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>
