SNOW
Section: User Commands (1)
Updated: 28 Dec 1996
Index
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NAME
snow - whitespace steganography program
SYNOPSIS
snow
[
-CQS
] [
-p
passwd
] [
-l
line-len
] [
-f
file
|
-m
message
] [
infile
[
outfile
]]
DESCRIPTION
snow is a program for concealing messages in text files
by appending tabs and spaces on the end of lines, and for
extracting messages from files containing hidden messages.
Tabs and spaces are invisible to most text viewers, hence the
steganographic nature of this encoding scheme.
The data is concealed in the text file by appending sequences of up
to 7 spaces, interspersed with tabs. This usually allows 3 bits
to be stored every 8 columns. An alternative encoding scheme, using
alternating spaces and tabs to represent zeroes and ones, was rejected
because, although it used fewer bytes, it required more columns per bit
(4.5 vs 2.67).
The start of the data is indicated by an appended tab character, which
allows the insertion of mail and news headers without corrupting
the data.
snow provides rudimentary compression, using Huffman tables
optimised for English text. However, if the data is not text, or if
there is a lot of data, the use of the built-in compression is not
recommended, since an external compression program such as
compress or gzip will do a much better job.
Encryption is also provided, using the ICE encryption algorithm
in 1-bit cipher-feedback (CFB) mode. Because of ICE's arbitrary
key size, passwords of any length up to 1170 characters are supported
(since only 7 bits of each character are used, keys up to 1024-bytes
are supported).
If a message string or message file are specified on the command-line,
snow will attempt to conceal the message in the file infile
if specified, or standard input otherwise. The resulting file will be
written to outfile if specified, or standard output if not.
If no message string is provided, snow attempts to extract a
message from the input file. The result is written to the output file
or standard output.
OPTIONS
- -C
-
Compress the data if concealing, or uncompress it if extracting.
- -Q
-
Quiet mode. If not set, the program reports statistics such as
compression percentages and amount of available storage space used.
- -S
-
Report on the approximate amount of space available for hidden
message in the text file. Line length is taken into account, but
other options are ignored.
- -p password
-
If this is set, the data will be encrypted with this password during
concealment, or decrypted during extraction.
- -l line-len
-
When appending whitespace, snow will always produce lines shorter
than this value. By default it is set to 80.
- -f message-file
-
The contents of this file will be concealed in the input text file.
- -m message-string
-
The contents of this string will be concealed in the input text file.
Note that, unless a newline is somehow included in the string, a newline
will not be printed when the message is extracted.
EXAMPLES
The following command will conceal the message "I am lying" in the
file infile, with compression, and encrypted with the password
"hello world". The resulting text will be stored in outfile.
-
snow -C -m "I am lying" -p "hello world" infile outfile
To extract the message, the command would be
-
snow -C -p "hello world" outfile
Note that the resulting message will not be terminated by a newline.
To prevent line wrap if text with concealed whitespace is likely to
be indented by mail or news readers, a line length of 72 or less can
be used.
-
snow -C -l 72 -m "I am lying" infile outfile
The approximate storage capacity of a file can be determined with
the -S option.
-
snow -S -l 72 infile
AUTHOR
This application was written by Matthew Kwan, who can usually be
reached at mkwan@cs.mu.oz.au
SEE ALSO
ice_key_create(3)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- EXAMPLES
-
- AUTHOR
-
- SEE ALSO
-
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