SNOWDROP(1)

NAME

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 water: mark.

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