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.
- 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
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,
Krenn, R., “Steganography and Steganalysis”
http://www.krenn.nl/univ/cry/steg/article.pdf
Moerland, T.,
“Steganography and Steganalysis”,
www.liacs.nl/home/ tmoerl/privtech.pdf
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