.TH SNOWDROP 1 .SH NAME sd-eng, sd-engf, sd-c \- text watermarking and watermark recovery .SH SYNOPSIS .B sd-eng [\fI-6\fP] \fI-i\fP \fBorigfile\fP \fBnewfile\fP \fB"Recipient"\fP [\fB"Comment"\fB] .P .B sd-eng [\fI-6\fP] \fI-e\fP \fBorigfile\fP \fBnewfile\fP .P .B sd-eng [\fI-6\fP] \fI-l\fP .SH DESCRIPTION snowdrop is a stenographic text watermarking and watermark recovery system. It is composed of three programs: .TP .B sd-eng Watermark normal English text. .TP .B sd-engf Watermark fine quality English text, yielding higher quality output but encoding less information. .TP .B sd-c Watermark C code. .P 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. .P The watermark is a md5sum, which is retrievable 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 redundantly in multiple independent channels. .P The three usage modes are adding a watermark, checking for the presence 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. .SH OPTIONS .TP .B -i Inject a watermark into a file. You must pass it the original file, the filename to output the watermarked version to, information about who you intend the watermarked file for, and an optional comment. .TP .B -e Extract a watermark from a file. Needs the original file and the new file that you suspect bears the watermark. .TP .B -l Lists the contents of the watermark database. Each of the three programs will have a different list. .TP .B -6 Enable 64 bit watermarking. The default is a weak 32 bit watermark. .SH ENVIRONMENT .TP .B SD_SYNONYMS This variable can be used to point snowdrop at a customized synonyms file. .SH FILES .TP .B ~/.snowdrop/database Database of watermarked files. .SH "SEE ALSO" .TP .B /usr/share/doc/snowdrop/README.gz Explain snowdrop in more depth, its limitations, and how to write additional watermarking modules for other types of files. .SH AUTHOR Michal Zalewski