lsbtools

While experimenting with LSB steganography I wrote several scripts to play with. Eventually this scripts become quite useful so i decided to convert them into a node.js module.

You can also use online version.

NOTE: this is more a playground than a real steganography.

Installing

Install with npm:
``none
npm install lsbtools
`
If you want to use this tools in browser include lsbtools.min.js into your page. Module will be available as lsbTools.

Usage

As any node.js module lsbtools should be requirde before use
`
var lsbTools = require('lsbtools');
`
Thi lib operated on an array of pixels byte data. Each pixel must be presented by for bytes: R, G, B and Alpha. This is because it was at first targeted for pixeldata returned from canvas element with getImageData. In node you can use [pngjs] it also returns image pixels in this 4 byte format.

If applicable, pixels data will be changed in-place. If you want to preserve original pixel data, make a copy before calling lsbTools methods.

lsbTools exposes this methods:

$3

pixels is an array of pixel. options is an object what can contain following properties (shown with defaults)
`js
{
shuffle: true, // spread data across image instead of writing sequentially
matrix: true, // use matrix encoding to minimize changes
mask: true, // mask data with stream of random bytes
key: [1, 2, 3, 4, 5, 6, 7, 8, 9, 0], // array of bytes used as key for shuffling and masking
pm1code: true // use ±1 encoding instead of LSB flip
}
`
Returns Uint8Array with bytes extracted from image.

$3

Opposite to read, writes data bytes into image. Accepts same options object.

$3

Fill LSB plane of image with provided value. 0 or 1.

$3

Change color components to 255 if LSB was set and to 0 if not.

$3

Performs chi-squared attack as described in "Attacks on Steganographic Systems. Breaking the Steganographic Utilities EzStego, Jsteg,Steganos, and S-Toolsand Some Lessons Learned" by Andreas Westfeld and Andreas Pfitzmann

URL to pdf with original paper:

Needs pixels array and width of image. Blends image with a map of test results. Red color for zones with data embedded. Green color for clean zones. If enhance parameter evaluates to true then pixels will be enhanced according to their LSB value.

Returns estimated length of embedded message (in bits).

$3

Performs "RS Steganalysis" attack as described in "Reliable Detection of LSB Steganography in Color and Grayscale Images" by Jessica Fridrich et al.

URL to pdf with original paper:

Needs pixels array and width of image. You also can provide mask in a form of an array, like [1, 0, 1, 0] and width and height (bw and bh) of block what is analyzed with that matrix.

Returns estimated capacity usage (usually from 0 to 1, but can be negative).

$3


Return RC4 cipher initialized from key (array of bytes) as object with following methods:

#### rc4.rc4Rnd()
Return next byte from RC4 keystream.

#### rc4.rc4RndFloat()
Reads four bytes from RC4 keystream and returns real value derived from them. Value in [0,1] range.

CLI tool

If lsbtools module installed globally with npm, then you can use it from command line. Only png images are supported as input.

Here is help output of this tool:

`none
usage:

embed: lsbtools -eb -p password -d message.txt -o secret.png clean.png
extract: lsbtools -xb -p password -d hidden.txt secret.png

options:

-p, --password password for shuffle.
-e, --embed hidde data in image.
-x, --extract extract hidden data from image.
-s, --shuffle embed with shuffle.
-k, --mask mask data.
-m, --matrix use matrix coding.
-1, --plusminus1 use +-1 code instead of bit flip.
-b, --best best settings. Equals to -smM1.
-d, --data data for embedding.
-o, --output file for output.
-t, --test extract data but do not write it to disc.
-C, --chitest perform chi-squared test.
-R, --rstest perform RS Steganalysis.
-a, --enhance enhance LSB plane.
-f, --fill fill LSB plane with 0 or 1.
-h, --help show usage information.
``

License

This code released under MIT license.

[pngjs]: https://www.npmjs.com/package/pngjs