| A carrier file is a file that is used by wbStego4
to hide your data. Currently four types of carrier files are
supported. Depending on the type, there are some guidelines
to follow. |
Bitmap images
The most important criteria is the color depth (how many bit per
pixel define the color value). Bitmaps with the following color
depths are accepted:
- 4 bit = 16 colors (or 16 gray scales)
- 8 bit = 256 colors (or 256 gray scales)
- 24 bit = 16.777.216 colors
In general can be said: The more colors, the higher the security.
Bitmaps with very large areas in one color should be avoided. Depending
on the color depth bitmaps can take the following amount of hidden
data (ratio size of bitmap in byte : size of hidden data)
- 4 bit = 16 colors: 4 : 1
- 8 bit = 256 colors: 8 : 1
- 24 bit = 16 777 216 colors: 8 : 1
NOTE: Manipulated bitmaps cannot be converted into any other graphic
format because the data hidden in the file could be lost. Formats
offering no or lossless compression (e.g. PCX) can be used, but
the color depth may not be changed. Formats using other compression
methods (e.g. JPEG) may not be used. To reduce the size of the carrier
file, which is very important for online transmission, use a compression
utility (e.g. ARZ, LZH, PKZIP, WinZip), because they work lossless.
Text files
wbStego4
is able to process as well ASCII (DOS) as ANSI (Windows) text files
(*.TXT). wbStego4
offers two different methods for encoding data in text files:
- Standard method: The file size remains unchanged. When importing
manipulated carrier files into word processors (especially under
Windows) there can appear special characters in the text.
- Compatible method: The file is being increased. There are no
changes visible when a manipulated carrier file is imported into
other applications.
The capacity of text files to take hidden data depends very much
on the file's content but can be estimated as follows (in byte):
- Standard method: number of words / 8
- Compatible method: number of lines
HTML files
HTML files are treated as text files using the compatible method.
Adobe PDF
files
There are no limitations when using PDF files. The manipulation
of the file is not visible when viewing the file with Adobe™ Acrobat
or any other PDF viewer. Hiding data in a PDF file will increase
its filesize. There are no general rules for the amount of data
a PDF file can take, but the number is decreased by numerous and
large embedded objects.
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