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)