121 lines
No EOL
4.8 KiB
JavaScript
121 lines
No EOL
4.8 KiB
JavaScript
/*
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Ox.Image provides a pair of methods, `encode` and `decode`, which can be used
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for <a href="http://en.wikipedia.org/wiki/Steganography">steganography</a>, i.e.
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to add a hidden message to an image.<br><br> The signature of the `encode`
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function is `image.encode(message, deflate, mode, callback)`. `deflate` turns
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deflate-compression on or off, and `mode` determines which bits of the image the
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message will be written to — but for most purposes, the default values
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(`true` and `0`) are fine, so `deflate` and `mode` can be omitted.
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In this example, we demonstrate a valid use case for `deflate` and `mode`: To
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encode an decoy message (a line of text), which will be relatively easy to
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detect, and then the the actual message, (another image, itself containing
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another line of text), which will be harder to detect.
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*/
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'use strict';
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Ox.load('Image', function() {
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var $table = Ox.$('<table>').appendTo(Ox.$('body')),
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$tr,
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text = {
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iceland: 'The first image he told me about '
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+ 'was of three children on a road in Iceland in 1965.',
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vietnam: 'He said for him it was the image of happiness, '
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+ 'and that he had often tried to link it to other images, '
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+ 'but it had never worked.'
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};
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encode(decode);
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/*
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So we first encode two lines text into two images, by writing them bit by
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bit (without compression, `deflate = false`), into the least significant bit
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of each 8-bit RGB value (`mode = 1`). Then we encode one image into the
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other: We take the (deflate-compressed, `deflate = true`) data URL of the
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source image and flip, if needed, the second least significant bit of each
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RGB value of the target image, so that the number of bits set to 1, modulo 2
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(for example: 10101010 -> 0), is the bit we're encoding (`mode = -1`). As
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the least significant bit remains untouched, this will preserve the encoded
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text.
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*/
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function encode(callback) {
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status('Load iceland.png');
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Ox.Image('png/iceland.png', function(iceland) {
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result(Ox.$('<img>').attr({src: iceland.src()}));
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status(
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'Encode the text <i>"' + text.iceland + '"</i> into '
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+ 'the least significant bits of iceland.png'
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);
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iceland.encode(text.iceland, false, 1, function(iceland) {
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result(Ox.$('<img>').attr({src: iceland.src()}));
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status('Load vietnam.png');
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Ox.Image('png/vietnam.png', function(vietnam) {
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result(Ox.$('<img>').attr({src: vietnam.src()}));
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status(
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'Encode the text <i>"' + text.vietnam + '"</i> into'
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+ ' the least significant bits of vietnam.png'
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);
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vietnam.encode(text.vietnam, false, 1, function(vietnam) {
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result(Ox.$('<img>').attr({src: vietnam.src()}));
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status(
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'Encode vietnam.png into iceland.png '
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+ 'by flipping the second least significant bits'
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);
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iceland.encode(vietnam.src(), -1, function(iceland) {
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result(Ox.$('<img>').attr({src: iceland.src()}));
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callback(iceland);
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});
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});
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});
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});
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});
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}
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/*
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Finally, we decode all the data again.
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*/
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function decode(iceland) {
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status('Decode the least signigicant bits of iceland.png');
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iceland.decode(false, 1, function(str) {
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result(str);
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status('Decode all bits of iceland.png');
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iceland.decode(-1, function(src) {
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result(
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src.slice(0, 32) + '<i> ... ['
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+ Ox.formatNumber(src.length - 64)
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+ ' more bytes] ... </i>' + src.slice(-32)
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);
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status('Load as vietnam.png');
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Ox.Image(src, function(image) {
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result(Ox.$('<img>').attr({src: src}));
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status('Decode the least significant bits of vietnam.png');
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image.decode(false, 1, result);
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});
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});
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});
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}
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function status(value) {
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var $td = Ox.$('<td>');
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if (Ox.isString(value)) {
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$td.html(
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value.replace(/(\w+\.png)/g, '<b>$1</b>')
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);
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} else {
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$td.append(value);
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}
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$tr = Ox.$('<tr>').append($td).appendTo($table);
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}
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function result(value) {
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var $td = Ox.$('<td>');
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if (Ox.isString(value)) {
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$td.html(value);
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} else {
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$td.append(value);
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}
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$tr.append($td);
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}
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}); |