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)