2. OVERVIEW
• What is Steganography?
• Cryptography vs. Steganography vs.
Watermarking
• Examples in History
• Motivation
• Steganography – Types
• Steganalysis
• Application
• References
3. What is Steganography?What is Steganography?
Stegosaurus: a covered lizard
Greek Words:
STEGANOS – “Covered”
GRAPHIA – “Writing”
• 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 can be achieve by concealing the
existence of information within seemingly
harmless carriers or covers (text, image,
video, audio, etc.)
– not encryption
• original image/file is intact
– not fingerprinting
• fingerprinting leaves separate file
describing contents
4. Cryptography
cryptos
hidden
graphia
writing
A secret manner of writing, … Generally, the art of writing
or solving ciphers.
-Crptography
Here the meaning of the message is changed…………….
The art of secret (covered or hidden) writing
-Steganography
Steganography
steganos graphia
covered writing
Cryptography vs. Steganography
5. Watermarking vs.
Steganography
Goal of steganography
– Intruder cannot detect a message
– Primarily 1:1 communication
Goal of watermarking
– Intruder cannot remove or replace the
message
– Primarily 1:many communication
8. Classical techniques
• Invisible ink (1st century AD - WW II).
• Roman general who shaved a slaves head and tattooed
a message on it
• Ancient Chinese wrote messages on silk, which was
then crunched into a tiny ball and covered by wax that
the messenger swallowed
• Overwrite select characters in printed type in pencil.
• Microdots (WW II).
• Newspaper clippings, knitting instructions, XOXO
signatures, report cards, etc…
9. Motivation
• Steganography received little attention in computing
• Renewed interest because of industry desire to protect
copyrighted digital work
– audio
– images
– video
– Text
• Detect counterfeiter, unauthorized presentation,
embed key, embed author ID
• Steganography ≠ Copy protection
10. Basics of Modern SteganographySteganography
fE: steganographic function "embedding"
fE-1: steganographic function "extracting"
cover: cover data in which emb will be hidden
emb: message to be hidden
key: parameter of fE
stego: cover data with the hidden message
11. Types of Steganography
• Steganography In Text/Documents
• Steganography In Images
• Steganography In Audio
• Steganography In TCP/IP Packets
12. Text Steganography
• Here the cover media or the “carrier” is a
text document.
• It is of 3 types- Format based, Random &
Statistical Generation and Linguistic
Method.
• Here we deal with only Format based
method.
13. Format Based Methods
Line Shift Coding
o text lines are vertically shifted to encode the
document.
o the decoding can be accomplished without
need of the original image/document, since
the original is known to have uniform line
spacing between adjacent lines within a
paragraph.
14. Format Based Methods
Word Shift Coding
o codewords are coded into a
document by shifting the
horizontal locations of words
within text lines.
o the largest and smallest
spaces between words for
each text-line are found and
the largest spacing is
reduced by a certain amount,
and the smallest is extended
by the same amount.
o This maintains the line length,
and produces little visible
changes to the text.
Feature Coding
• certain text features are
altered, or not altered,
depending on the codeword.
• For example, encoding bits
into text by extending or
shortening the upward,
vertical end lines of letters
such as b, d, h, etc.
• character endline lengths
would be randomly
lengthened or shortened,
then altered again to encode
the specific data.
• To decode, one requires the
original image
15. Text Steganography
• Text lines shifted up/down (40 lines text
⇒ 240
codes)
• word space coding
• character encoding - minor changes to
shapes of characters
16. Text Steganography
• Text lines shifted up/down (40 lines text
⇒ 240
codes)
• word space coding
• character encoding - minor changes to
shapes of characters
17. IMAGE ATTRIBUTES
• Digital images are made up of pixels
• The arrangement of pixels make up the
image’s “raster data”
• 8-bit and 24-bit images are common
• The larger the image size, the more
information you can hide. However,
larger images may require compression
to avoid detection.
18. REASONS FOR USING DIGITAL IMAGES
• It is the most widely used medium being
used today
• Takes advantage of our limited visual
perception of colors
• This field is expected to continually grow
as computer graphics power also grows
• Many programs are available to apply
steganography
19. IMAGE COMPRESSION
• Used for large files.
• 2 types – lossy & lossless
• Both save storage space
• But have different effects on the original
data.
• Lossy – high compression rate but no
integrity of originals.
• Lossless – low compression rate but
integrity of original data. Hence typically
used for Steganography.
21. LSB INSERTION
• Replaces least significant bits with the
message to be encoded
• Most popular technique when dealing
with images
• Simple, but susceptible to lossy
compression and image manipulation
22. LSB - Example
A sample raster data for 3 pixels (9 bytes)
may be:
Inserting
the binary
value for
A
(10000001)
changes
4 bits
00100111 11101000 11001000
00100110 11001000 11101000
11001001 00100111 11101011
00100111 11101001 11001000
00100111 11001000 11101001
11001000 00100111 11101011
23. LSB Continued…
• 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
24. 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
25. Static Parsing
Steganography(SPS)
• The sender and the receiver agree on a
cover image.
