1. Steganography The Art of Hiding Messages

2. introduction Word steganography comes from the Greek
means covered or secret writing.
word steganos = “covered”
word graphie = “writing”

3. History
Head of messenger.
Invisible ink
Chemical substances
More …

4. introduction steganography = stego
mentioned during the investigation of the September 11 attacks
terrorists used it to hide their attack plans, maps, and activities in chat rooms, bulletin boards, and Web sites.
widely used
long before these attacks
with many other technologies
its use has increased due to the popularity of the Internet.

5. introduction Definition
it is the technique of embedding (or substitution) information into something else for the sole purpose of hiding that information from the casual observer.

6. Technical Steganography
Information hiding
Covert channels
Technical Steganography
Steganography
Linguistic Steganography
Watermarking
Anonymity
Robust Copyright marking
Fingerprinting
Copyright
marking
Imperceptible
watermarking
Fragile Watermarking
Visible
watermarking

7. introduction steganography Vs watermarking
method of hiding trademark information in
images, music, and software.
not considered a true form of steganography.
Types
Invisible
Invisible intended to be imperceptible to the human eye or inaudible. the watermark can only be determined through watermark extraction or detection by computers.
Visible
Visible such as a company logo stamped on an image or Video.

8. introduction In stego The main goal: is in one-to-one communications
to hide a message m
in (cover) data c
to obtain new data c'
practically indistinguishable from c (by people)
in such a way that an eavesdropper cannot detect the presence of m in c'.
in one-to-one communications
the information is hidden in the image, audio or video

9. introduction watermarking The main goal: is to hide a message m
in (cover) data c,
to obtain new data c',
practically indistinguishable from c (by people)
in such a way that an eavesdropper cannot remove or replace m in c'.
in one-to-many communications
adds something to the image, it becomes part of the image, audio or video.

10. introduction ??? related but !encryption Cryptography
hides the contents of the message from an attacker, but not the existence of the message.
drawbacks of using encryption
recognized as an encrypted message.(raise suspicion).
provides confidentiality but not secrecy.
???
@2*$#d(*%7*

11. introduction Steganography
hide the very existence of the message in the communicating data.
Good of using steganography
the information is hidden (text, images, and sound files.)
looking at a HOST file would not be able to determine if there was any information within it.

12. introduction advantageous to use encryption and stego by
first encrypting the data
then using steganography to hide it.
not be able to read the data it extracted because it is encrypted.

13. steganographic systems

14. Hiding the Data
data injection
Substitution

15. Payload (secret message)
Hiding the Data
data injection
the secret message is directly embedded in the host medium.
Problem:
makes the host file larger
easier to detect.
Keep a secret
Cover object
Payload (secret message)
Stego-object
New size

16. Substitution Hiding the Data results quality of the original host file
the normal data is replaced or substituted with the secret data.
results
very little size change for the host file.
quality of the original host file
depending on the type of
host file
amount of hidden data

17.
cover
Secret data
Extracting
Embedding
LSB Steganography
Replacing least-significant-bits (LSBs) of digital data with message bits.

18. Secret Message inserted Cover Image Stego-Image 1 102 103 104 105 106
102
103
104
105
106
108
109
201
202
203
204
205
206
207
185
187
188
189
191
192
194
195
197
198
199 51 56 61 66 71 76 81 86 90 95
100
110
115
120
135
161
163
164
168
171
173
174
176
179
181
183
186
190
Secret
Message
inserted
103
102
105
106
108
109
200
201
202
203
204
205
206
207
185
187
188
189
191
192
194
195
197
198
199 51 56 61 66 71 76 81 86 90 95
100
110
115
120
135
161
163
164
168
171
173
174
176
179
181
183
186
190
Cover Image
Stego-Image

19. restrictions to using stego:
Hiding the Data
restrictions to using stego:
MSG(bytes) <= HOST(room)
The data that is hidden in the file should
not significantly degrade the host file. The hidden data should be as imperceptible as possible.
be encoded directly into the media and not placed only in the header or in some form of file wrapper. The data should remain consistent across file formats.
be immune to modifications from data manipulations such as filtering or resampling.
still be recoverable even if only portions of the host image are available.
Because the hidden data can degrade or distort the host file, error-correction techniques should be used to minimize this condition.

20. Steganography in Image Files
A computer image is
an array of pixels
pixels
represented as light intensity.
stored in either
24 -bit pixel files
8-bit pixel files

21. Steganography in Image Files
In a 24-bit image
there is more room to hide information
Very large in size
not the ideal choice
for posting them on Web sites or transmitting over the Internet.
For example
a 24-bit image 1024X768  size about 2 MB.
Solution : compression.
lossy
lossless compression.

