sd-eng, sd-engf, sd-c - text watermarking and watermark recovery

sd-eng [-6] -i origfile newfile " Recipient" [" Comment" ]

sd-eng [-6] -e origfile newfile

sd-eng [-6] -l

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 independant 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.

-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 waterarking. The default is a weak 32 bit watermark.

SD_SYNONYMS

This variable can be used to point snowdrop at a customized synonyms file.

~/.snowdrop/database

Database of watermarked files.

/usr/share/snowdrop/README

Explain snowdrop in more depth, its limitations, and how to write additional watermarking modules for other tpyes of files.

Michal Zalewski <lcamtuf@coredump.cx>