NAME¶
sd-eng, sd-engf, sd-c - text watermarking and watermark recovery
SYNOPSIS¶
sd-eng [-6] -i origfile newfile
"Recipient" [ "Comment"]
sd-eng [-6] -e origfile newfile
sd-eng [-6] -l
DESCRIPTION¶
snowdrop is a stenographic text watermarking and watermark recovery system. It
is composed of three programs:
- sd-eng
- Watermark normal English text.
- sd-engf
- Watermark fine quality English text, yeilding higher
quality output but encoding less information.
- sd-c
- Watermark C code.
The three programs operate similarly, with the same parameters and usage. The
watermark is encoded in using a number of techniques, such as whitespace
reformatting, typo insertation, word substitutions, punctuation changes, and
for C code, logic reordering, variable name mangling, etc.
The watermark is a md5sum, which is retreivable from as little as 5 or 10 lines
of the watermarked document. Even large changes to a medium sized document
should not obscure the watermark, as it is stored redundently in multiple
independent channels.
The three usage modes are adding a watermark, checking for the presense of a
watermark, and listing the contents of your database of watermarks. Note that
to later check a watermark, you must retain a copy of the original,
un-watermarked file.
OPTIONS¶
- -i
- Inject a watermark into a file. You must pass it the
original file, the filename to output the watwrmarked version to,
information about who you intend the watermarked file for, and an optional
comment.
- -e
- Extract a watermark from a file. Needs the original file
and the new file that you suspect bears the watermark.
- -l
- Lists the contents of the watermark database. Each of the
three programs will have a different list.
- -6
- Enable 64 bit watermarking. The default is a weak 32 bit
watermark.
ENVIRONMENT¶
- SD_SYNONYMS
- This variable can be used to point snowdrop at a customized
synonyms file.
FILES¶
- ~/.snowdrop/database
- Database of watermarked files.
SEE ALSO¶
- /usr/share/snowdrop/README
- Explain snowdrop in more depth, its limitations, and how to
write additional watermarking modules for other tpyes of files.
AUTHOR¶
Michal Zalewski <lcamtuf@coredump.cx>
