<h1>What is steganography?</h1>
<p>Rough description: Steganography consists in hiding a message in a way that only the sender and receiver will know about its existence. Offering security by obscuring. The information is hidden in a container or vessel. The word are of Greek origin <em>steganos</em>, that means <strong>hidden</strong>; and <em>graphos</em>, <strong>writing</strong>.</p>
<p>Every time it is usually misconsidered a variety of <strong>cryptography</strong>, but this last consist in ciphering or encoding a message. An observer looking at that would say: "Yeah, OBVIOUSLY there's a secret message there". In steganography, the message is hidden in plain sight, invisible to the eye that does not know about it.</p>
<p>Now the example:</p>
<p><em>Zup big brother! I am sending you one of the pictures I took at this vacations. so that you may die of envy AHAHAHAAHAH!. I also uploaded it to whateversitetosharepictures.com so that you may re-download it in case that you delete it in a rage attack! AHAHAHA XOXOXOX"</em></p>
<p>https://s3.postimg.org/3mg9grvnn/example.jpg</p>
<p><em>One of the images: The image sent with the message.</em></p>
<p>https://s3.postimg.org/mstgjyc5f/example2.jpg</p>
<p><em>Another image: The image at the picture sharing site.</em></p>
<p>Really? Since we are talking about steganography, you already may guess they are not the same.</p>
<p>https://s3.postimg.org/bdwzfbzsz/compare.jpg</p>
<p>Get your photo editor. If you take both pictures, and place them side to side, they look like so anyways... Anyone looking at them would not be able to tell the difference. But there's...</p>
<p>Do an overlapping and run a "difference" filter in that advanced photo editor, we find a small spot that differs.</p>
<p>https://s9.postimg.org/6esto6x0f/zoom.jpg</p>
<p>If we take the filter off after selecting the pixels that are different and get this:</p>
<p>https://s9.postimg.org/nqokvw13z/exposed.jpg</p>
<p>Do they mean something? Yes. They are a gray-scale line of pixels, their codes are: 115 116 101 101 109, "steem" in ASCII (ALT+keypad, keyboard codes). Even if you FOUND the difference, you still have to know you've to disable the difference filter off, before getting the correct colors. Hide in plain sight.</p>
<h1>Why?</h1>
<p>The writer, Peter Wayner said that "an enemy can only control your information, if he can find it" and, it is not hard to find ourselves, today (specially with internet), in situations that we wish that our privacy is not breached, where compromising data could end at the worst possible hands.</p>
<p>Having a lot of uses in private communication, it is also used for watermarking data, and prove one's authory (photographer's you should ALL know this), track and identify documentation (someone in your company is leaking data, or selling it to the competency? Give each employee a piece of data with a unique mark... wait for it to go public, read the mark: find out who it was).</p>
<p>In this day's networks are flooded with multimedia data (sound, images and videos), allowing us to hide information nearly everywhere (yes, steganography does not only apply to photos, you can do it with audio, andvideos too!).&nbsp;</p>
<h1>Physical Steganography</h1>
<p>Since when do we use it? The first mention to steganography comes from 440 b.c., when Herodotus mentions how messages were hidden by being tattooed into slaves' heads, then they waited for the hair to grow, and sent them wherever the message was destined to go to. Many other ways of doing such thing have been used after that: Invisible ink, is a nice example. Who didn't write a message on paper with lemon juice or milk, to later reveal it with the flame of a candle?</p>
<h1>Digital Steganography</h1>
<p>There's a nearly an infinite amount of ways of hiding data in this modern era:</p>
<ul>
<li>
<p>Replace "noise" in a file (image or sound).</p>
</li>
<li>
<p>Use certain pixels in an image, or specific seconds in an audio.</p>
</li>
<li>
<p>Using another character frequency in a cipher (as in, use the Spanish character frequency, but write in English; that misleads the deciphering into totally wrong characters).</p>
</li>
<li>
<p>Emulate the structure of a text, for example, a to-do list.</p>
</li>
<li>
<p>Replace random data with REAL data.</p>
</li>
<li>
<p>Add information after the EOF (End of file) not affecting how it works.</p>
</li>
</ul>
<p>As you may see, the objective is to camouflage data in a way either human or machine can ever tell the difference of a steganographed container/vessel from an empty vessel. Add into the mix, putting more techniques into the game (as the ASCII characters of the example).</p>
<h1>Weakness</h1>
<p>Depending on the technique, some data can be harder or easier to find (a small image with changed pixels is rather... obvious).<br />The length of the message is of inverse proportion to the detectability.<br />Some format changes are rather... obvious (A txt file that says "hi" and occupies 4Gb of space... HAS hidden data).</p>
<h1>Water Marks</h1>
<p>Water marks is invisible data that is hiding at things like cloth, tags, bills and packaging, without altering them (in a serious way)... Not those things some "photographers" paste on top of their works, totally ruining the image. They are very useful for specific tasks:</p>
<ul>
<ul>
<li>
<p>Monitor transmissions: Identify TV shows, music, files (yes people, that is what Sony uses).</p>
</li>
<li>
<p>Identify an author's work (you'll see an example in a few... :D ).</p>
</li>
<li>
<p>Data tracking, as I previously mentioned in the supposed company leak.</p>
</li>
<li>
<p>Include a digital signature.</p>
</li>
<li>
<p>Copy control, certain Bills cannot be scanned (so I've been told; but friends mentioned that a black image returns when trying to make a full scan of a 100 dollar bill... Someone tell me, please).</p>
</li>
<li>
<p>Device control, items that activate or perform a task when they detect they are in the proximity of a certain multimedia (a barney doll that starts dancing, as soon as it detects the TV show's/song watermark).<br /><br /></p>
</li>
</ul>
</ul>
<p>The list of possibilities is endless</p>
<p>You just read a steganographed message, and didn't notice.</p> <strong>First character of every paragraph.</strong>