25-04-2012, 12:22 PM
steganography
STEGNOGRAPHY.pdf (Size: 82.39 KB / Downloads: 56)
INTRODUCTION
Steganography comes from the Greek and literally means,
"Covered writing". It is one of various data hiding techniques, which
aims at transmitting a message on a channel where some other kind of
information is already being transmitted. This distinguishes
steganography from covert channel techniques, which instead of trying
to transmit data between two entities that were unconnected before.
The goal of steganography is to hide messages inside other
“harmless” messages in a way that does not allow any “enemy” to
even detect that there is a second secret message present. The only
missing information for the “enemy” is the short easily exchangeable
random number sequence, the secret key, without the secret key, the
“enemy” should not have the slightest chance of even becoming
suspicious that on an observed communication channel, hidden
communication might take place.
STEGANOGRAPHY AND CRYPTOGRAPHY
Steganography and cryptography are cousins in spy-craft
family. Cryptography scrambles a message so it cannot be understood.
Steganography hides the message so it cannot be seen. 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.
Some history
The first description of the use of steganography dates back
to the Greeks. Herodotus tells how a message was passed to the
Greeks about Xerses’ hostile intentions underneath the wax of a
writing tablet, and describes a technique of dotting successive letters
in a cover text with a secret ink, due to Aeneas the Tactician.
SOME DEFINITIONS
We give some definitions common to the steganography field:
Cover medium: This is the medium in which we want to hide data, it
can be an innocent looking piece of information for steganography, or
some important medium that must be protected for copyright or
integrity reasons.
Embedded message: This is the hidden message we want to put in the
cover. It can be some data for steganography and some copyright
informations or added content for digital watermarking.
Stegokey: This is represented by some secret information, which is
needed in order to extract the embedded message from the stegomedium
File compression
There are two types of file compression methods- lossless
and lossy. Both methods save storage space but have different results,
interfer9ing with the hidden information, when information is
uncompressed. Lossless compression lets us reconstruct the original
message exactly; therefore it is preferred when the original
information must remain intact (as with steganographic images).
Lossless compression us typical of mages saved as GIF and 8-bit
BMP.
Robustness
Spread spectrum techniques are usually quite robust. Every
transformation that adds noise to the image isn’t able to destroy the
message. Anyway, a determined attacker can quite easily compromise
the embedded data using some digital processing, like for example
Steganography - Seeing the Unseen
noise reduction filters, the same that are used in decoding to estimate
the original cover.
CONCLUSION
In this paper we tried to give an all-round view of
steganography, both used to exchange messages and watermarking.
First we gave an outline of the problem, telling also some of the
history of this quickly developing field.
STEGNOGRAPHY.pdf (Size: 82.39 KB / Downloads: 56)
INTRODUCTION
Steganography comes from the Greek and literally means,
"Covered writing". It is one of various data hiding techniques, which
aims at transmitting a message on a channel where some other kind of
information is already being transmitted. This distinguishes
steganography from covert channel techniques, which instead of trying
to transmit data between two entities that were unconnected before.
The goal of steganography is to hide messages inside other
“harmless” messages in a way that does not allow any “enemy” to
even detect that there is a second secret message present. The only
missing information for the “enemy” is the short easily exchangeable
random number sequence, the secret key, without the secret key, the
“enemy” should not have the slightest chance of even becoming
suspicious that on an observed communication channel, hidden
communication might take place.
STEGANOGRAPHY AND CRYPTOGRAPHY
Steganography and cryptography are cousins in spy-craft
family. Cryptography scrambles a message so it cannot be understood.
Steganography hides the message so it cannot be seen. 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.
Some history
The first description of the use of steganography dates back
to the Greeks. Herodotus tells how a message was passed to the
Greeks about Xerses’ hostile intentions underneath the wax of a
writing tablet, and describes a technique of dotting successive letters
in a cover text with a secret ink, due to Aeneas the Tactician.
SOME DEFINITIONS
We give some definitions common to the steganography field:
Cover medium: This is the medium in which we want to hide data, it
can be an innocent looking piece of information for steganography, or
some important medium that must be protected for copyright or
integrity reasons.
Embedded message: This is the hidden message we want to put in the
cover. It can be some data for steganography and some copyright
informations or added content for digital watermarking.
Stegokey: This is represented by some secret information, which is
needed in order to extract the embedded message from the stegomedium
File compression
There are two types of file compression methods- lossless
and lossy. Both methods save storage space but have different results,
interfer9ing with the hidden information, when information is
uncompressed. Lossless compression lets us reconstruct the original
message exactly; therefore it is preferred when the original
information must remain intact (as with steganographic images).
Lossless compression us typical of mages saved as GIF and 8-bit
BMP.
Robustness
Spread spectrum techniques are usually quite robust. Every
transformation that adds noise to the image isn’t able to destroy the
message. Anyway, a determined attacker can quite easily compromise
the embedded data using some digital processing, like for example
Steganography - Seeing the Unseen
noise reduction filters, the same that are used in decoding to estimate
the original cover.
CONCLUSION
In this paper we tried to give an all-round view of
steganography, both used to exchange messages and watermarking.
First we gave an outline of the problem, telling also some of the
history of this quickly developing field.