steganographer -- a program that hides data in other data
Copyleft Javier Lombillo, 2015; all rights reversed


Installation
------------

Run `make`; steganographer should compile on any reasonable system, though the
Makefile will need to be edited if you're using a compiler other than gcc.

The resulting binary is called 'steganographer'.


Terminology
-----------

 - steganography   the art and science of hiding information
 - payload         the data you want to hide
 - camouflage      the data that will be used to hide the payload


Operation
---------

steganographer hides the payload inside of the camouflage using LSB
steganography: each bit in the payload is stored in the least-significant bit
of a byte in the camouflage. Header data is not altered.


***** IMPORTANT NOTES *****

1. When hiding data, the size in bytes of the camouflage (not including header
   data) must be at least 8 times the size of the entire payload. This is an
   arithmetical consequence of using LSB steganography: 8 bits per byte, so 1
   payload byte requires 8 camouflage bytes.

2. When recovering hidden data, the size in bytes of the payload must be provided
   to steganographer. While it is generally possible to store the payload size
   in the header of a camouflage file (e.g., in the reserved bytes of the
   bitmap header), doing so would leave a "smoking gun" in plain sight for
   anyone looking. steganographer was designed to hide data and, as such,
   security trumps convenience.

3. Steganography is obfuscation, not encryption! Anyone with the time and
   inclination can recover the hidden data. For best results, encrypt the
   payload before hiding.

***************************

LSB steganography is particularly well-suited to using raw media files, such as
bitmaps and WAV files, as camouflage. They tend to be large and have
well-structured headers, and the logarithmic nature of human perception means
that changes at the LSB scale are typically imperceptible.

As of version 0.8, steganographer knows how to use the following camouflage:

   * MS Windows bitmap
     - 24-bit color-depth only
     - bitmap byte-padding is respected

   * PCM WAV
     - supports 16-, 24-, or 32-bit WAV files

steganographer was written with extensibility in mind, so adding new
camouflages should not be painful.


Example
-------

You want to hide a 102,484-byte file named 'private.zip' in a bitmap called
'america.bmp', storing the resulting bitmap in a file called 'picture.bmp':

    steganographer -H -b america.bmp -p private.zip -o picture.bmp

You email 'picture.bmp' to your friend, who -- by prior arrangement -- knows
that the hidden file size is 102,484 bytes. She runs

     steganographer -R -b picture.bmp -s 102484 -o private.zip



Javier Lombillo <javier@asymptotic.org>
October 2015