Steganography - SEMINAR

1. Introduction

        The aim of the steganography is to hide information in undetectable way in an video/image/audio file. Since the rise of internet one of the most important factors of information and communication has been security of information. Cryptography was created as a technique for secrecy of communication and many different methods have been developed to encrypt and decrypt data in order to keep message secret Unfortunately It sometimes not enough to keep contents of  message secret, it may also be necessary to keep existence of message secret. Hence in order to keep secrets secret a technique called steganography is used.


2. History of Steganography

 

Greek Words:

STEGANOS – “Covered”

GRAPHIE – “Writing

Thousands of years ago, the Greeks used steganography to hide information

Ø     One hiding method was to engrave a message in a block of wood, then cover it with wax, so it looked like a blank wax tablet.

When they wanted to retrieve the message, they would simply melt off the wax.


3. Steganography system

 

          Steganography is the art and science of writing hidden messages in such a way that no one apart from the intended recipient knows of the existence of the message; this is in contrast to cryptography, where the existence of the message itself is not disguised, but the content is obscured.

          The word "Steganography" is of Greek origin and means, "covered, or hidden writing".

 


Figure 2.2 A generic Steganography System

 

          Fig. 2.2 shows the block diagram of a secure steganographic system. Input messages can be images, texts, video, etc.

 



The components of steganographic system are:

§        Emb: The message to be embedded.

§        Cover: The data in which emb will be embedded.

§        Stego: A modified version of cover that contains the embedded message emb.

§        Key: Additional secret data that is needed for the embedding and extracting processes and must be known to both, the sender and the recipient.

§        fE: A steganographic function that has cover, emb and key as parameters and produces stego as output.

§        FE-1: A steganographic function that has stego and key as parameters and produces emb as output. FE-1 is the inverse function of fE in the sense that the result of the extracting process fE-1 is identical to the input E of the embedding process fE

 

          The embedding process fE embeds the secret message E in the cover data C. The exact position (S) where E will be embedded is dependence on the key K. The result of the embedding function is slightly modified version of C: the stego data C’. After the recipient has received C’ he starts the extracting process fE-1 with the stego data C’ and the key K as parameters.

          If the key that is supplied by the recipient is the same as the key used by the sender to embed the secret message and if the stego data the recipient uses as input is the same data the sender has produces (i.e., it has not been  modified by an adversary), then the extracting function will produce the original secret message E.

 

 

Difference between Steganography and Encryption

Ø      Encryption scrambles a message so it cannot be understood.

Ø      Steganography hides the message so it cannot be seen.

Ø      A message in “cipher text” for instance might arouse suspicion on the part of the recipient while an “invisible” message created with steganographic methods will not.

 

 

4. Comparison between Steganography, Cryptography and Digital Signatures

 

 

Cryptography

Greek Words 

     CRYPTO– Secret

     GRAPHY – Writing

Ø     Cryptography is transforming information into an unreadable format without any intermediary being able to dechiper it.

Ø     It is used to protect information such as credit card information, email messages, etc.

Ø     Input msg is called plaintext is encrypted wit a secret key. The enrypted msg is called chipertext

Ø     Cryptanalysis is the code breaking method

 

 

Digital signatures

Two different techniques are used for signing an object.

 

Ø     With the first method the sender attaches message digest to the original message and the signed message obtained is transmitted through the communication environment. The receiver recalculates the digest and compares it to the one received.

 

Ø     With the second method the two parties use public-key algorithms. Public-key algorithms use a pair of keys for each party involved in the communication:

Ø     a secret key, known only to the owner, and a public key, known to everybody. The sender encrypts the document using his secret key and sends it to the receiver, which decrypts the message using the public key of the sender. In both alternatives, if the decryption process is successful then the message is authentic.


5. LSB ALGORITHM FOR DATA HIDING

 

 

            We can also perform steganography using a computer. Everything in a computer is stored as 1’s and 0’s (a bit).


 

            Bits are grouped in sets of eight, one set is called a byte. One byte can be used to represent each letter of the alphabet.  This is what is used in text files.

01000001 = A

01000010 = B

01000011 = C

Ø      An image is an array of numbers that represent light intensities at various points (pixels).

