Grey Level Modification Steganography2

8/3/2019 Grey Level Modification Steganography2

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Techniques

Common approaches include:

LSB insertion

Masking and filtering

Algorithms and transformations

Image Steganography



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LSB insertion

Simplest approach

LSBs of bytes of cover image replaced withmessage bits

Techniques

Cover image

Message to be

embedded

Encryption

(optional)

MSB

LSB

Stego imageKey



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LSB insertion

Example:

Hiding letter A in an image

Binary code for A is 10000011

Assume 3 pixels of raster data

(00100111 11101001 11001000)

(00100111 11001000 11101001)

(11001000 00100111 11101001)

Replace each LSB with bit of A

Techniques



4

LSB insertion

Example:

Hiding letter A in an image

Binary code for A is 10000011

New raster data is

(00100111 11101000 11001000)

(00100110 11001000 11101000)

(11001001 00100111 11101001)

Techniques



5

DCT manipulation

Data is inserted during JPEG compressionprocess

First we divide image into 8 x 8 blocks of pixels

Techniques



6

DCT manipulation


Now we take the 64 (8 x 8) pixel values f(x,y) and calculate their DCT coefficients F(u,v)

Next step is quantization

Techniques



7

DCT manipulation


Data is placed in the LSBs of the quantized DCTcoefficients

Techniques

DCT coefficients

Message to be

embedded

Encryption

(optional)

MSB

LSB

Modified

coefficients

Key



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Basic concepts…

Uncompressed audio files containredundant information

Human Auditory System has some limitations

This is exploited by compression algorithms

like MP3

Such compression algorithms can bemodified to spare some redundant portions

and then embed data in them

Audio Steganography



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Techniques

Some methods are:

Low-bit encoding

Phase encoding

Spread-spectrum encoding

Echo data hiding

Audio Steganography



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Low-bit encoding

Audio version of LSB insertion

Message bits embedded in LSBs of audiosamples

Embedding may straight or random

Audio Steganography



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Phase encoding

Message bit is represented by two valuesof phase

Audio sample is broken into small segments

Audio Steganography



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Phase encoding

Message bit value (0/1) is represented bytwo values of phase

Initial phase of each segment is changed toone of the two reference values

Phases of remaining samples are also changedto maintain phase relationships

Audio Steganography

Change phase of 1st sampleaccording to message bit



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Spread spectrum

Same as for images

Message is OR-ed with PN sequence and addedto audio sample LSBs or LSBs of their FFT coefficients

Audio Steganography



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Echo data hiding

Message is ‘hidden’ in the time delaybetween sounds and their echos

By having two values of echo delay, we canencode 0s and 1s

For small values of echo delay, human ear doesnot perceive echo as distortion

Audio Steganography



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What is it?

Digital watermarks are embedded in audioor visual media primarily to protectcopyrights

Watermarks may be visible or invisible

E.g. Channel logo on the TV screen

They must be robust against destructivemanipulation

Capacity is not an issue here, nor is secrecy

Digital Watermarking



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Steganography vs. Watermarking

Differences

Steganography is a

means of covertcommunication

It must be ‘invisible’ toa third party

Cover capacity isimportant

Watermarking is used

to protect authorshipof digital media

Watermarks may ormay not be invisible

Cover capacity is notimportant, as messagesize is small



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Public domain software

S-Tools

Invisible Secrets

White Noise Storm

MP3Stego Many more…

Steganography Tools



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Types

Passive

Involves detecting the presence of a hiddenmessage and guessing the algorithm used

Active

Involves attempting to extract or modify themessage

Steganalysis



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Data erasure

Audio

Replacing LSBs with random data

Resampling

Echo cancellation

Steganalysis



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Where has Steganography found use?

Governments, law enforcement agencies

Covert communication

Media companies

Digital watermarking

Medical institutions

Matching patients’ records and images

Corporations and individuals

Applications



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Some cases of misuse…

Extensive use of steganography by al-Qaeda terrorists to exchange information

Revealed by CIA after 9/11

Cases reported of corporate employees

using steganography to leak out sensitivedata

Some anti-social groups using it for covert

communication

Applications



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On the future of Steganography…

Steganography has advanced greatly since

the advent of computers, and will continueto do so

Steganography can be very successful,

provided the proper mechanisms arechosen

Future lies in ‘on-the-fly’ steganography

Concluding Remarks



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On the future of Steganography…

Governments are investing heavy sums in

developing powerful Steganalysis tools todeal with hazards of unchecked data flow

Restrictions on development or export of

steganography will only provecounterproductive

Concluding Remarks



Outline

Steganography history

Steganography and Steganalysis

Security and capacity Targeted steganalysis techniques

Universal steganalysis

Next generation practical steganography Conclusion



Cover Media

Many options in modern communication system: Text Slack space Alternative Data Streams

TCP/IP headers Etc.

Perhaps most attractive are multimedia objects - Images Audio Video

We focus on Images as cover media. Though mostideas apply to video and audio as well.



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Grey Level Modification Steganography2

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