Project report on analysis of various spatial domain Steganography Algorithms.

1. Image Steganography

2. Steganography
Steganos
(Covered)
Graphein
(writing)

3. Steganography vs Cryptography
• Cryptography is the science of encrypting data in such a way that one
cannot understand the encrypted message, whereas in steganography the
mere existence of data is concealed, such that even its presence cannot be
noticed

4. COVER
Message
Embedding
Process
Stego-Object
Message
Communication
System

5. Input data used
• Cover of grayscale type (1000X674)
• Message of grayscale type (256x256)
• Why grayscale?

6. Cover Image
Message Image
Stego-Image

7. Embedding Algorithms

8. Least Significant Bit Substitution
Cover Image Message
Image
Calculate size of message (rows
,columns)
Convert each pixel value into
binary
Reserve first 20 pixels for hiding message
size information
Convert each pixel into
binary
Sequentially Replace LSB’s of cover
image pixels with message bit

9. Cover Image
Message Image
Stego-Image

10. Histogram of Cover Image Histogram of Stego Image

11. Difference between Histograms of Cover and
Stego Image

12. Size of Image Mean Square Error Peak Signal to Noise
Ratio
100% 0.177 128.1002
75% 0.1188 132.1314
50% 0.0532 140.1627
25% 0.0123 154.8155

13. LSB with Randomization
 Instead to sequentially replacing the LSB’s of pixels of cover image with
message bits ,the replacement is done on the basis of stego-key.
 Stego-key is a stream of pseudo random numbers which lie between 0 and
size of cover image

14. COVER
Message
Embedding
Process
Stego-Object
Message
Stego-key
Stego-key

15. Histogram of Cover Image Histogram of Stego Image

16. Difference between Histograms of Cover and
Stego Image

17. Size of Message Mean Square
Error
PSNR
100% 0.1904 127.4116
75% 0.1114 132.7703
50% 0.0501 140.7565
25% 0.0124 154.7397

18. Extraction
• Input: stego-image, key
• Step1: Convert the secret message into bit stream (Length L)
• Step2: Generate L number of pseudo random number using seed key
• Step3: for i=1 to L { Get lsb of pixel denoted by ith pixel position Append this lsb
into secret bit stream }
• Step4: Convert secret bit stream into secret message
• End Output: secret message

19. History…
• Shaving the head
• Wood tablet covered with wax
• Microdots
• Invisible ink
• Vexierbild
• Acrostic
• Paper mask

21. • Book : Hypnerotomachia Poliphili
• “ Poliam Frater Franciscus Columna peramavit”

22. Wisdom from cryptography…
We assume the method used to encipher the data is
known to the opponent, so the security must lie in
the choice of the key

23. Example of public key steganography
• One way to build public key steganography system is the use of
public key cryptosystem.
• Both cryptographic algorithms and embedding functions
assumed to be publicly known.
• ‘ Natural randomness’ indistinguishable from ciphertext.

24. Attackers..
• Active attacker is not able to change the cover and its semantics
entirely, but only make minor changes so that the original and
modified cover-objects stay perceptually or semantically similar.
• Malicious attacker forges messages or starts steganography
protocols under the name of one communication partner.

25. Active attackers…
• Steganographic system is extremely sensitive to cover modification.
• A system is called robust if the embedded information cannot be
altered without making drastic changes to stego-object.
• Trade-off between security and robustness.
• Two approaches to make steganography robust:
i. Making embedding process robust
ii. Reverse the modifications that have been applied.

26. Active attackers…
• Robust algorithms have to place the information in perceptually most
significant parts of the signal, since information encoded in noise
component can be removed without great effort.
• It is known that embedding rules operating in some transform domain of
cover signal can be much more robust to modification than embedding
algorithms operating in time domain.
• Information is hidden in plain sight, so obviously, in fact, that it is impossible
to modify without gross modifications to the transmitted object.

27. LSB matching
• In LSB replacement , the cover pixels with even values either
remain unchanged or are increased by 1, while inverse is true for
odd-valued pixels.
• LSB replacement can be easily detected.
• In LSB matching, 1 is either randomly added to or subtracted
from cover pixel value. It is much harder to detect.

28. Mielikainen’s improved LSB matching
• Embedding is performed using a pair of pixels as a unit, where
the LSB of the first pixel carries one bit of information, and a
function of two pixel values carries another bit of information.
• The modified method allows hiding the same payload as LSB
matching but with fewer changes to the cover image.

29. Cover…

30. Message…

31. Cover histogram..

32. LSB replacement stego histogram..

33. LSB matching stego histogram..

34. Comparison
0.25
0.2
0.15
0.1
0.05
0
Mean Squared Error
Simple LSB LSB with Randomization LSB Matching
100% 75% 50% 25%
MSE
Size of message

35. Thankyou