Ø      Images can have 8 bits per pixel or 24 bits per pixel.

Ø      With 8 bits/pixel, there are 28, or 256, color varieties.

Ø       With 24 bits/pixel there are 224 , or 16,777,216, color varieties.

Ø       Color variation for a pixel is derived from 3 primary colors: red, green, and blue. 

24 bit image example:

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


            Each byte is interpreted as a number, which is how much of that colour is used to make the final colour of the pixel.

 

            The difference between two colours that differ by one in either one red, green or blue value is impossible to see with the human eye.


            If we change the least significant (last) bit in a byte, we either add or subtract one from the value it represents.

 

            This means we can overwrite the last bit in a byte without affecting the color it appears to be.

 

            We can use images to hide things if we replace the last bit of every colour’s byte with a bit from the message.



6. Applications of steganography.

 

  1. Digital rights management

      Storing important information like Bank account number, Password

 

2.  Copyright protection

      Watermark embedded in protected items can be used to trace the source of illegal copies

 

3. Confidential communication and secret  data storing

      Steganography provides potential capability to hide existence of Confidential data Strengthening the secrecy of encrypted data.

 

 

7. Steganalysis

 

         

            Steganalysis is the art of detecting the message's existence and blockading the covert communication. The goal of steganalysis tools is to automatically detect the existence of secret messages in media. Johnson and Jajodia pointed out that several steganographic tools would generate some dependent patterns in the stego-images. By extracting these specific patterns, a steganalyst can break the steganographic system. In order to define attack techniques used for steganalysis, five levels of attacks on steganographic system are introduced, i.e. stego-only, known cover, known message, chosen stego and chosen message attack.

 

Visual Analysis

          It tries to reveal the presence of secret communication through inspection, either with the naked eye or with the assistance of a computer.

 

Statistical (Algorithmic)Analysis –

            Reveals tiny alterations in an image's statistical behavior caused by steganographic embedding.

 

            The nominally universal methods developed to detect embedded stego-data are generally less effective than the steganalytic methods aimed at specific types of embedding.

 

            Digital signatures are used as a proof of authorship of the contents of a document.

8. Advantages of Steganography

 

 

Very simple: Steganography is very simple which just requires image, audio or video file to hide message.

 

Fast:  It is possible to hide and extract message within a short period of time.

 

Not able to detect embedded text easily

 

            It ensures “Integrity Protection” which makes sure that information has not been tampered with as it moves between source and destination

 

            It ensures “Authentication Validation” which verifies originator identificationide

 

            It is possible to hide “Copyright Information” such as ID of author and date of creation

 

 

Disadvantages of steganography

 

 

Easy to detect embedded text using steganalysis.

 

Used in only one-one communication.

 

Steganography can also be used for illegal purposes:

 

Concealing a plan for terroristic threats

  • It is believed that al-Qaeda used steganographic software to communicate plans with each other before the 9-11 attacks, this has not yet been confirmed
  • Hiding harmful files likea virus

  

9. Conclusion

 

            Steganography is a tool for concealing the very act of communication. It ensures Authentication Validation which verifies originator identification It is possible to hide Copyright Information such as ID of author and date of creation. In combination with cryptography, it provides a very secure mode of communication.

 

 

References

 

 

 

http://www.petitcolas.net/fabien/steganography/history.html

http://www.aljan.com.au/~wchan/stego.htm

http://www.wikipedia.com

Ioannis Pitas, Nikos Nikolaidis, “Copyright Protection of Images using    

Robust

Digital Signatures”, in IEEE International Conference on Acoustics,  

Speech and

Signal Processing (ICASSP-96), vol. 4, pp. 2168-2171, May 1996

David Kahn, “The History of Steganography”, in Proceedings of the First International Workshop, Cambridge, UK, May-June 1996, Springer.

Krenn, R., “Steganography and Steganalysis”

http://www.krenn.nl/univ/cry/steg/article.pdf

Moerland, T., “Steganography and Steganalysis”, Leiden Institute of Advanced Computing Science,

www.liacs.nl/home/ tmoerl/privtech.pdf

 

 


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