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Hide and seek
Steganography — the practice of hiding information is perhaps as old as the art of communication itself. Steganography aims not only at disguising the message (as in encryption) but to hide the very existence of the disguised message.
Literally, the word “steganogra- phy” comes from the Greek word “steganos”, which means secret, and “graphy”, which means writing. The field has matured is now an established area of research in the field of computing.
Free steganography tools not only provide data protection but are also being used to produce digital watermarking and hidden copyright messages in images and other multimedia files.
Digital data often contain ‘spaces’ which can be altered without any apparent changes in their rendered form. Let us take an example of a sound file. For computers, it is a sequence of bytes if seen at lower level (that is, how a file is composed).
Let us suppose that the file sequence is “120 140 160… .” In byte (having 8 bits) representation, decimal 120 would be 1111000. Here, we want to hide the number decimal 2, that is, binary 10. From the 8-bits of decimal 120, replacing the trailing 0 with 1, and then replacing the right-most bit of binary 140 with 0, we can successfully hide binary 10 by placing them at the least significant positions of 120 and 140 respectively.
This gives a new byte sequence, 121 141 160 and so on. Fortunately, even though the first two bytes have changed as well, the file sound will remain the same.
Unlike some other file formats, sound and pictures files are “read” rather normally by applications even if there is a slight alteration in them. Also, there is human limitation of detecting very small changes when it comes to audio and graphics comprehension.
Image information can be similarly altered, and the best part is that since we are making use of existing bit patterns, the file size does not increase substantially.
Some steganography tools employ compression as well. Here, in order to avoid detection of hidden text, data are often spread out randomly or in a seemingly random fashion, which is recreated using user-provided seed.
There is always a risk that, though distributed, the data are still in plain format and can be detected. This is a probable scenario and to counter this, the data to be hidden are first encrypted using a password, which is essential at the time of revealing the covert information.
Use of industry standard encryption algorithms like triple DES, AES, Blow Fish, and IDEA make steganography a very potent mechanism of keeping data out of prying eyes and transfer it without arousing suspicion.
Free tools
S-Tools 4 is one of the most popular freely available steganogr- aphy tools. It can hide data in BMP, GIF or WAV files. The usage is fairly simple. The application provides an action window in which the carrier file (file in which another file is to be hidden) can be dragged and dropped.
The next step is to drag the file to be hidden over the carrier. This results in a password prompt and algorithm selection box. As a general rule, avoid DES since it is one of the less secure algorithms.
The program then asks if the image is to be converted to 24-bits or whether it should attempt colour reduction. In the former case, note that transferring large images can be a telltale sign of steganography. So go for the second option.
One handy option of S-Tools is the calculation of the size of data that a carrier can hold. This reduces the chance of user attempting to hide oversized files in a capacity-drained carrier. To reveal a hidden file from altered one, simply drag the file, r-click, select ‘Reveal’, enter the password and save the revealed file.
Another free tool is StegaNote that uses RPP (Random Pixel Positioning) and a not-so-common ULTRA crypto algorithm. To counter same password seed resulting in same spread arrangement of data in carrier file, SetgaNote generates a random header using mouse movements and uses it to calculate pixel positions.
If you want to learn how to code steganography, check out few open source implementations like wbStego4.3Open, which provides a wizard and work-flow based environment to perform steganography.
Hiding information has come a long way since the Nazis used micro-dots in the Second World War in which a dot of ‘i’ would contain secret messages. Today, there are lots of enhancements in techniques and new detection mechanisms are coming up.
nizar.ali@gmail.com
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