Carrier Files


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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