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NDH CTF 2015 - Cooper Writeup

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NDH 2015 Cooper Writeup
Point = 300
Category = Stegano

“I am not crazy, my mother had me tested.” (Sheldon)

What did Sheldon … huh sorry, Dr. Cooper really mean? (

The tar zip contains a Windows executable, so the first thing I did was opening it in CFF Explorer. Doing so I found a picture of Sheldon … or better say "Dr. Cooper" in resources and a section called .hidden containing a ZIP file.

Sheldon's picture

Within the zip file there was a C++ code project with encrypt and decrypt functions.

> dir Stegano-BMP-master
2013-06-21  05:24 PM               533 decrypt.cpp
2015-04-04  12:10 PM    <DIR>          easybmp
2013-06-21  05:24 PM               768 encrypt.cpp
2013-06-21  05:24 PM                28 main.cpp
2013-06-21  05:24 PM               564 Makefile
2013-06-21  05:24 PM               238
2013-06-21  05:24 PM             2,705 stegano.cpp
2013-06-21  05:24 PM               196 stegano.h
               7 File(s)          5,032 bytes

First thing that strikes the mind is to compile the project and decrypt (extract) the flag from it, and I did, and I FAILED :(

 >decrypt cooper.bmp

Obviously 3 cannot be the flag! (but I did submit it and the server did reject it :)) So I insepected the files more, and I found a PDF file in the EXE’s hex dump. I fixed and opened it and finally found “my precious”!

tha flag

BTW: The PDF is password protected which the reader has to guess :D

Written by MMS