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SYNOPSIS

       steghide command [ arguments ]


DESCRIPTION

       Steghide  is  a steganography program that is able to hide
       data in various  kinds  of  image-  and  audio-files.  The
       color- respectivly sample-frequencies are not changed thus
       making the embedding resistant against first-order statis­
       tical tests.

       Features  include  the  compression  of the embedded data,
       encryption of the embedded data  and  automatic  integrity
       checking  using a checksum. The JPEG, BMP, WAV and AU file
       formats are supported for use as cover file. There are  no
       restrictions on the format of the secret data.

       Steghide uses a graph-theoretic approach to steganography.
       You do not need to know anything about graph theory to use
       steghide  and  you  can safely skip the rest of this para­
       graph if you are not interested in the technical  details.
       The  embedding  algorithm  roughly  works  as  follows: At
       first, the secret data is compressed and encrypted. Then a
       sequence  of  postions of pixels in the cover file is cre­
       ated based on a pseudo-random number generator initialized
       with  the  passphrase (the secret data will be embedded in
       the pixels at these positions). Of these  positions  those
       that  do not need to be changed (because they already con­
       tain the correct value by chance) are sorted out.  Then  a
       graph-theoretic  matching  algorithm  finds pairs of posi­
       tions such that exchanging their values has the effect  of
       embedding  the  corresponding  part of the secret data. If
       the  algorithm  cannot  find  any  more  such  pairs   all
       exchanges  are  actually  performed.   The  pixels  at the
       remaining positions (the positions that are  not  part  of
       such  a  pair)  are  also modified to contain the embedded
       data (but  this  is  done  by  overwriting  them,  not  by
       exchanging  them  with other pixels).  The fact that (most
       of) the embedding  is  done  by  exchanging  pixel  values
       implies  that  the first-order statistics (i.e. the number
       of times a color occurs in the picture)  is  not  changed.
       For  audio  files  the  algorithm is the same, except that
       audio samples are used instead of pixels.

       The default encryption algorithm is Rijndael  with  a  key
       size  of  128 bits (which is AES - the advanced encryption
       standard) in the cipher block chaining mode. If you do not
       trust  this  combination  for whatever reason feel free to
       choose  another  algorithm/mode  combination  (information
       about  all  possible  algorithms and modes is displayed by
       the encinfo command).  The checksum  is  calculated  using
       the CRC32 algorithm.


       info, --info
              Display information about a cover or stego file.

       encinfo, --encinfo
              Display a list of encryption algorithms  and  modes
              that can be used. No arguments required.

       version, --version
              Display  short  version  information.  No arguments
              required.

       license, --license
              Display steghide's license. No arguments  required.

       help, --help
              Display a help screen. No arguments required.



EMBEDDING

       You  should  use  the  embed  command if you want to embed
       secret data in a cover file. The following  arguments  can
       be used with the embed command:


       -ef, --embedfile filename
              Specify  the  file  that will be embedded (the file
              that  contains  the  secret  message).  Note   that
              steghide embeds the original file name in the stego
              file. When extracting data (see below) the  default
              behaviour  is  to  save  the embedded file into the
              current directory under its original name. If  this
              argument is omitted or filename is -, steghide will
              read the secret data from standard input.


       -cf, --coverfile filename
              Specify the cover file that will be used  to  embed
              data.  The cover file must be in one of the follow­
              ing formats: AU, BMP, JPEG or WAV. The  file-format
              will  be  detected  automatically  based  on header
              information (the extension  is  not  relevant).  If
              this argument is omitted or filename is -, steghide
              will read the cover file from standard input.


       -sf, --stegofile filename
              Specify the name for the stego file  that  will  be
              created.  If  this argument is omitted when calling
              steghide with the embed command, then the modifica­
              tions  to  embed  the  secret  data  will  be  made
              directly to the cover file without saving it  under
              Specify  the  compression  level.  The  compression
              level can be any number in 1...9 where 1 means best
              speed and 9 means best compression.


