BlindSide is an example of the art of steganography - the passing of secret
messages in a form such that one would not suspect the message is being
passed. This is an area of cryptography that is attracting considerable
interest of late. The Blindside utility can hide a file (or files) of any
variety, within an uncompressed Windows Bitmap image (BMP file). The original image and
the encoded image look absolutely identical to the human eye - but when run
back through Blindside, the concealed data can be extracted and secret data
retrieved. For added security you can even scramble your data with a password.
There are other programs in the commerical and freeware streams that can
accomplish tasks similar to this program. Many of these will adjust every
single pixel's LSB (the least significant bit of the pixel), and store
data in these imperfections. This can lead to obvious corruption in the
image - which defeats the secrecy (the main ideal of steganography).
Blindside analyses the colour differentials in the image, and will only
alter pixels that it knows will not be noticeable to the human eye.
The downside is that each image has its own 'capacity' dependent on colour
patterns within it - but the upside is that any data you scramble with
Blindside will most definitely be invisible to the human eye.
What could I use this for?
The possibilities are endless. The beauty of the Blindside system is that
it is a steganographic technique supplemented with a cryptographic algorithm.
This means you can pass messages around without even arousing suspicion that
you are doing so (steganography) - and you can encrypt these messages with
password based encryption such that even if anyone did examine the images,
they would need a password to reveal the secret data (cryptography).
If you were a digital image publisher for instance, you could use
Blindside to embed a license file within your images - containing a
copyright notice. A similar procedure could be applied to images on
a company's web pages.
Blindside is made available free for everyone to use, and can
also be redistributed freely. The only exception is that I would ask to
be contacted prior to any commercial/government use.
Where do I get bitmaps from?
If you are running Windows, then bitmaps are everywhere - you can set them
as your wallpaper or download them from the net.
These have been analysed using Blindside and have a data capacity rating
beside them - so you can see how much data the image will store before
you spend valuable time downloading it!
If you own a scanner or digital camera, you can make your own bitmap files
or failing that try your hand at drawing one?? Blindside tends to work
better with real-life images rather than computer generated ones.
Rendered fractal images however, work well.
How does the encryption process work?
In a computer image, particularly a scanned photograph or digitised picture -
there can be many millions of colors - over 16 billion in some.
It is impossible for any human to discriminate and pick out each of these
colors perfectly... the human eye simply is not accurate enough.
BlindSide takes advantage of this fact, and can create slight inflections
and flaws in the colors of an image - into which secret data or files can
be concealed. To the naked eye, the original image, and the image containing
concealed data are completely identical.
What can I conceal in an image?
Anything you like. Each image has its own capacity limit - which you can
check with BlindSide. However, what you actually store in the image is up
to you. The data could be a poem, a love letter, a sound file, maybe even
a Word document, program or another image altogether! No matter what you
store, the result image will look no different than your original. The only
difference is that you know that when you run it through BlindSide again -
there is a secret file contained inside.
How do I use Blindside?
BlindSide is designed to run from the command line, and so is run at the DOS
prompt from within Windows - or from your shell prompt if you are running
Linux/Solaris or the like.
You can perform 4 actions within BlindSide; Encrypt (hide) files in an image,
Decrypt (restore) files from an image, list files contained in an image, or
check to see how much data you could potentially store in an image.
Encrypting (hiding) data in an image
The following example will add the file 'secret.txt' into image 'source.bmp'.
The output 'sneaky.bmp' is the result.
BSIDE -a source.bmp secret.txt sneaky.bmp
If you wish, you can specify a password too...
BSIDE -a source.bmp secret.txt sneaky.bmp PASSWORD
Now no-one will be able to decrypt the data from the image, unless they
know the password.
Remember that you can add many files into one single image, to create
a Blindside archive. You will be prompted if there is insufficient space
within the image to store any more secret data.
Decrypting (retrieving) data from an image
The following example will extract ALL secret files from 'hidden.bmp'
Note that if the data were scrambled with a password, you
would be prompted to enter it before successful decoding.
BSIDE -x hidden.bmp
If you wanted to extract a particular file (spy.txt) you could use...
BSIDE -x hidden.bmp spy.txt
And if you wanted, you could specify the unlock password on the command line
too - to save time....
BSIDE -x hidden.bmp spy.txt PASSWORD
Of course, this is only used if the data has been password locked.
If you wish to list files within an archive use the -L feature (see later)
Calculating data storage statistics for an image
The following command will check to see how much data can be stored
BSIDE -c mypic.bmp
If mypic.bmp is already a Blindside archive (that is, there are secret
files stored within the image), then you will see data storage statistics
detailing space used, and space free for more secret files.
Listing files stored within a Blindside hidden image
The following command will check the image 'mypic.bmp' for Blindside
concealed files - and list them along with their file sizes.
If the archive is password protected you will be prompted for the
password before the files can be listed.
BSIDE -l mypic.bmp
The Author of this software seems to have abandoned it as of ten years ago, the cited site in the readme file was not up.