Logo? Gone. Hotel? Trivago.

Briefing:

In case you didn't notice, our logo has been compromised... And unfortunately, we have a pretty good idea of who did it. They're really just trying to get revenge on the money we rightfully stole back. Our team thinks that they've hidden a message in this compromised black and white image, so can you try to uncover it?

First, let’s take a close look at the picture.

Sneaky hacker groups have compromised our logo...

Just an ordinary image with lots of blank space… or is it?

Remember, this is a CTF challenge, and a lot of sneaky stuff can be going on in that blank space.

If you zoom in and make your screen really bright, you might spot something funny in the bottom right corner.

Can you see it? 👁👄👁

1. Let’s dump this into an image editor. (We’ll use GIMP for demonstration, but feel free to use your favorite tool.)

2. We can separate different colors using the Bucket Fill tool-- just remember to lower the threshold so that it doesn’t fill everything!

And we get the flag: BET_U_CANT_SEE_ME

Note: sometimes the difference will be so subtle, that you can’t spot the flag with even the keenest eye, which brings us to...

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Alternative solution: the LSB approach

LSB stands for Least Significant Bit, and it’s commonly used for digital steganography.

• The idea is that if we change each pixel’s color by just a little Bit, the difference would be undetectable by human eyes, and we can hide secret messages with this trick.

❗❔For more, look up LSB steganography.❗❔

Actually doing the challenge...

We’ll use this online image steganography tool: https://georgeom.net/StegOnline/

1. Let’s upload the image and check LSB half.

And... here we go!

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Of course, there is more than these two ways to do it. Did you use a different method or tool? Feel free to share!