CSAW CTF: Reversing 400
Binary available at http://repo.shell-storm.org/CTF/CSAW-2012/Reversing/400/.
We are given an ELF binary and I wasn’t very sure I could solve this since I have not played with ELF much. It was an easy challenge though-I thought Reversing 300 was slightly more difficult.
On executing, the program prints an encrypted key and instantly, I realize it can be solved by adopting the same approach as reversing 100. Just modify the call to encrypt to call decrypt and you get the key:
Encrypted Key: csawissohard__:(
I won’t get into details as to how I patched it: used a combination of IDA and hexedit to do so(yeah I’ve a long way to go in reversing).
PS: Eindbazen has a much more elegant solution than mine. Visit http://eindbazen.net/2012/09/csaw-2012-reversing-400/ for more.