picoCTF 2019 What Lies Within Writeup

What Lies Within is a forensics puzzle worth 150 points.

The description of this puzzle:

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

An image buildings.png is provided, which shows a picture of a building:


First, I tried using exiftool and just looking around at the picture. This is likely a steganography challenge based on it being in the Forensics category and the puzzle being an image. Usually for steganography challenges, I start by simply trying a bunch of known decoders against it.

In this instance, I got a hit with zsteg:

Solved with zsteg.

I should really sit down one day and make a list of decoders and what kinds of files they work on, and script something out to automate these easier challenges.

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