• The protocol does not modify the cover
image.
• Rather determines the bits of the secret
message that match the ones in the cover
image and stores their different locations
(i.e. in the cover image) in a vector.
• Then it is sent to the recipient.
26. SPS Algorithm
• Let Image1 be the cover image and Secret1 be the
secret message.
• The algorithm tries to find a match of all the bits of
Secret1 in Image1.
• If this is the case, it stores the indexes of the start and
end bits of Secret1 that occur within Image1 in an
output file Output1
• If not, the algorithm recursively tries to find a match of
the first and second halves of Secret1 in Image1.
• This Output1 is sent to the recipient.
• The running time is obtained from the recurrence
relation T (n) = 2T (n = 2) + O(n).
27. MASKING & FILTERING
• Masks secret data over the original data
by changing the luminance of particular
areas
• During masking, it embed the message
within significant bits of the cover image
• Not susceptible to lossy techniques
because image manipulation does not
affect the secret message
28. MASKING & FILTERING - Uses
• Digital Watermarking – provides
identification pertaining to the owner; i.e.
license or copyright information
- Invisible vs Visible
• Fingerprinting – provides identification
of the user; used to identify and track
illegal use of content
35. AUDIO STEGANOGRAPHY
• Range of Human auditory system(HAS)
is 20Hz-20KHz (dynamic range).
• Because of the sensitivity of HAS, data
hiding in audio signals is challenging.
• HAS has a fairly small differential range.
• Also what is important is the audio
storage & the transmission medium of
audio signal
• These have to be considered while data
hiding is done upon audio signals.
36. AUDIO STEGANOGRAPHY
Digital representation of audio signals
Sample quantization method : It is the
most popular format. Uses 16 bit linear
quantization. Introduces some distortion.
Temporal sampling rate : Most widely
used one is 8KHz.
37. AUDIO STEGANOGRAPHY
Transmission medium
4 transmission environments(env.)
possible.
Digital end-end environment
Increased/decreased resampling env.
Analog transmission & resampling
‘Over the air’ env.
38. Audio Data Hiding techniques
• Here we discuss 4 audio steganographic
techniques :
1.Low-bit encoding
2.Phase coding
3.Spread Spectrum
4.Echo data hiding.
39. Low-bit encoding
• Data is being hidden in least significant
bit(s) of audio samples.
• The weightage of LSBs in comparison with
the combined weightage of whole sample is
very small.
• Using more LSBs per sample increases the
capacity and decreases the transparency.
• There is always a trade-of between both
these parameters.
41. Phase coding
• Human Auditory System (HAS) can’t
recognize the phase change in audio signal
as easy it can recognize noise in the signal.
• The phase coding method works by
substituting the phase of an initial audio
segment with a reference phase that
represents the data, achieving an inaudible
encoding in terms of signal-to- noise ratio.
42. Phase coding
• The original sound sequence is broken into
a series of N short segments.
• DFT is applied to each segment, to break
create a matrix of the phase and magnitude.
• The phase difference between each
adjacent segment is calculated.
• For segment S0, the first segment, an
artificial absolute phase P0 is created
• For all other segments, new phase frames
are created
43. Phase coding Continued…
• The new phase and original magnitude are
combined to get a new segment, SN
• Finally, the new segments are concatenated
to create the encoded output.
44. Phase coding Continued…
The synchronization of the sequence is
done before the decoding.
The length of the segment, the DFT
points, and the data interval must be
known at the receiver.
The value of the underlying phase of the
first segment is detected as 0 or 1,which
represents the coded binary string.
45. Spread spectrum
• The encoded data is spread across as much
of the frequency spectrum as possible.
• Direct Sequence Spread Spectrum (DSSS)
encoding, spreads the signal by multiplying
it by a certain maximal length pseudo
random sequence(PN)
• Its frequency is much higher than that of
the original signal, thereby spreading the
energy of the original signal into a much
wider band.
46. Spread spectrum Continued…
• The resulting signal resembles white noise.
• This noise-like signal can be used to exactly
reconstruct the original data at the
receiving end, by multiplying it by the same
pseudorandom sequence
47. Echo data hiding
• Echo data hiding embeds data into a host
signal by introducing an echo.
• The data are hidden by varying three
parameters of the echo: initial amplitude,
decay rate and offset, or delay.
• The detection of the embedded signal then
just involves the detection of spacing
between the echoes.
48. STEGANOGRAPHY IN TCP/IP
PACKETS
• Protocols in the OSI network model have
vulnerabilities that can be used to hide
information.
