Steganography is defined as the art and science of hiding data behind some other data without the knowledge of the third party. It replaces bits of unused data into the usual file- graphics, sound, text, audio, video- with some other bits that have been obtained secretly or unauthorized manner.
Where as Cryptography is the science of writing in secret codes addresses all of the elements necessary for secure communication over an insecure channel, namely privacy, confidentiality, key exchange, authentication, and non-repudiation. But cryptography does not always provide safe communication.
The difference between steganography and cryptography is that in cryptography, one can tell that a message has been encrypted, but he cannot decode the message without knowing the proper key. In steganography, the message itself may not be difficult to decode, but most people would not detect the presence of the message. When combined, steganography and cryptography can provide two levels of security. Computer programs exist which encrypt a message using cryptography, and hide the encryption within an image using steganography.
Steganography has long been in use, even before the invention of the computer. For example, warring nations used invisible ink and microdots to communicate messages covertly. Computer technology has taken steganography to the next level. Nowadays, messages are typically hidden within digital images, video and audio.
Steganography has its place in security. It is not intended to replace cryptography but supplement it. Hiding a message with steganography methods reduces the chance of a message being detected.
Steganography Process
The information-hiding process in a steganographic system starts by identifying a cover medium’s redundant bits (those that can be modified without destroying that medium’s integrity).
The embedding process creates a stego medium by replacing these redundant bits with data from the hidden message. Three different aspects in information-hiding systems contend with each other: capacity, security, and robustness.
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 any damage
Payload - The information which is the be concealed.
Steganographic communication senders and receivers agree on a steganographic system and a shared secret key that determines how a message is encoded in the cover medium. To send a hidden message, for example, Mr.X creates a new image with a digital camera. Mr. X supplies the steganographic system with his shared secret and his message. The steganographic system uses the shared secret to determine how the hidden message should be encoded in the redundant bits.
The result is a stego image that Mr.X sends to Mr.Y. When Mr.Y receives the image, he uses the shared secret and the agreed on steganographic system to retrieve the hidden message.
Steganographic Methods
There are numerous methods used to hide information inside of Picture, Audio and Video files.
The two most common methods are:
· Least Significant Byte (LSB)
· Injection
Least Significant Byte (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, 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.
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. Nowadays, messages are typically hidden within digital images, video and audio.
· Steganography In Images
· Steganography In Audio
· Steganography In Video
· Steganography In Documents
Steganography In Images
When hiding information inside images the Least Significant Byte method is usually used. An image file is simply a file that shows different colors and intensities of light on different areas of an image.
The best type of image file to hide information inside of is a 24 Bit Bitmap image. When an image is of high quality and resolution it is a lot easier to hide and mask information inside of. It is important to remember that if you hide information inside of an image file and that file is converted to another image format, it is most likely the hidden information inside will be lost.
Steganography In Audio
Hiding information inside Audio files the technique usually used is low bit encoding which is similar to LSB that is used in Images. The problem with low bit encoding is that it is usually noticeable to the human ear.
Echo data hiding is yet another method of hiding information inside an audio file. By simply adding extra sound to an echo inside an audio file, information can be concealed.
Spread Spectrum is another method used to conceal information inside of an audio file. In this method adding random noises to the signal the information is conceal inside a carrier and spread across the frequency spectrum.
Steganography In Video
Discrete Cosine Transform method is used when hide information inside the video program.
DCT works by slightly changing the each of the images in the video, only so much though so it’s isn’t noticeable by the human eye. To be more precise about how DCT works, DCT alters values of certain parts of the images, it usually rounds them up.
Steganography In Documents
The use of Steganography in documents works by simply adding white space and tabs to the ends of the lines of a document.
This type of Steganography is extremely effective, because the use white space and tabs is not visible to the human eye at all. White space and tabs occur naturally in documents, so there isn’t really any possible way using this method of Steganography would cause someone to be suspicious.
Steganalysis: The Investigation of Hidden Information
The goal of steganography is to avoid drawing suspicion to the transmission of a hidden message. If suspicion is raised, then this goal is defeated.
The detection of steganographically encoded packages is called steganalysis.
The simplest method to detect modified files, however, is to compare them to the originals. To detect information being moved through the graphics on a website, for example, an analyst can maintain known-clean copies of these materials and compare them against the current contents of the site. The differences (assuming the carrier is the same) will compose the payload.
In general, using an extremely high compression rate makes steganography difficult, but not impossible; while compression errors provide a good place to hide data, high compression reduces the amount of data available to hide the payload in, raising the encoding density and facilitating easier detection.
Some of the techniques used in the manipulation of images are:
- Cropping
- Eliminating Image Portions
- Rotating Images
- Blurring
- Reducing Pixel Contrast
- Increasing Pixel Contrast
- Addition or Removal of Noise
- Addition of Bitwise Messages
Once detected, a Stego image hidden message can be modified. An automated tool used to detect the steganographed data in image is the Stegdetect. It is easy to detect various steganographics procedure to embed the secret data that is hidden within the images.
Misuse of Steganography-
Steganography is also used for sending malicious files such as Malware after hiding them inside the innocent documents such as images, pdf’ or word files.
When properly implemented, steganography can be difficult to detect, but not impossible. Steganography detection can be used to prevent communication of malicious data.
Steganography can make use of unlimited legal means to use any web site without attracting the attention of anybody, including the owners of the target web sites themselves, due to this it is sometime use for unsocial activities.
Related posts:
- Archive all your email messages
- How to Read Private Messages on Twitter
- Post and Receive Voice Messages in your Blog
- Secret Amazon Discount Finder Tool
- Post messages on twitter of more than 140 characters
|
|
Follow us on Twitter
Bookmark on del.icio.us
Become a Fan of Facebook
Add to Google Reader
Comments on this entry are closed.