message concealment using steganography

MESSAGE CONCEALMENT

USINGSTEGANOGRAPHY

Guided By:- Presented By:Ms. Sumeet Kaur Sukhpreet KaurLecturer M.Tech (Part Time) Deptt.of CE 5th SemYadavindra College of Engg. 07MCP013

• Steganography is the art of hiding the fact that communication is taking place, by hiding information in other information.

• . Many different carrier file formats can be used, but digital images are the most popular because of their frequency on the Internet.

• There exists a large variety of steganographic techniques some are more complex than others and all of them have respective strong and weak points .

• In this report I have studied a different types of algorithms available for image steganography and a comparison of them is prepared.

• I have proposed one LSB based technique as future work

Overview

Introduction to SteganographyDifferent types of SteganographyTechniques of Image SteganographyDiscussion and Analysis of Existing

TechniquesConclusion & Future Work

• Steganography is the art and science of writing hidden messages .

• The word "Steganography" is of Greek origin and means "covered, or hidden writing". Its ancient origins can be traced back to 440 BC.

• This is in contrast to cryptography, where the existence of the message itself is not disguised, but the content is obscured.

Steganography has been widely used in historical times, especially before cryptographic systems were developed. Examples of historical usage include:

• Wax tablets.• Secret inks.• Microdots.• Cipher texts.

In modern approach, depending on the nature of cover object, Steganography can be divided into five types:

Text Steganography Image Steganography Audio/Video Steganography Protocol Steganography

Text Steganography

Line-shift encoding Word-shift encoding Feature specific encoding:

Image Steganography

Image DomainTransform Domain

Audio Steganography

Low-bit Encoding Phase coding Spread spectrum

Protocol SteganographyThe term protocol steganography

refers to the technique of embedding information within messages and network control protocols used in network transmission

To hide information, straight message insertion may encode every bit of information in the image or selectively embed the message in “noisy” areas that draw less attention—those areas where there is a great deal of natural color variation. The message may also be scattered randomly throughout the image.

Image Domain Techniques

Least significant bit insertion LSB in GIF Patchwork

Transform Domain

JPEG Steganography

The LSB of a byte is replaced with an M’s bit.Works well for image, audio and video

SteganographySuppose we want to encode letter A (having ASCII

value 10000001)in the following raster data for 3 pixels(9 bytes)

(00100111 11101001 11001000)(00100111 11001000 11101001)(11001000 00100111 11101001)

It becomes(00100111 11101000 11001000)(00100110 11001000 11101000)(11001000 00100111 11101001)

Only three bits needs to be changed actually.On average, LSB requires that only half the bits in an

image be changed.

Fig. 1: The cover image

Fig. 2: The stego-image (after A is inserted)

•GIF are palette based images•Each pixel is represented as a single byte and the pixel data is an index to the colour palette .•The colors of the palette are typically ordered from the most used colour to the least used colors to reduce lookup time •one change in the least significant bit of a pixel, it can result in a completely different colour since the index to the colour palette is changed.•One solution is to use Grayscale images

LSB in GIF

Patchwork

This algorithm randomly selects pairs of pixels on a given image.The brighter of the two pixels is made brighter, and the darker one darker.The contrast change between these two pixels now forms part of the bit pattern for the hidden file.

Transform Domain

Transform domain techniques[13] hide data in mathematical functions that are in compression algorithms. Discrete Cosine Transform (DCT ) technique is one of the commonly used transform domain algorithm for expressing a waveform as a weighted sum of cosines.

Transform Domain Contd..

The DCT transforms a signal from an image representation into a frequency representation, by grouping the pixels into 8 × 8 pixel blocks and transforming the pixel blocks into 64 DCT coefficients each.Embedding of data is done by altering the DCT coefficients.

Following criteria has been proposed for imperceptibility of an algorithm:

Invisibility Payload capacity Robustness against statistical attacks Robustness against image manipulation Independent of file format Unsuspicious files

The levels at which the algorithms satisfy the requirements are defined as high, medium and low.

High:-means that the algorithm completely satisfies the requirement

Low:-low level indicates hat the algorithm has a weakness in this requirement.

Medium:-medium level indicates that the requirement depends on outside influences

LSB is the most popular and straight forward technique for image Steganography but it is also most vulnerable to attacks.

It is used when secret amount of information is more.

LSB in GIF can store less data than BMP. Also minor change in palette is visible.

It is efficient when used with grey scale images to store small amount of data.

Patchwork technique embed data repeatedly in image so it is robust against image manipulation.

Its problem is small capacity. It is suitable for small amount of sensitive

information.JPEG compression is very secure method as stego

image’s secret data is not visible to attacker.It is very mathematical process and difficult to

implement. it is used to send secret images over internet.

ComparisonTechnique

Parameter

LSB in BMP

LSB in GIF

Jpeg Compression

Patchwork

Invisibility High* Medium*

High High

Capacity High Medium

Medium Low

Robustness Against Statistical Attacks

Low Low Medium High

Robustness against image

Manipulation

Low Low Medium High

Independent of file format

Low Low Low High

Unsuspicious files

Low Low High High

There exists a large selection of approaches to hiding information in images. All the major image file formats have different methods of hiding messages, with different strong and weak points respectively.

Where one technique lacks in payload capacity, the other lacks in robustness. Like LSB has high capacity and patchwork has more security.

Algorithm chosen depend upon application.

Future WorkTo design LSB Based TechniqueThat provide more capacity by using 4-LSB

method.To increase security encryption will be done

before hiding data.To use only a subset of pixels for increasing

invisibility.Proper cover selection will be done to make

file look unsuspicious.

Outline of algorithmSelect proper cover and convert it into binary form.Convert secret message into ASCII format and then in

binary equivalent.Encrypt message using some encryption algorithm.Take first byte of message and insert it into first byte

of image after image header as 4-LSB.Take second byte of data and insert it in the second

byte of image as 4- LSB. Then leave next 4 bytes.Then insert next character in image.Convert image again to image format and send.At receiver side just reverse the process.

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Thanks