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steganography Jaykrishna thakkar Natubhai.v.patel College of pure and applied science
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Page 1: Steganography

steganography

Jaykrishna thakkar

Natubhai.v.patel College

of pure and applied science

Page 2: Steganography

outline

Introduction History Types Technique

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introduction The word steganography is derived from two Greek

words stegos meaning cover and grafia meaning writing, defining it as covered writing.

In image steganography the information is hidden exclusively in image.

Steganography is an art and science of secret communication.

It is the practice of encoding/embedding secret information in a manner such that the existence of the information is invisible

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introduction

After inserting the secret message it is referred to as stego-medium.

A stego-key is used for hiding/encoding process to restrict detection or extraction of the embedded data.

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history (past)

Ancient origins can be traced back to 440 BC. Although the term steganography was only coined at

the end of the 15th century, the use of steganography dates back several millennia.

In ancient times, messages were hidden on the back of wax writing tables, written on the stomachs of rabbits, or tattooed on the scalp of slaves.

Invisible ink has been in use form centuries for fun by children and students and for serious undercover work by spies and terrorists

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present

The majority of today's steganographic systems uses multimedia objects like image, audio, video etc as cover media because people often transmit digital pictures over email and other Internet communication.

Modern steganography uses the opportunity of hiding information into digital multimedia files and also at the network packet level

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Types of steganography

FragileRobust

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fragile

Fragile steganography involves embedding information into a file which is destroyed if the file is modified. This method is unsuitable for recording the copyright holder of the file since it can be so easily removed, but is useful in situations where it is important to prove that the file has not been tampered with, such as using a file as evidence in a court of law, since any tampering would have removed the watermark. Fragile steganography techniques tend to be easier to implement than robust methods.

Fragile steganography involves embedding information into a file which is destroyed if the file is modified. This method is unsuitable for recording the copyright holder of the file since it can be so easily removed, but is useful in situations where it is important to prove that the file has not been tampered with, such as using a file as evidence in a court of law, since any tampering would have removed the watermark. Fragile steganography techniques tend to be easier to implement than robust methods.

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robust

Robust marking aims to embed information into a file which cannot easily be destroyed. Although no mark is truly indestructible, a system can be considered robust if the amount of changes required to remove the mark would render the file useless. Therefore the mark should be hidden in a part of the file where its removal would be easily perceived.

There are two main types of robust marking. Fingerprinting involves hiding a unique identifier for the customer who originally acquired the file and therefore is allowed to use it. Should the file be found in the possession of somebody else,

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robust (continue)

the copyright owner can use the fingerprint to identify which customer violated the license agreement by distributing a copy of the file.

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techniques of steganography

Least Significant Beat (LSB)

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Least significant bit (Lsb)

The least significant bit (in other words, the 8th bit) of some or all of the bytes inside an image is changed to a bit of the secret message.

Digital images are mainly of two types (i) 24 bit images and (ii) 8 bit images.

In 24 bit images we can embed three bits of information in each pixel, one in each LSB position of the three eight bit values.

Increasing or decreasing the value by changing the LSB does not change the appearance of the image; much so the resultant stego image looks almost same as the cover image.

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LSB - Example For example, suppose one can hide a message in

three pixels of an image (24-bit color). Suppose the original 3 pixels are

(11101010 11101000 11001011)(01100110 11001010 11101000)(11001001 00100101 11101001)

(11101010 11101001 11001010)(01100110 11001011 11101000)(11001001 00100100 11101001)

A steganographic program could hide the letter "J" which has a position 74 into ASCII character set and have a binary representation "01001010", by altering thechannel bits of pixels.

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exampLe (continue)

In this case, only four bits needed to be changed to insert the character successfully.

The resulting changes that are made to the least significant bits are too small to be recognised by the human eye, so the message is effectively hidden.

Best to use a grayscale palette or one with gradual changes in shades

Otherwise, it is best to use images with “noisy areas” – areas with ample color variation and without large areas of solid color

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grey scaLe

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nebuLa

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“noisy areas” - exampLe

renoir painting

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LSB - USeS

Storing passwords and/or other confidential information

Covert communication of sensitive data

Speculated uses in terrorist activities Being widely used to hide and/or transfer

illegal content

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RefeRence

1). R.Anderson and F. Petitcolas, "On the limits of steganography" IEEE Journal of Selected Areas in Communications, Vol. 16, No. 4, May 1998.

Information Hiding Techniques for Steganography and Digital Watermarking

By:-Stefan Katzenbeisser & Fabien A. P. Petitcolas

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Any qUeStion’S

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