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steghide(1)							   steghide(1)

NAME
       steghide	- a steganography program

SYNOPSIS
       steghide	command	[ arguments ]

DESCRIPTION
       Steghide	 is a steganography program that is able to hide data in vari-
       ous kinds of image- and audio-files. The	color- respectivly sample-fre-
       quencies	 are  not  changed thus	making the embedding resistant against
       first-order statistical 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 paragraph 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 created based on	a  pseudo-ran-
       dom  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 contain the
       correct value by	chance)	are sorted out.	Then a graph-theoretic	match-
       ing  algorithm finds pairs of positions such that exchanging their val-
       ues 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 con-
       tain the	embedded data (but this	is done	by overwriting	them,  not  by
       exchanging them with other pixels).  The	fact that (most	of) the	embed-
       ding 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 (informa-
       tion  about  all	possible algorithms and	modes is displayed by the enc-
       info command).  The checksum is calculated using	the CRC32 algorithm.

COMMANDS
       In this section the commands for	steghide are listed. The  first	 argu-
       ment  must  always  be one of these commands. You can supply additional
       arguments to the	embed, extract and info	commands. The  other  commands
       to not take any arguments.

       embed, --embed
	      Embed secret data	in a cover file	thereby	creating a stego file.

       extract,	--extract
	      Extract secret data from a stego file.

       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	 stan-
	      dard input.

       -cf, --coverfile	filename
	      Specify  the  cover  file	 that  will be used to embed data. The
	      cover file must be in one	of the	following  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	modifications to embed the secret data will be
	      made  directly  to  the cover file without saving	it under a new
	      name.

       -e, --encryption	algo [ mode ] |	mode [ algo ]
	      Specify encryption parameters. This option must be  followed  by
	      one  or two strings that identify	an encryption algorithm	and/or
	      mode. You	can get	the names of all available algorithms and sup-
	      ported modes with	the encinfo command. The default encryption is
	      rijndael-128 (AES) in the	cbc mode.  If you do not want  to  use
	      any encryption, use -e none.

       -z, --compress level
	      Specify  the compression level. The compression level can	be any
	      number in	1...9 where 1 means best speed and 9 means  best  com-
	      pression.

       -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 fol-
       lowing 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
	      directory	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	embed-
       ded message or if you consider using a certain file as cover  file  and
       want to find out	its capacity.

       The  command line steghide info _filename_ will print information about
       _filename_ and then ask you if you would	like to	get information	 about
       data  that is embedded in that file. If you answer with yes you have to
       supply the passphrase that was used to embed the	data in	that file.

       You can also supply the -p, --passphrase	argument (see  below)  to  the
       info  command which has the effect that steghide	will automatically try
       to get information about	the data that  has  been  embedded  using  the
       given passphrase.

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 file-
       name which makes	steghide use standard input or standard	output (which-
       ever  makes  sense). Omitting the corresponding 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  extraction,  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 pic-
       ture.jpg.

       After you have embedded your secret data	as shown above	you  can  send
       the  file  picture.jpg to the person who	should receive the secret mes-
       sage. The receiver has to use steghide in the following way:

	 $ steghide extract -sf	picture.jpg
	 Enter passphrase:
	 wrote extracted data to "secret.txt".

       If the supplied passphrase is correct, the  contents  of	 the  original
       file  secret.txt	 will be extracted from	the stego file picture.jpg and
       saved in	the current directory.

       If you have received a file that	contains embedded data and you want to
       get  some  information about it before extracting it, use the info com-
       mand:

	 $ 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 information 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>

				  13 Oct 2003			   steghide(1)

NAME | SYNOPSIS | DESCRIPTION | COMMANDS | EMBEDDING | EXTRACTING | GETTING INFORMATION ABOUT A COVER/STEGO FILE | COMMON OPTIONS | FILE NAME OPTIONS | EXAMPLES | RETURN VALUE | AUTHOR

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