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A Review of Data Hiding in Images

Eugene T. Lin and Edward J. Delp

Kristin Burke 2

Overview

Introduction

Digital Steganography

Applications

Copyright Protection

Feature Tagging

Secret Communications

Data Hiding Techniques

Digital Embedding

Steganalysis

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Introduction

Steganography - hiding secret information

so that its existence is concealed

Used for hundreds of years

Example:

Im feeling really stuffy. Emilys medicine

wasnt strong enough without another

febrifuge.

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Digital Steganography

Terminology

Message

Data that the sender wishes to hide

Can be text, images, audio, video, etc.

Cover

Medium in which the message is embedded

Stego-image

The resulting image and the message combined

Stego-key (optional)

used to extract the message from the stego-image

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Digital Steganography

Recovering the message from the stego-

image requires:

stego-image

stego-key (if applicable)

(sometimes) original image

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Steganos

Specific LSB technique

Can imbed data in image, audio and text

covers

Digital Image Steganography: Data Sneaking Between the Pixels 14

24 bit image example:

24 bit images use 3 bytes to represent a color value (8 bits = 1 byte)

1 pixel = (00100111 11101001 11001000)

red green blue

Simplified Example with a 24 bit pixel:

1 pixel: (00100111 11101001 11001000)

Insert 101: (00100111 11101000 11001001)

red green blue

http://www.mills.edu/ACAD_INFO/MCS/CS/S02MCS125/Steganography.htm

LSB

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LSB Example- Step 1

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LSB Example - Step 2

The first least signifi cant bitplane of Arctic hare has been replaced with the f irst mostsignificant bitplane of F15: 64 KB hidden. Extracted to the right.

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LSB Example - Step 3

The 2 least significant bitplanes of Arctic hare have been replaced with the 2 mostsignificant bitplanes of F15: 129 KB hidden.

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LSB Example - Step 6

The 5 least significant bitplanes of Arctic hare have been replaced with the 5 mostsignificant bitplanes of F15: 323 KB hidden

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LSB Example - Step 7

The 7 least significant bitplanes of Arctic hare have been replaced with the 7 mostsignificant bitplanes of F15: 452 KB hidden.

http://www.cl.cam.ac.uk/~fapp2/steganography/image_downgrading/08.html

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Transform Embedding

Embedding the message by modulating thecoefficients in a transform domain

Discrete-Cosine Transformation (DCT) Discrete Courier Transform

Wavelet Transform

Offer superior robustness against lossycompression

Spread-spectrum techniques spread energyof message across frequency bands

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DCT

DCT or wavelettransform

f

Find

insignificant

coefficients

Insert

101110111011

110011010011

101101011101

100011011101

(message)

into coefficientsTake inverse

transform

f-1

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Perceptual Masking Systems

Exploit properties of the human visual

system

Masking - signal is imperceptible in the

presence of other signals (needle in a

haystack)

Perform analysis of image before

imbedding and place data in specific

regions

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Steganalysis

Practice of attacking steganographicmethods by detection, destruction,

extraction or modification of embedded data Success:

Finding message in secret communication

Finding & changing watermark in copyrightimages

Like cryptanalysis in that entire securitybased on stego-key

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Steganalysis

Techniques divided into categories:

stego-only

known cover known message

chosen stego

chosen message (most powerful)

Most difficult attacks:

Modifying the embedded message

Deducing the stego-key

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Review

Introduction

Digital Steganography

Applications

Data Hiding Techniques

Digital Embedding

Steganalysis

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Questions?