Pragyan CTF 2017: Evil Corp (100pts)

By: ChalmersCTF

Challenge Description :

fsociety has launched another attack at Evil Corp. However, Evil Corp has decided to encrypt the .dat file with a CBC cipher. Reports reveal that it is not AES and the key is relatively simple, but the IV might be long. And remember, fsociety and evilcorp are closely linked.

NOTE :- Please enclose the flag in the format pragyanctf{<flag>}.

Hint! Snakes serve the fsociety. Hmmm.
Hint! fscociety and evilcorp are too close, even 16 characters long together. Damn

File : fsociety.dat

Solution:

One of the team mates Told me that he is sure that this is Serpent CBC cihper.

Using this tool: http://serpent.online-domain-tools.com/ with the password fsociety. We got a file that looks like an image but missing the JPG Magic numbers. Adding the magic numbers using hexeditor we could see the image.

Note: image might not open or show in github :P

flag is pragyanctf{HelloFriend}