antistatic

Category: Reversing
Tags: crackme, babyrev
Points: 100 (51 solves)
Author: Retr0id

Challenge

Heisenberg's uncertainty principle also applies to CTF. Please do not observe my crackme, otherwise you may change its behavior!

Author: Retr0id
Attachments: antistatic

Solution

Open in Ghidra and decompile. main does basically nothing but __libc_gnu_init looks interesting. A lot of weird antidebugging stuff going on that I just NOP'd out.

After cleaning up the decompiled C it's a lot easier to see what's going on:

import pwn

elf = pwn.ELF("antistatic")
gnu_hash = elf.read(elf.sym["gnu_hash"], 50)

for j in range(0x13):
    for c in range(256):
        if (c ^ 0x42 + j) & 0xff == gnu_hash[j]:
            print(chr(c), end="")

print()
# union{ct0rs_b3war3}

Original writeup (https://github.com/qxxxb/ctf/tree/master/2021/union_ctf/antistatic).