27-04-2011, 04:42 PM
Presented By:
Shishir Kumar Chanani
Vineet Vaibhav
Rahul Kumar Singh
[attachment=12962]
Steganography
The Art Of Hiding Information
What is steganography ?
Steganography is the practice of hiding private or sensitive information within something that appears to be nothing out of the usual
Steganography comes from the Greek words Steganós (Covered) and Graptos (Writing).
Steganographic Terms
Carrier File– A file which has hidden information inside of it.
Steganalysis – The process of detecting hidden information inside of a file.
Stego-Medium – The medium in which the information is hidden.
Redundant Bits – Pieces of information inside a file which can be overwritten or altered with out damaging the file.
We can define this simple formula:
Cover-medium + embedded-message = stego-message
Difference B/W cryptography & Steganography
Cryptography is secret writing. Anybody can see the message, but nobody else can read it. Usually, this is because its letters have been re-arranged, or replaced by different letters, according to some scheme that only the sender and receiver know.
Steganography is hidden writing. The message is there, but nobody notices it. However, once noticed, it can be read. A relatively modern example is the microdot, a page of text photographically reduced to the size of a full stop, and glued into an ordinary letter.
History of steganography
During World War 2 invisible ink was used to write information on pieces of paper.
In Ancient Greece they used to select messengers and shave their head, they would then write a message on their head.
Another method used in Greece was where someone would peel wax off a tablet that was covered in wax, write a message underneath the wax then re-apply the wax.
Basic Method Behind Steganography
How does it works
The two most common methods are LSB (Least Significant Byte) and Injection.
Substitution - Altering/Replacing The LSB : Least important areas of the file can be replaced with the information that is to be hidden, with out significantly altering the file or damaging it. This allows a person to hide information in the file and make sure that no human could detect the change in the file.
How does it works
Injection : Injection is quite a simple method which simply involves directly injecting the secret information into the carrier file. The main problem with this method is that it can significantly increase the size of the carrier file.
Types of steganography
Text Steganography : Since everyone can read, encoding text in neutral sentences is doubtfully effective. But taking the first letter of each word of the previous sentence, you will see that it is possible and not very difficult. Encoding secret messages in text can be a very challenging task. This is because text files have a very small amount of redundant data to replace with a secret message.
Types of steganography
Image Steganography :Coding secret messages in digital images is by far the most widely used of all methods in the digital world of today. This is because it can take advantage of the limited power of the human visual system (HVS)
Types of steganography
Audio Steganography :Because of the range of the human auditory system (HAS), data hiding in audio signals is especially challenging. The HAS perceives over a range of power greater than one billion to one and range of frequencies greater than one thousand to one. Also, the auditory system is very sensitive to additive random noise. Any disturbances in a sound file can be detected as low as one part in ten million (80dB below ambient level).
Image steganography
Large images are most desirable for steganography because they have the most space to hide data in.
In a computer, images are represented as arrays of values. These values represent the intensities of the three colors R(ed) G(reen) and B(lue), where a value for each of the three colors describes a pixel.
Image steganography
There are two common compression techniques used to shrink the file size of a bitmap.
GIF : The first is the GIF (Graphics Interchange Format) format, which will decrease the number of bits used to represent each pixel from 24 to 8. This is a lossless compression technique and the data hidden in the message can be recovered without a problem.
Image steganography
JPEG : The JPEG (Joint Photographic Experts Group) is a form of lossy compression. It does a very nice job of decreasing the file size of the image and retaining a great deal of its quality. The JPEG transformation takes eight pixel by eight pixel blocks and performs a 64 bit DCT (Discrete Cosine Transformation) does not compute to exact values. With continuing transforms, the precision of the calculation is decreased and the amount of error increases.
Image steganography
There are three main ways to conceal the secret message/image.
The first way is straight insertion where you just put the message into the cover image.
The next way requires some analysis to find the variations in color and it puts the message in those areas where it is less likely to be detected.
The last way is to randomly insert the message into the imageanography
LSB : Inserting an A into 3 pixels of a 24 bit image. Here is the original raster data:
The binary value of A is 10000011 and encoding A into the last bits of this 3 pixel sequence will change the above sequence to
Notice that only the underlined bits had to be changed in order to create the A.
