- [Instructor] Steganography is
a concept related to cryptography,
that you'll need to know to pass the exam.
Steganography is the process of hiding information
within another file, so that it is not visible
to the naked eye.
It is the art of hiding information in plain sight,
and it is a particularly valuable communication secrecy tool
for those who do not want others to know
that they are even communicating in the first place.
One of the most common steganography techniques
involves hiding text within an image file.
Image files are quite large and contain
millions of individual pixels, each of which
is shaded an individual color.
That's the reason that we talk about
the resolution of a photo in terms of megapixels;
a 30 megapixel image has 30 million individual pixels,
little colored dots.
Steganography makes slight modifications to those pixels,
perhaps adjusting the shade of a pixel by one or two tones,
to create a hiding space for other information.
If steganography slightly adjusted the shade
of a few thousand of those 30 million pixels,
you'd never be able to notice the difference in practice.
However, given the right software, someone who knew
the image contained embedded text could retrieve it.
Let's take a look at how this works,
using a software program called Quick Stego.
The first thing I'm going to do here
is open this picture that I have saved on my desktop.
Let me zoom out of this picture
so you can see the whole image,
and you'll notice this is just
an innocent looking picture of some kids on a camping trip.
This is the kind of photo that I might share
with my coworkers after the trip was over,
or I might post it on a website for others to view.
If I go ahead and zoom way in on this file,
let's just scroll down here to an interesting part
that includes some people and zoom right in,
you can start to see, as I zoom in closer and closer,
that the individual pixels in this image
are starting to show up.
There's lots of little tiny colored dots here,
that represent the pixels in this image.
I'm going to zoom back out again,
so we can see the whole thing.
And now what I'd like to do is
embed a file within this image.
Let's go ahead and close this picture out,
and then I'm going to launch the Quick Stego program.
Now, this program is designed to embed text
within those images.
So the first thing I'm going to do is open the image file,
and I'm going to tell it to use the kids camping image,
which then appears on the screen.
Now I'm going to call up the text
that I would like to include in the file.
I'm just going to use the Declaration of Independence
like I did in an earlier video.
I'll open the text file,
choose the Declaration of Independence,
which is now shown here on the screen,
and then I'm going to click the hide text button,
and the message appears down here
that the text message is now hidden within the image.
The next thing I'd like to do is save this image file,
and I'm going to give it a different name,
I'm going to give it the name Kids Camping with secret text.
Obviously, I wouldn't give it
such an obvious name if I wanted to hide this,
but this will help me keep straight
which image is which.
Now I'll go ahead and just clear
the text from the screen, here,
I'm going to exit Quick Stego.
And you'll notice I now have this new file,
Kids Camping with secret text,
hidden on my desktop.
I can go ahead now, and completely delete
the text of the Declaration of Independence.
I'll even empty the recycle bin,
to make it completely go away,
so you know I don't have any tricks up my sleeve.
I'm going to open Quick Stego again,
I'm going to click open image,
and this time I'm going to choose the
Kids camping with secret text image.
And you can see, as soon as I open that,
the file, the Declaration of Independence,
appears on the right side of the screen.
If I exit out of Quick Stego
and open the Kids Camping with secret text
just using Microsoft Paint, and then zoom out here,
you'll see the image appears exactly the same
as the image that I had earlier.
There might be some very tiny changes
to some of the pixels somewhere in this image
but, to the naked eye, this appears like
just an image of some kids on a camping trip.
Little do most observers know
that the entire text of the Declaration of Independence
is hidden within this image.
That's how steganography allows the hiding of text,
and other information, within images and other files.
These images may then be posted on websites,
or in other public locations,
where everyone except the intended recipient
believes that it's just an innocent image,
and they have no idea that it contains secret information.