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OUTGUESS(1)            DragonFly General Commands Manual           OUTGUESS(1)

NAME
       outguess - universal steganographic tool

SYNOPSIS
       outguess [ -emt ] [ -r ] [ -k key ] [ -F [+-] ] [ -d datafile ] [ -s
       seed ] [ -i limit ] [ -x maxkeys ] [ -p param ] [ inputfile [
       outputfile ]]

DESCRIPTION
       Outguess is a universal steganographic tool that allows the insertion
       of hidden information into the redundant bits of data sources.  The
       nature of the data source is irrelevant to the core of outguess.  The
       program relies on data specific handlers that will extract redundant
       bits and write them back after modification. Currently only the PPM,
       PNM, and JPEG image formats are supported, although outguess could use
       any kind of data, as long as a handler were provided.

       Outguess uses a generic iterator object to select which bits in the
       data should be modified.  A seed can be used to modify the behavior of
       the iterator. It is embedded in the data along with the rest of the
       message.  By altering the seed, outguess tries to find a sequence of
       bits that minimizes the number of changes in the data that have to be
       made.

       A bias is introduced that favors the modification of bits that were
       extracted from a high value, and tries to avoid the modification of
       bits that were extracted from a low value.

       Additionally, Outguess allows for the hiding of two distinct messages
       in the data, thus providing plausible deniablity.  It keeps track of
       the bits that have been modified previously and locks them.  A
       (23,12,7) Golay code is used for error correction to tolerate
       collisions on locked bits.  Artifical errors are introduced to avoid
       modifying bits that have a high bias.

OPTIONS
       The following command line options, when specified as capital letters,
       indicate options for the second message.

       -F [+-]
              Specifies that OutGuess should preserve statistics based on
              frequency counts.  As a result, no statistical test that is
              based on frequency counts will be able to detect steganographic
              content.  This option is on by default.

       -kK key
              Specify the secret key used to encrypt and hide the message in
              the provided data.

       -dD datafile
              Specify the filename containing a message to be hidden in the
              data.

       -sS seed
              Specify the initial seed the iterator object uses for selecting
              bits in the redundant data. If no upper limit is specified, the
              iterator will use this seed without searching for a more optimal
              embedding.

       -iI limit
              Specify the upper limit for finding an optimal iterator seed.
              The maximum value for the limit is 65535.

       -eE    Use error correction for data encoding and decoding.

       Other options that apply to the general execution of outguess:

       -r     Retrieve a message from a data object.  If this option is not
              specified, outguess will embed messages.

       -x maxkeys
              If the second key does not create an iterator object that is
              successful in embedding the data, the program will derive up to
              specified number of new keys.

       -p param
              Passes a string as parameter to the destination data handler.
              For the JPEG image format, this is the compression quality, it
              can take values between 75 and 100.  The higher the quality the
              more bits to hide a message in the data are available.

       -m     Mark pixels that have been modified.

       -t     Collect statistics about redundant bit usage. Repeated use
              increases output level.

       For embedding messages, you need to specify a source and a destination
       filename.  Outguess determines the data format by the filename
       extension.  If no filenames are specified outguess operates as a filter
       and assumes the PPM data format.

EXAMPLES
       To embed the message hidden.txt into the monkey.jpg image:

              outguess -k "my secret pass phrase" -d hidden.txt monkey.jpg
              out.jpg

       And in the other direction:

              outguess -k "my secret pass phrase" -r out.jpg message.txt

       will retrieve the hidden message from the image.

       If you want to embed a second message, use:

              outguess -k "secret1" -d hide1.txt -E -K "secret2" -D hide2.txt
              monkey.jpg out.jpg

       Outguess will first embed hide1.txt and then hide2.txt on top of it,
       using error correcting codes.  The second message hide2.txt can be
       retrieved with

              outguess -k "secret2" -e -r out.jpg message.txt

SEE ALSO
       cjpeg(1), djpeg(1), pnm(5), stirmark(1)

AUTHOR
       Niels Provos <provos@citi.umich.edu>

                                  1 May 2000                       OUTGUESS(1)