27-04-2011, 03:57 PM
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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 is often confused with cryptology because the two are similar in the way that they both are used to protect important information. Steganography comes from the Greek words Steganós (Covered) and Graptos (Writing).
More precisely,
“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.''
Steganography includes a vast array of techniques for hiding messages in a variety of media. Among these methods are invisible inks, microdots, digital signatures, covert channels and spread-spectrum communications. Today, thanks to modern technology, steganography is used on text, images, sound, signals, and more.
The advantage of steganography is that it can be used to secretly transmit messages without the fact of the transmission being discovered. Often, using encryption might identify the sender or receiver as somebody with something to hide. For example, that picture of your cat could conceal the plans for your company's latest technical innovation.
However, steganography has a number of disadvantages as well. Unlike encryption, it generally requires a lot of overhead to hide a relatively few bits of information. However, there are ways around this. Also, once a steganographic system is discovered, it is rendered useless. This problem, too, can be overcome if the hidden data depends on some sort of key for its insertion and extraction.
In fact, it is common practice to encrypt the hidden message before placing it in the cover message. However, it should be noted that the hidden message does not need to be encrypted to qualify as steganography. The message itself can be in plain English and still be a hidden message. However, most steganographers like the extra layer of protection that encryption provides. If your hidden message is found, and then at least make it as protected as possible.
This seminar aims to outline a general introduction to steganography - what it is, and where it comes from. Methods for hiding data in three varied media (text, image, and audio) will be described, and some guidelines for users of steganography will be provided where necessary. In addition, we will take a brief look at steganalysis, the science of detecting steganography, and destroying it.
Steganographic Terms :
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 stego-medium
Stego-medium: This is the final piece of information that the casual observer can see.
We can define this simple formula:
Cover-medium + embedded-message = stego-message
Difference Between Steganography & 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.
In this way, we can say that steganography completes cryptography, and actually there are usually two ciphers to break when trying to extract the embedded message: one is the one with which the message was embedded, and the other is the one with which the message was enciphered
History of Steganography :
Throughout history Steganography has been used to secretly communicate information between people.
Some examples of use of Steganography in past times are:
1. During World War 2 invisible ink was used to write information on pieces of paper so that the paper appeared to the average person as just being blank pieces of paper. Liquids such as urine, milk, vinegar and fruit juices were used, because when each one of these substances are heated they darken and become visible to the human eye.
2. In Ancient Greece they used to select messengers and shave their head, they would then write a message on their head. Once the message had been written the hair was allowed to grow back. After the hair grew back the messenger was sent to deliver the message, the recipient would shave off the messengers hair to see the secret message.
3. 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. The recipient of the message would simply remove the wax from the tablet to view the message.
Basic Method Behind Steganography :
Steganography embeds a secret message in a cover message, this process is usually parameterized by a stego-key, and the detection or reading of an embedded information is possible only having this key.
How Does It Works :
There are numerous methods used to hide information inside of Picture, Audio and Video files.
The two most common methods are LSB (Least Significant Byte) and Injection.
I will discuss these two methods below.
Substitution - Altering/Replacing the LSB
When files are created there are usually some bytes in the file that aren't really needed, or at least aren't that important. These areas of the file can be replaced with the information that is to be hidden, without 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. The LSB method works best in Picture files that have a high resolution and use many different colors, and with Audio files that have many different sounds and that are of a high bit rate. The LSB method usually does not increase the file size, but depending on the size of the information that is to be hidden inside the file, the file can become noticeably distorted.
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.
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)
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).
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 is often confused with cryptology because the two are similar in the way that they both are used to protect important information. Steganography comes from the Greek words Steganós (Covered) and Graptos (Writing).
More precisely,
“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.''
Steganography includes a vast array of techniques for hiding messages in a variety of media. Among these methods are invisible inks, microdots, digital signatures, covert channels and spread-spectrum communications. Today, thanks to modern technology, steganography is used on text, images, sound, signals, and more.
The advantage of steganography is that it can be used to secretly transmit messages without the fact of the transmission being discovered. Often, using encryption might identify the sender or receiver as somebody with something to hide. For example, that picture of your cat could conceal the plans for your company's latest technical innovation.
However, steganography has a number of disadvantages as well. Unlike encryption, it generally requires a lot of overhead to hide a relatively few bits of information. However, there are ways around this. Also, once a steganographic system is discovered, it is rendered useless. This problem, too, can be overcome if the hidden data depends on some sort of key for its insertion and extraction.
In fact, it is common practice to encrypt the hidden message before placing it in the cover message. However, it should be noted that the hidden message does not need to be encrypted to qualify as steganography. The message itself can be in plain English and still be a hidden message. However, most steganographers like the extra layer of protection that encryption provides. If your hidden message is found, and then at least make it as protected as possible.
This seminar aims to outline a general introduction to steganography - what it is, and where it comes from. Methods for hiding data in three varied media (text, image, and audio) will be described, and some guidelines for users of steganography will be provided where necessary. In addition, we will take a brief look at steganalysis, the science of detecting steganography, and destroying it.
Steganographic Terms :
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 stego-medium
Stego-medium: This is the final piece of information that the casual observer can see.
We can define this simple formula:
Cover-medium + embedded-message = stego-message
Difference Between Steganography & 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.
In this way, we can say that steganography completes cryptography, and actually there are usually two ciphers to break when trying to extract the embedded message: one is the one with which the message was embedded, and the other is the one with which the message was enciphered
History of Steganography :
Throughout history Steganography has been used to secretly communicate information between people.
Some examples of use of Steganography in past times are:
1. During World War 2 invisible ink was used to write information on pieces of paper so that the paper appeared to the average person as just being blank pieces of paper. Liquids such as urine, milk, vinegar and fruit juices were used, because when each one of these substances are heated they darken and become visible to the human eye.
2. In Ancient Greece they used to select messengers and shave their head, they would then write a message on their head. Once the message had been written the hair was allowed to grow back. After the hair grew back the messenger was sent to deliver the message, the recipient would shave off the messengers hair to see the secret message.
3. 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. The recipient of the message would simply remove the wax from the tablet to view the message.
Basic Method Behind Steganography :
Steganography embeds a secret message in a cover message, this process is usually parameterized by a stego-key, and the detection or reading of an embedded information is possible only having this key.
How Does It Works :
There are numerous methods used to hide information inside of Picture, Audio and Video files.
The two most common methods are LSB (Least Significant Byte) and Injection.
I will discuss these two methods below.
Substitution - Altering/Replacing the LSB
When files are created there are usually some bytes in the file that aren't really needed, or at least aren't that important. These areas of the file can be replaced with the information that is to be hidden, without 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. The LSB method works best in Picture files that have a high resolution and use many different colors, and with Audio files that have many different sounds and that are of a high bit rate. The LSB method usually does not increase the file size, but depending on the size of the information that is to be hidden inside the file, the file can become noticeably distorted.
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.
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)
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).