extensions

Challenge Description

We shall begin by using wget <link> to download the file provided.

Running file flag.txt shows that flag.txt is a .png file instead of a .txt file. exiftool also indicates that the file type is PNG.

PicoCTF Hint: How do operating systems know what kind of file it is? (It's not just the ending!

By running hexedit flag.txt, we can also see that the file signature of flag.txt is indeed the file signature of a png file.

Hence, we can run cp flag.txt flag.png to give this file the correct file extension. Opening this file using the GUI allows us to see the flag in plaintext.

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picoCTF{now_you_know_about_extensions}