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CSAW CTF: Reversing 400

October 1, 2012

Binary available at

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 for more.


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