       -Z, --dontcompress
              Do  not  compress  the secret data before embedding
              it.


       -K, --nochecksum
              Do not embed a CRC32 checksum. You can use this  if
              the  secret  data  already  contains  some  type of
              checksum or if you do not want to embed those extra
              32 bits needed for the checksum.


       -N, --dontembedname
              Do  not  embed the file name of the secret file. If
              this option is used, the extractor needs to specify
              a  filename  to  tell  steghide  where to write the
              embedded data.



EXTRACTING

       If you have received a file that contains a  message  that
       has  been  embedded with steghide, use the extract command
       to extract it. The following arguments can  be  used  with
       this command.


       -sf, --stegofile filename
              Specify  the  stego  file  (the  file that contains
              embedded data). If  this  argument  is  omitted  or
              filename is -, steghide will read a stego file from
              standard input.


       -xf, --extractfile filename
              Create a file with the name filename and write  the
              data that is embedded in the stego file to it. This
              option overrides the filename that is embedded  int
              the  stego  file.  If this argument is omitted, the
              embedded data will be saved to the  current  direc­
              tory under its original name.



GETTING INFORMATION ABOUT A COVER/STEGO FILE

       You can use the info command to get some information about
       a cover or stego file  (for  example  the  capacity).  You
       might want to use this if you have received a file and you
       are not sure if it contains an embedded message or if  you



COMMON OPTIONS

       The following options can be used with all commands (where
       it makes sense).


       -p, --passphrase
              Use  the  string  following  this  argument  as the
              passphrase. If your passphrase contains whitespace,
              you  have  to enclose it in quotes, for example: -p
              "a very long passphrase".


       -v, --verbose
              Display detailed information about  the  status  of
              the embedding or extracting process.


       -q, --quiet
              Supress information messages.


       -f, --force
              Always overwrite existing files.



FILE NAME OPTIONS

       All file name arguments (-cf, -ef, -sf, -xf) also accept -
       as a filename which makes steghide use standard  input  or
       standard output (whichever makes sense). Omitting the cor­
       responding file name argument will have the same effect as
       using  -  with  two  exceptions: If -sf is omitted for the
       embed  command,  then  the  modifications  will  be   done
       directly  in the cover file. If -xf is omitted for extrac­
       tion, then the embedded data will be saved under the  file
       name that is embedded in the stego file.  So when you want
       to be sure that standard input/output is used,  use  -  as
       filename.



EXAMPLES

       The basic usage is as follows:

         $ steghide embed -cf picture.jpg -ef secret.txt
         Enter passphrase:
         Re-Enter passphrase:
         embedding "secret.txt" in "picture.jpg"... done

       This  command  will embed the file secret.txt in the cover
       file picture.jpg.

       and you want to  get  some  information  about  it  before
       extracting it, use the info command:

         $ steghide info received_file.wav
         "received_file.wav":
           format: wave audio, PCM encoding
           capacity: 3.5 KB
         Try to get information about embedded data ? (y/n) y
         Enter passphrase:
           embedded file "secret.txt":
             size: 1.6 KB
             encrypted: rijndael-128, cbc
             compressed: yes

       After  printing  some  general information about the stego
       file (format, capacity) you  will  be  asked  if  steghide
       should  try to get information about the embedded data. If
       you answer with yes  you  have  to  supply  a  passphrase.
       Steghide  will  then try to extract the embedded data with
       that passphrase and - if it succeeds - print some informa­
       tion about it.



RETURN VALUE

       Steghide  returns  0 on success and 1 if a failure occured
       and it had to terminate before completion of the requested
       operation.  Warnings  do  not have an effect on the return
       value.



AUTHOR

       Stefan Hetzl <shetzl@chello.at>



                           14 May 2002                steghide(1)

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last change:
October 13, 2003