A tool for steghide (see also the Github repo) to embed large files in a collection of files steganographically.
While the steghide tool can nicely embed a single "embed" file in one other "cover" file as long as the "cover" file's capacity is large enough, "embed" files larger than the capacity of a single "cover" file cannot be handled by steghide. The steg script presented here aims at solving this problem by allowing you to specify a collection of "cover" files whose cumulative capacity must suffice to embed the "embed" file into them. Then, the capacity of each single "cover" file is determined, and with a certain safety margin (currently using 80% of the capacity listed by steghide info <cover-file>) the "embed" file is encoded in chunks into the "cover" files. If the aggregated "cover" file capacity does not suffice, the command will exit with code 1. Note that if the capacity suffices, most likely not all "cover" files were really used. The standard error output will tell the files used.
By default, JPEG files in the current directory and its subdirectories (recursively) are used, but finding the cover files can be controlled by specifying a different directory (-d) and different file extensions (-f). Of course, only files acceptable as cover files for steghide must be specified (JPEG, BMP, WAV, AU).
Example:
steg -p mysecretpassword IMG_1234.JPG
This will find all JPEG/jpeg/JPG/jpg files in the current folder and all its subfolders as "cover" files and will embed the file IMG_1234.JPG in as many of those "cover" files as are required based on their capacity. To extract from the same set of "cover" files, use
steg -x -p mysecretpassword IMG_1234.JPG.copy
Trying this you should notice that the .copy file's contents will equal those of the original file.
If you don't have it already, install the steghide tool on your distribution, e.g., using
sudo apt-get install steghide
Clone the [email protected]:axeluhl/steg repo, e.g., to your /usr/local/src folder, like this:
git clone [email protected]:axeluhl/steg.git
Link the script to your /usr/local/bin folder, like this:
sudo ln -s /usr/local/src/steg/steg /usr/local/bin
Link the man page to your /usr/local/man folder, like this:
sudo mkdir -p /usr/local/man/man1
sudo ln -s /usr/local/src/steg/steg.1.gz /usr/local/man/man1
You can use the steg bash script as follows:
steg [ -x ] [ -d <directory-with-cover-files> ] [ -p <passphrase> ] [ -e <encryption-algorithm> ] [ -f <comma-separated-list-of-file-extensions> ] [ -h ] [ <embed-file> ]
If -x is provided, extracts a file from the cover files; otherwise, the or standard input will be embedded into the cover files in place, modifying one or more of the cover files.
To see the list of available encryption algorithms call steghide encinfo.
If a directory is provided using -d, all JPEG/jpeg/JPG/jpg files are listed and sorted by path and the files will be used in that order as cover files to extract or embed the content of the embed file. If no directory is provided with -d, the cover files will be searched recursively, starting from the current directory.
If no <embed-file> is provided, the standard input will be embedded, or extraction will go to standard output, respectively.
If no passphrase is provided using the -p parameter, the tool will prompt for one.
To override the default file extension list "jpeg,jpg", use the -f parameter. File name matching is case-insensitive, so "-f wav" will match all .wav and .WAV (and even .WaV) files.
Progress output goes to standard error.
The program exits with code 0 in case all went well; 1 in case there was input left that did not fit into the cover file(s), and 2 if this usage hint was requested. The tool exits with code 4 in case an unknown option was found, and with 5 in case the confirmation password did not match the original embed password.
Request this usage hint by invoking with -h or without any arguments.
The tool comes with a man page. Writing man pages with groff is nothing I felt worth learning for this little
tool, so I preferred to use pandoc for this task. Find the man page source in steg.1.md. The man page
steg.1.gz can be built from the MarkDown document using the little makeman.sh script. Note a funny
glitch in the toolchain: if your text happens to produce a groff document (steg.1) that accidentally
contains a payload text snippet starting with a "." at the beginning of a line, groff will interpret this
as a command. It took me a while to figure out why ".wav" wouldn't show properly...