Image steganography
Masking and Filtering :They hide info in a way simliar to watermarks on actual paper and are sometimes used as digital watermarks. Masking images entails changing the luminance of the masked area.
Contd…
Image steganography
Contd…
Image steganography
Changing the LSBs of the basic colours cannot be detected by a visual way, at least not on a computer screen. Changing, however, the last four bits of a colour byte could be detected visually. The reason for that is in the physiological characteristic of the human eyes
Contd…
Image steganography
Contd…
Image steganography
These are the steps followed in image hiding while transmission and de noising after receiving:
Get a cover image (publicly accessible material)
Take the information to be hidden (message or image)
Combine cover image with the information to be hidden(we follow LSB algorithm for this)
While transmission it will be corrupted by noise
Use any of the filtering methods, ex: wiener filtering for de noising in wavelet domain
Here filter is employed in order to remove the noise
During extraction a password check is provided
If password is matched then extraction of hidden information.
Contd…
Audio steganography
When hiding information inside Audio files the technique usually used is low bit encoding which is some what similar to LSB that is generally used in Images.
The problem with low bit encoding is that it is usually noticeable to the human ear, so it is a rather risky method for someone to use if they are trying to mask information inside of an audio file.
Audio steganography
Methods Of Hiding Information In Sound Track :
The carrier is a digitized audio information.
In case of digital sound CDs the sampling frequency standard is 44 kHz and the quantizing resolution is at least 12 bits.
That yields an amplitude scale of 4096 levels, in which changing the LSB means a 0.025 % relative modification which is essentially a distortion.
Such an extremely little distortion cannot be perceived by human ear.
In case of silent parts of a sound track it still may overheard.
Contd…
Audio Steganography
Methods Of Hiding Information In Sound Track :
Contd…
Both the hiding and the recovering technology is essentially the same as it was shown in case of covering pictures.
Naturally it needs computer and appropriate program.
Some commercial studio software are prepared in advance to insert e-watermarks.
Contd…
Text steganography
Text steganography
Contd…
Text steganography
Format-based methods used physical text formatting of text as a place in which to hide information. Generally, this method modifies existing text in order to hide the steganographic text.
Random and statistical generation is generating cover text according to the statistical properties . This method is based on character sequences and words sequences.
The final category is Linguistic method which is a scientific study of human nature here we generate the text according to the structure of language.
Contd…
Text steganography
Some ways to denote the letters of the carrier text to hide a secret message in it :
• Hardly visible dots below or above the selected letters or marking them by invisible ink. (Applied from ancient times)
• Hardly visible dislocation of the selected letters.
• Very little modification of the shapes of selected fonts
Contd…
Text steganography
Contd…
Text steganography
Methods to accomplish text based Steganography
Line-shift encoding
Word-shift encoding
Feature specific encoding
Contd…
Text steganography
Contd…
Detecting steganography
The art of detecting Steganography is referred to as Steganalysis.
There are many methods that can be used to detect Steganography such as:
Viewing the file and comparing it to another copy of the file found on the Internet (Picture File.): There are usually multiple copies of images on the Internet, so you may want to look for several of them and try and compare the suspect file to them.
Detecting steganography
Listening to the file : If you are trying to detect hidden information inside of a MP3 audio file you will need to find an audio file to compare it to that uses the same compression (MP3.) The same applies to finding hidden information inside Picture files.
Contd…
Uses of steganography
Steganography can be used anytime you want to hide data to prevent unauthorized persons from becoming aware of the existence of a message.
In the business world steganography can be used to hide a secret chemical formula or plans for a new invention.
Spies have used it since the time of the Greeks to pass messages undetected.
Conclusion
The meaning of Steganography is hiding information and the related technologies.
There is a principal difference between Steganography and Encryption, however they can meet at some points too.
They can be applied together, i.e. encrypted information can be hidden in addition.
Conclusion
To hide something a covering medium is always needed. (Picture, sound track, text or even the structure of a file system, etc.)
The technology of hiding should match the nature of the medium.
The covering medium must be redundant, otherwise the hidden information could be detected easily.
The hidden information should not be lost, if the carrying medium is edited, modified, formatted, re-sized, compressed or printed.
It’s an expectation as well, that the fact of hidden information should be impossible to detect by other then the addressee.
On the other hand security services should have methods to detect such information. At least its existence.
