SNOW/stegsnow
SNOW (Steganographic Nature Of Whitespace) (also known as stegsnow) encodes messages in ASCII files using whitespace at the end of lines.
Has options to compress and/or encrypt the message using the ICE encryption algorithm.
Prior to 22 November 1998 the DOS version was not compatible with other platforms
To show the beginning of a message, a tab is added immediately after the text on the first line where it will fit. This prevents the insertion of mail and news headers containing trailing spaces from corrupting the message, since a trailing tab must be found before extraction begins.
Data is written 3 bits at a time, coding for 0 to 7 spaces. Any messages not a multiple of 3 bits will be padded by zeroes. During extraction, an extra one or two bits at the end will be ignored (fortunately there are no two-bit Huffman codes to confuse things).
An alternative scheme was considered, where bits were written one at a time as either a space or a tab. Although this scheme adds fewer characters per bit (1 vs 1.5), it requires more columns per bit (4.5 vs 2.67), and column space is the limiting factor.
Tabs are used to separate the blocks of spaces. Thus 3 bits are usually coded in 8 columns of text, and given that the default line length is 80 characters, this allows 30 bits to be stored on empty lines. A tab is not appended to the end of a line unless the last 3 bits coded to zero spaces, in which case it is needed to show some bits are actually there.
If a message will not fit into the available text, empty lines will be appended and used to contain the overflow. A warning message will also be produced, since this affects the look of the original text.