• The TCP packet header has six
unused(reserved) bits and the IP packet
header has two reserved bits.
• They provide an excellent covert
communication channel if unchecked.
49. STEGANALYSIS
• Whereas the goal of steganography is the
avoidance of suspicion of hidden messages
in other data, steganalysis aims to discover
and render useless such covert messages.
• The basic purpose of Steganalysis is as a
penetration tool to test the
efficiency(Robustness, Capacity &
Imperceptibility)of a particular
Steganographic method.
51. STEGANALYSIS
Here 2 methods of Steganalysis are looked
into :
detecting messages or their transmission
disabling embedded information
52. DETECTING HIDDEN
INFORMATION
• Appended spaces and "invisible" characters can be
easily revealed by opening the file with a common
word processor.
• Some images may become grossly degraded with
even small amounts of embedded noise which will
give way the existence of hidden information.
• Echoes and shadow signals reduce the chance of
audible noise, but they can be detected with little
processing
• Filters can also be applied to capture TCP/IP packets
that contain hidden or invalid information in the
packet headers.
53. DISABLING STEGANOGRAPHY
• The disabling or removal of hidden information in
images comes down to image processing techniques
• For LSB methods of inserting data, simply using a
lossy compression technique, such as JPEG, is
enough to render the embedded message useless.
• Filters can be used in an attempt to cancel out
echoes or subtle signals that in in fact the actual
message thereby destroying the 'intended' message
in case of audio
• Reserved bits can be overwritten and passed along
without impacting the routing of the packet – TCP/IP
54. APPLICATIONS OF
STEGANOGRAPHY
• Confidential communication and secret
data storing
• Protection of data alteration
• Access control system for digital content
distribution
• Media Database systems
• Usage In Modern Printers
55. REFERENCES
• J.Altaay,S.Sahib and Mazdak Zamani, "An Introduction to Image
Steganography Techniques", in International Conference on
Advanced Computer Science Applications and Technologies,
2012, pp.122-126.
• S.Bhattacharyya, I.Banerjee and G.Sanyal, "A Novel Approach of
Secure Text Based Steganography Model using Word Mapping
Method(WMM)",in International Journal of Computer and
Information Engineering, 2010, pp.96-103
• Weiqi Luo, Fangjun Huang and Jiwu Huang,“Edge Adaptive Image
Steganography Based on LSB Matching Revisited”, IEEE
TRANSACTIONS ON INFORMATION FORENSICS AND SECURITY,
VOL. 5, NO. 2, JUNE 2010.
• http://en.wikipedia.org/wiki/Steganography
Fingerprinting … just imprint of the fingers onto a media file …
Cryptography some more insight…Cryptography is the study of hiding information, while Steganography deals with composing hidden messages so that only the sender and the receiver know that the message even exists. In Steganography, only the sender and the receiver know the existence of the message, whereas in cryptography the existence of the encrypted message is visible to the world. Due to this, Steganography removes the unwanted attention coming to the hidden message. Cryptographic methods try to protect the content of a message, while Steganography uses methods that would hide both the message as well as the content. By combining Steganography and Cryptography one can achieve better securityRead more: http://www.differencebetween.com/difference-between-cryptography-and-vs-steganography/#ixzz2vUFYIxbf
Watermarking ?? How??
This needs to be done …
So Steganography as such is not a new concept. It has been in news right from antiquity wherever there was a need for hiding some information. With the proliferation of digital media, it only took a new distinct form as Digital Steganography. Microdots: A microdot is text or an image substantially reduced in size onto a small disc to prevent detection by unintended recipients. Microdots are normally circular around one milli-metre in diameter but can be made into different shapes and sizes and made from various materials such as polyester and also metal.
Steganography ≠ Copy protection
Random :In order to avoid comparison with a known plaintext, steganographers often resort to generating
their own cover texts [7]. One method is concealing information in random looking sequence of
characters. In another method, the statistical properties of word length and letter frequencies are
used in order to create words which will appear to have same statistical properties as actual
words in the given language [2, 3].
Linguistic Steganography:Linguistic steganography specifically considers the linguistic properties of generated and
modified text, and in many cases, uses linguistic structure as the space in which messages are
hidden [7]. CFG create tree structure which can be used for concealing the bits where left
branch represents ‘0’ and right branch corresponds to ‘1’. A grammar in GNF can also be used
where the first choice in a production represents bit 0 and the second choice represents bit 1.
This method has some drawbacks. First, a small grammar will lead to lot of text repetition.
Secondly, although the text is syntactically flawless, but there is a lack of semantic structure.
The result is a string of sentences which have no relation to one another [7].
Most color laser printers and color copiers are designed to print invisible tracking codes across every single printed page of their output. These codes reveal which machine produced a document and, in some cases, when the document was printed or copied.The tracking dots your printer produces can be seen with a blue light, with a microscope, or with a scanner.