Shishir Kumar Chanani
Vineet Vaibhav
Rahul Kumar Singh
[attachment=12962]
Steganography
The Art Of Hiding Information
What is steganography ?
Steganography is the practice of hiding private or sensitive information within something that appears to be nothing out of the usual
Steganography comes from the Greek words Steganós (Covered) and Graptos (Writing).
Steganographic Terms
Carrier File– A file which has hidden information inside of it.
Steganalysis – The process of detecting hidden information inside of a file.
Stego-Medium – The medium in which the information is hidden.
Redundant Bits – Pieces of information inside a file which can be overwritten or altered with out damaging the file.
We can define this simple formula:
Cover-medium + embedded-message = stego-message
Difference B/W cryptography & Steganography
Cryptography is secret writing. Anybody can see the message, but nobody else can read it. Usually, this is because its letters have been re-arranged, or replaced by different letters, according to some scheme that only the sender and receiver know.
Steganography is hidden writing. The message is there, but nobody notices it. However, once noticed, it can be read. A relatively modern example is the microdot, a page of text photographically reduced to the size of a full stop, and glued into an ordinary letter.
History of steganography
During World War 2 invisible ink was used to write information on pieces of paper.
In Ancient Greece they used to select messengers and shave their head, they would then write a message on their head.
Another method used in Greece was where someone would peel wax off a tablet that was covered in wax, write a message underneath the wax then re-apply the wax.
Basic Method Behind Steganography
How does it works
The two most common methods are LSB (Least Significant Byte) and Injection.
Substitution - Altering/Replacing The LSB : Least important areas of the file can be replaced with the information that is to be hidden, with out significantly altering the file or damaging it. This allows a person to hide information in the file and make sure that no human could detect the change in the file.
How does it works
Injection : Injection is quite a simple method which simply involves directly injecting the secret information into the carrier file. The main problem with this method is that it can significantly increase the size of the carrier file.
Types of steganography
Text Steganography : Since everyone can read, encoding text in neutral sentences is doubtfully effective. But taking the first letter of each word of the previous sentence, you will see that it is possible and not very difficult. Encoding secret messages in text can be a very challenging task. This is because text files have a very small amount of redundant data to replace with a secret message.
Types of steganography
Image Steganography :Coding secret messages in digital images is by far the most widely used of all methods in the digital world of today. This is because it can take advantage of the limited power of the human visual system (HVS)
Types of steganography
Audio Steganography :Because of the range of the human auditory system (HAS), data hiding in audio signals is especially challenging. The HAS perceives over a range of power greater than one billion to one and range of frequencies greater than one thousand to one. Also, the auditory system is very sensitive to additive random noise. Any disturbances in a sound file can be detected as low as one part in ten million (80dB below ambient level).
Image steganography
Large images are most desirable for steganography because they have the most space to hide data in.
In a computer, images are represented as arrays of values. These values represent the intensities of the three colors R(ed) G(reen) and B(lue), where a value for each of the three colors describes a pixel.
Image steganography
There are two common compression techniques used to shrink the file size of a bitmap.
GIF : The first is the GIF (Graphics Interchange Format) format, which will decrease the number of bits used to represent each pixel from 24 to 8. This is a lossless compression technique and the data hidden in the message can be recovered without a problem.
Image steganography
JPEG : The JPEG (Joint Photographic Experts Group) is a form of lossy compression. It does a very nice job of decreasing the file size of the image and retaining a great deal of its quality. The JPEG transformation takes eight pixel by eight pixel blocks and performs a 64 bit DCT (Discrete Cosine Transformation) does not compute to exact values. With continuing transforms, the precision of the calculation is decreased and the amount of error increases.
Image steganography
There are three main ways to conceal the secret message/image.
The first way is straight insertion where you just put the message into the cover image.
The next way requires some analysis to find the variations in color and it puts the message in those areas where it is less likely to be detected.
The last way is to randomly insert the message into the imageanography
LSB : Inserting an A into 3 pixels of a 24 bit image. Here is the original raster data:
The binary value of A is 10000011 and encoding A into the last bits of this 3 pixel sequence will change the above sequence to
Notice that only the underlined bits had to be changed in order to create the A.
