What is Steganography?
Steganography is the practice of hiding private or sensitive information within something that appears to be nothing out to 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. The difference between two is that steganography involves hiding information so it appears that no information is hidden at all. If a person or persons view the object that the information is hidden inside of he or she will have no idea that there is any hidden information, therefore the person will not attempt to decrypt the information.
History of Steganography
Throughout history, Steganography has been used to secretly communicate information between people.
Some examples of the use of Steganography is past times are:
- 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 milk, vinegar, and fruit juices were used because when each one of these substances is heated they darken and become visible to the human eye.
- 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 messenger’s hair to see the secreted message.
- During the “Cold War” period, US and USSR wanted to hide their sensors in the enemy’s facilities. These devices had to send data to their nations, without being spotted.
- Detecting Stega3.In WWII, the French Resistance sent some messages written on the backs of couriers using invisible ink.
- Messages written in Morse code on knitting yarn and then knitted into a piece of clothing worn by a courier.
- During World War II, a spy for Japan in New York City, Velvalee Dickinson, sent information to accommodation addresses in neutral South America. She was a dealer in dolls, and her letters discussed how many of this or that doll to ship. The stegotext was the doll orders, while the concealed “plaintext” was itself encoded and gave information about ship movements, etc. Her case became somewhat famous and she became known as the Doll Woman.
The art of detecting Steganography is referred to as Steganalysis.
To put is simply Steganalysis involves detecting the use of Steganography inside of a file. Steganalysis does not deal with trying to decrypt the hidden information inside of a file, just discovering it.
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. For example, if you download a JPED and your suspect file is also a JPED and the two files look almost identical apart from the fact that one is larger than the other, it is most probable you suspect file has hidden information inside of it.
Possible uses of Steganography
- Used to combine explanatory information with an image (like doctor’s notes accompanying an X-ray) but could accidentally degrade or render an image misleading.
- Embedding corrective audio or image data in case corrosion occurs from a poor connection or transmission but could counteract and be counterproductive with the original image.
- Peer-to-peer private communications, but doesn’t hide the fact that an e-mail was sent, negating the purpose of secret communications.
- Posting secret communications on the Web to avoid transmission but, someone else with a steganography detection and cracking tool could expose the message.
- Copyright protection a form of this already exists called digital watermarking but requires a use of separate hardware tools because steganographic software can’t use separate hardware tools. The steganographic software also can’t protect the watermark.
- Maintaining anonymity but easier to open free Web-based e-mail or use cloaked e-mail
- Hiding data on the network in case of a breach but better to understand and effectively use standardized encryption
How it works
The “cover” is the medium which is used to hide the secret information. The information to be hidden can be a plain text message, a cipher text, another image, or anything that can be represented in binary.
Cover media can be a lot of things: text, images, audio and video. As images are the most commonly used medium, let’s look at that closer.
Images can be altered in the noisy areas with a lot of color variations so that the alterations are less obvious. The message can also be scattered randomly throughout the image.
Common methods of concealing data in digital images include:
- Least significant bit insertion: This is a very popular method because of its simplicity. In this method, the LSB of each byte in the image is used to store the secret data. The resulting changes are too small to be recognized by the human eye. The disadvantage of this technique is that since it uses each pixel in an image, a lossless compression format like bmp or gif has to be used for the image. If lossy compression is used, some of the hidden information might be lost.
- Masking and filtering: These methods hide information in a manner similar to paper watermarks. This can be done, for example, by modifying the luminance of parts of the image. It does change the visible properties of an image, but if done with care the distortion is barely discernable. This method is much more robust than LSB modification with respect to compression since the information is hidden in the visible parts of the image.
- Transformations: This is a more complex way of hiding information in an image. Various algorithms and transformations are applied on the image to make hide information in it. DCT (Direct cosine transformation) is one such method. DCT is used by the JPEG compression algorithm to transform successive 8 x 8 pixel blocks of the image, into 64 DCT coefficients each. Steganography tools can use the LSB of the quantized DCT coefficient can be used to hide information. In addition to DCT, images can be processed with fast Fourier transformation and wavelet transformation. Other image properties such as luminance can also be manipulated.
Types of Steganography
- Image Steganography -Digital images are the most widely used cover objects for steganography. Due to the availability of various file formats for various applications, the algorithm used for these formats differs accordingly.
An image is a collection of bytes (know as pixels for images) containing different light intensities in different areas of the image. When dealing with digital images for use with Steganography, 8-bit and 24-bit per pixel image files are typical. Both have advantages and disadvantages 8-bit images are a great format to use because of their relatively small size. The drawback is that only 256 possible colors can be used which can be a potential problem during encoding. Usually, a grayscale color palette is used when dealing with 8-bit images such as (.GIF) because its gradual change in color would be harder to detect after the image has been encoded with the secret message. 24-bit images offer much more flexibility when used for Steganography. The large numbers of colors (over 16 million) that can be used go well beyond the human visual system (HVS), which makes it very hard to detect once a secret message, has been encoded.
- Audio Steganography – Implanting secret message into an audio is the most challenging technique in Steganography. This is because the human auditory system (HAS) has such a vibrant range that it can listen over. To put this in perspective, the (HAS) recognize over a range of power greater than one million to one and a range of frequencies greater than one thousand to one making it extremely hard to add or remove data from the original data structure. The only weakness in the (HAS) comes at trying to differentiate sounds (loud sounds drown out quiet sounds) and this is what must be exploited to encode secret messages in audio without being detected.
- Video Steganography – In video steganography, a video file would be embedded with supplementary data to hide secret messages. In the process, an intermediate signal which is a function of hidden message data and data of content signal would be generated. Content data (video file) is then combined with this intermediate signal to result in encoding. The supplementary data can include copy control data which can be brained by consumer electronic device and used to disable copying.