22. Steganography in Image Files
Effect of
Lossy compression on the hidden information
provides high compression rates, but at the expense of data image integrity loss.
lose some of the image quality.
An example of a lossy compression format is JPEG (Joint Photographic Experts Group).
Lossless compression on the hidden information
does not lose image integrity
the favored compression used for steganography.
GIF and BMP files are examples of lossless compression formats.

23. Steganography in Image Files
In an 8-bit image
each pixel is represented by eight bits
The four bits to the
left are the most-significant bits (MSB)
right are the least-significant bits (LSB).
Changes to the
MSB : will result in a drastic change in the color and the image quality
LSB : will have minimal impact.

24. Steganography in Image Files
The human eye cannot usually detect changes to only one or two bits of the LSB.
if we hide data in any two bits in the LSB, the human eye will not detect it.
Example:
bit pattern =
New pattern =
This is why the art of steganography uses these LSBs to store the hidden data.

25. Ideas Image segmentation ME steganography – Maximum Error Image Mosaic
The algorithm divides a binary image into noise like region and signal region.
If a region is too simple to hide information, a conjugate operation is introduce, which can convert a simple pattern into a complex pattern without lose any shape information.
ME steganography – Maximum Error
The algorithm takes advantage of local characteristics of a cover-image to embed maximal amount of message in the cover and maintain the imperceptible alteration.
Image Mosaic
The sender and the receiver share the same image database.
Each tile image corresponds to an integer.
Embedding algorithm chose different tile image according to secret message.
The Receiver extract message from tile images.

26. Ideas Weighted matrix Histogram preserve
Embed r bits of data into image block by changing at most X bits.
This algorithm can hide as many as bits of data in the image by changing at most X bits in the image block.
This scheme can provide higher security, embed more data, and maintain higher quality of the host image.
Histogram preserve
This algorithm based on histogram preserving data mappings (HPDM).
Cachin defined a system is perfectly secure when the statistics of the stego-image and the cover image are identical, i.e., the relative entropy between the cover and stego is zero.
Based on this definition, Eggers proposed his algorithm that preserves the histogram of the cover image.

27. A Practical Example
the host file before a hidden file has been introduced.

28. A Practical Example
the image file we wish to hide

29. A Practical Example Using a program called Invisible Secrets
1st is inserted into 2nd .
The resulting image file is 

30. M C K F D C’
F: M*CC`
D:C`M

31. MSG(bytes) <= HOST(room)  M(bytes) <= C(room)
M: secret message.
C: cover message.
F: embedding function.
function must have inverse at the domain.
D: extracting function. D(F(C,M))M
MSG(bytes) <= HOST(room)  M(bytes) <= C(room)

32. Types
1. Public key steganography Public key Private key

33. Types 2. Pure steganography: F: M*CC` D:C`M C cover
C cover
M Secret data
Perform the F: M*CC`

34. C cover Perform the D:C`M 11011101 00101100 00011101 00001100
C cover
M Secret data
F Embedding
Perform the D:C`M

35.
C` Stego-Object
D Extracting

36.
C cover
M Secret data
D Extracting
F Embedding

37. Steps to secure and invisible Data Hiding in 2-color Images
Types
3. Secret key steganography
F: K*M*CC`
D:K*C`M
Steps to secure and invisible Data Hiding in 2-color Images

38. Basics - Weighted matrix
Hiding
apiece of critical information
in binary image.
In each M x N image block of a host image
log2(mn+1) bits can be hidden in the block
by changing at most 3 bits in the block.
We are given a host binary image F.
F will be partitioned into blocks of fixed size M*N  F1, F2, …Fi
can hid r= log2(mn+1) bits in each block.
secret key
K: a randomly selected binary matrix of size m x n.
W: a weight matrix which is an integer matrix of size m x n, where Wi,j ={1,2,….2r-1}

39. STEPS 1- compute FiΦK 2 - compute SUM((Fi ΦK)ΘW)
where Φ  XOR of two equal size binary matrices.
2 - compute SUM((Fi ΦK)ΘW)
where
Θ  bitwise multiplication of two equal-size matrices
SUM  the sum of all elements in a matrix.