Image steganography
Masking and Filtering :They hide info in a way simliar to watermarks on actual paper and are sometimes used as digital watermarks. Masking images entails changing the luminance of the masked area.
Contd…
Image steganography
Contd…
Image steganography
Changing the LSBs of the basic colours cannot be detected by a visual way, at least not on a computer screen. Changing, however, the last four bits of a colour byte could be detected visually. The reason for that is in the physiological characteristic of the human eyes
Contd…
Image steganography
Contd…
Image steganography
These are the steps followed in image hiding while transmission and de noising after receiving:
Get a cover image (publicly accessible material)
Take the information to be hidden (message or image)
Combine cover image with the information to be hidden(we follow LSB algorithm for this)
While transmission it will be corrupted by noise
Use any of the filtering methods, ex: wiener filtering for de noising in wavelet domain
Here filter is employed in order to remove the noise
During extraction a password check is provided
If password is matched then extraction of hidden information.
Contd…
Audio steganography
When hiding information inside Audio files the technique usually used is low bit encoding which is some what similar to LSB that is generally used in Images.
The problem with low bit encoding is that it is usually noticeable to the human ear, so it is a rather risky method for someone to use if they are trying to mask information inside of an audio file.
Audio steganography
Methods Of Hiding Information In Sound Track :
The carrier is a digitized audio information.
In case of digital sound CDs the sampling frequency standard is 44 kHz and the quantizing resolution is at least 12 bits.
That yields an amplitude scale of 4096 levels, in which changing the LSB means a 0.025 % relative modification which is essentially a distortion.
Such an extremely little distortion cannot be perceived by human ear.
In case of silent parts of a sound track it still may overheard.
Contd…
Audio Steganography
Methods Of Hiding Information In Sound Track :
Contd…
Both the hiding and the recovering technology is essentially the same as it was shown in case of covering pictures.
Naturally it needs computer and appropriate program.
Some commercial studio software are prepared in advance to insert e-watermarks.
Contd…
Text steganography
Text steganography
Contd…
Text steganography
Format-based methods used physical text formatting of text as a place in which to hide information. Generally, this method modifies existing text in order to hide the steganographic text.
Random and statistical generation is generating cover text according to the statistical properties . This method is based on character sequences and words sequences.
The final category is Linguistic method which is a scientific study of human nature here we generate the text according to the structure of language.
Contd…
Text steganography
Some ways to denote the letters of the carrier text to hide a secret message in it :
• Hardly visible dots below or above the selected letters or marking them by invisible ink. (Applied from ancient times)
• Hardly visible dislocation of the selected letters.
• Very little modification of the shapes of selected fonts
Contd…
Text steganography
Contd…
Text steganography
Methods to accomplish text based Steganography
Line-shift encoding
Word-shift encoding
Feature specific encoding
Contd…
Text steganography
Contd…
Detecting steganography
The art of detecting Steganography is referred to as Steganalysis.
There are many methods that can be used to detect Steganography such as:
Viewing the file and comparing it to another copy of the file found on the Internet (Picture File.): There are usually multiple copies of images on the Internet, so you may want to look for several of them and try and compare the suspect file to them.
Detecting steganography
Listening to the file : If you are trying to detect hidden information inside of a MP3 audio file you will need to find an audio file to compare it to that uses the same compression (MP3.) The same applies to finding hidden information inside Picture files.
Contd…
Uses of steganography
Steganography can be used anytime you want to hide data to prevent unauthorized persons from becoming aware of the existence of a message.
In the business world steganography can be used to hide a secret chemical formula or plans for a new invention.
Spies have used it since the time of the Greeks to pass messages undetected.
Conclusion
The meaning of Steganography is hiding information and the related technologies.
There is a principal difference between Steganography and Encryption, however they can meet at some points too.
They can be applied together, i.e. encrypted information can be hidden in addition.
Conclusion
To hide something a covering medium is always needed. (Picture, sound track, text or even the structure of a file system, etc.)
The technology of hiding should match the nature of the medium.
The covering medium must be redundant, otherwise the hidden information could be detected easily.
The hidden information should not be lost, if the carrying medium is edited, modified, formatted, re-sized, compressed or printed.
It’s an expectation as well, that the fact of hidden information should be impossible to detect by other then the addressee.
On the other hand security services should have methods to detect such information. At least its existence.
