README.md

Not Slick

Challenge:

My friend always messes with PNGs.... what did he do this time?

Solution:

All we have a is a broken PNG.

Running file doesn't give us much:

$ file notslick.png
notslick.png: data

Which isn't surprising, the file signature doesn't seem to match anything:

$ xxd notslick.png | head
00000000: 8260 42ae 444e 4549 0000 0000 2b2c edb5  .`B.DNEI....+,..
...

But if we run a Google search for B.DNEI, we find some other CTF challenges that indicate that this is actually a reversed PNG.

Sure enough, we can see the telltale indicator of a PNG at the end of the file:

$ xxd notslick.png | tail
...
00018c80: 8007 0000 5244 4849 0d00 0000 0a1a 0a0d  ....RDHI........
00018c90: 474e 5089                                GNP.

Repurposing a script borrowed from this CTF write-up, we can repair our PNG:

That gives us our flag: UMDCTF-{abs01ute1y_r3v3r53d}.