 <r2 <rn <= 250. (4) Repeat step (3) until all pixels of the permuted image are obtained.

Shadow image acquisition

• The equation can be written byq(x)≡a0+a1x+a2x2+…+ak-1xk-1 mod 251

• Select n distinct secret keys x1,x2,…,xn.

• Deliver (xi,s(xi)) to the i th participant.

Revealing algorithm(1) Collect at least k shadow images. (2) Take the first unused pixel from each of k shadow images. (3) Use these k pixel values and Lagrange’s polynomial interpolation to solve for the coefficients a0, a1, …, ak-1. Put these coefficients into the permuted image sequentially.(4) Repeat steps (2) and (3) until all pixels of the k shadow images processed. (5) Inversely permute the pixels of the permuted image to recover the original secret image.

Recovery of secret

ADVANTAGES

• The Shamir’s secret sharing scheme has a good abstract foundation which provides an excellent framework for proofs and applications.• Shares can be easily added or removed without

affecting other shares.• It is easy to change shares , keeping the same

secret.• It is possible to provide more than 1 share per

individual.

DISADVANTAGE

• The Shamir-based method utilizes a scheme of Lagrange polynomial interpolation to recover the secret image from k out of n shadow image generated from an original secret image. • This method might expose some image features

in the shadow images without preprocessing the secret image.

APPLICATIONS

• Medical applications such as tele diagnosis require information exchange over insecure networks.

• Password generation using shares.

• Generating shares by director of bank for the bank’s vault unlocking code

APPLICATIONS

• ● Key Escrow/ Key Backup• ● Used to build other cryptographic primitives • ● Secure multi party computation• ● Electronic voting system

CONCLUSION & FUTURE SCOPE

- Share highly sensitive information- Secret cannot be revealed with (k-1) shares- Secure storage-Use of Watermarking &Steganography

REFERENCES• A. Shamir, “How to share a secret,” Communications of the

ACM, Vol. 22, No.11, 612613, 1979. • C.C. Thien and J.C. Lin, “Secret image sharing,” Computer &

Graphics, Vol.26, No.1, 765-7710, 2002.• “An Image Secret Sharing Method”,Li Bai Saroj Biswas ECE

Department Temple University Philadelphia, PA, U.S.A. lbai@temple.edu

• A STUDY ON SECRET IMAGE SHARING Ming-Hong Tsai1 and Chaur-Chin Chen2 1,2Department of Computer Science, National Tsing Hua University, Hsinchu 30013, Taiwan 2Institute of Information Systems & Applications, National Tsing Hua University, Hsinchu, Taiwan