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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)