40. STEPS 3- Compute d as follow 4- the receiver compute
IF the secret message is (b1,b2…br(
d= (b1,b2…br( - SUM((Fi ΦK)ΘW) mod 2r
If d=0
no need to change Fi to Fi`
otherwise, we will change Fi to Fi`
to make d=0.
4- the receiver compute
SUM((Fi ΦK)ΘW) mod 2r
to find the hidden message

41. Example Let a host image F, and secret key K, w 1 4 3 2 1 7 6 5 1 1 F=1 4 3 2 1 7 6 5 1 1 F= K= W=

42. Example F is partitioned into two 4*4 blocks(F1,F2), in binary image.
In each M x N image block of a host image
log2(mn+1) bits can be hidden in the block
F is partitioned into two 4*4 blocks(F1,F2), 1 F1 F2

43. Example We can hide r< log2(4*4+1) bits in each block.
Let r=3, be the secret data to be hidden.
r1=001 =1, r2=001 =1

44. compute Fi ΦK 1 1 F= K= 1
F1 ΦK
F2 ΦK

45. compute ((Fi ΦK)ΘW) SUM((F1 ΦK)ΘW) =24 SUM((F2 ΦK)ΘW) =36 1 4 3 2 1 71 4 3 2 1 7 6 5 W=
(F1 ΦK)
(F2 ΦK) 2 4 1 7 6 5 3
((F1 ΦK)ΘW)
((F2 ΦK)ΘW)
SUM((F1 ΦK)ΘW) =24
SUM((F2 ΦK)ΘW) =36

46. so we must increase the sum by 1 to make d =0 by swapping[F1]2,4
d= (b1,b2…br(- SUM((Fi ΦK)ΘW) mod 2r
If d=0, there is no need to change Fi to Fi`, otherwise, we will change Fi to Fi`, to make d=0
24 mod 23= 0, d=1-0=1
so we must increase the sum by 1 to make d =0 by swapping[F1]2,4 1

47. 36 mod 23 =4, d=1-4=-3.
So we must decrees the sum by 3 to make d= 0 by swapping [F2]2,2 and [F2]3,2 will increase the sum by -6, and 3. 1

48. image F will be 1 1

49. receiver
compute SUM((Fi ΦK)ΘW) mod 2r to find the hidden message.

50. Practical & illegal Uses
practical uses
store password information on an image file on a hard drive or Web page.
In applications where encryption is not appropriate (or legal), stego can be used for covert data transmissions.
has been used mainly for military operations, it is now gaining popularity in the commercial marketplace.
illegal uses
it was reported that terrorists use this technology to hide their attacks plans.
Child pornographers have also been known to use stego to illegally hide pictures inside other images.

51. Defeating Steganography
Steganalysis
is the technique of
discovering and
recovering the hidden message.
a steganalyst (detect) < > a cryptanalyst (decode)
attempt to
detect the existence of hidden information in messages.

52. Defeating Steganography
the main goal
is to determine
if the image has a hidden message and
the specific steganography algorithm used to hide the information.
Attacks
stego-only, known cover, known message, chosen stego, and chosen message.
In a stego-only attack
the stego host file is analyzed.

53. Defeating Steganography
A known cover attack
is used if both the original (unaltered) media and the stego-infected file are available. A known message attack is used when the hidden message is revealed.
A chosen stego attack
is performed when the algorithm used is known and the stego host is available.
A chosen message attack
is performed when a stego-media is generated using a predefined algorithm. The resulting media is then analyzed to determine the patterns generated, and this information is used to compare it to the patterns used in other files. This technique will not extract the hidden message, but it will alert the steganalyst that the image in question does have embedded (and hidden) information.

54. Defeating Steganography
dictionary attacks
Another attack method is using against steganographic systems.
This will test to determine if there is a hidden image in the file.
All of the stenographic systems used to create stego images use some form of password validation. An attack could be perpetrated on this file to try to guess the password and determine what information had been hidden. Much like cryptographic dictionary attacks, stego dictionary attacks can be performed as well. In most steganographic systems, information is embedded in the header of the image file that contains, among other things, the length of the hidden message. If the size of the image header embedded by the various stego tools is known, this information could be used to verify the correctness of the guessed password.

55. Defeating Steganography
Protecting yourself against steganography is not easy. If the hidden text is embedded in an image, and you have the original (unaltered) image, a file comparison could be made to see if they are different. This comparison would not be to determine if the size of the image has changed—remember, in many cases the image size does not change. However, the data (and the pixel level) does change. The human eye usually cannot easily detect subtle changes—detection beyond visual observation requires extensive analysis. Several techniques are used to do this. One is the use of stego signatures. This method involves analysis of many different types of untouched images, which are then compared to the stego images. Much like the analysis of viruses using signatures, comparing the stego-free images to the stego-images may make it possible to determine a pattern (signature) of a particular tool used in the creation of the stego-image.

56. Steganography Tools Steganos S-Tools (GIF, JPEG) StegHide (WAV, BMP)
Invisible Secrets (JPEG)
JPHide
Camouflage
Hiderman
Many others…

57. ASS Discussion Report Steganography Applications
Chose two of the following attacks to be described and its defense: stego-only, known cover, known message, chosen stego, and chosen message.

58. LAB chose one tool to write a report showing its usage.
Develop an application for the presented Weighted Matrix secret key Steganography