PicoCTF Writeup – What Lies Within

Information: 

 

CTF Name: PicoCTF

CTF Challenge: What Lies Within

Challenge Category: Forensics

Challenge Points: 150

PicoCTF 2019.

 

# Challenge Description: 

There’s something in the building. Can you retrieve the flag?

Click on the word building to download the original image.

Writeup 

 
Once we read the description of the challenge we know that the flag should be found in the word building. This word has a link to an image. After downloading the image I opened it:
 
 
By looking at the image nothing seems relevant to help us get the flag. 
 
Considering that the challenge category is Forensics I thought that maybe the information was inside the image, hidden in some way and that by doing a forensic analysis of the image I could retrieve the message (flag). After searching a little bit online, I was able to find out that there is a technique known as Steganography in which a message is hidden inside an image or video without compromising the quality. 
 
It does not hurt to try this idea out! So I searched a little bit more for a tool that would decode messages from images. Meaning that this tool reveals the messages hidden using Steganography either in images or videos.
 
I was able to find this tool:
 

Special thanks to stylesuxx for this amazing tool.

 
After finding this tool I inserted the image and press decode, this was the result:
 
 
 
And the flag is
 
Show flag
picoCTF{h1d1ng_1n_th3_b1t5}

The image source can be found here.

Thank you very much for reading!

Cheers,

MRegra

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