CrossCTF_2017:

Category: Reverse Engineering Points: 25 Description:

Can you unravel the flag? File here

Write-up

Loading it up in something like Hopper, we get a pretty good glimpse of what we need to do, so we have to find the payload. Firstly, bastion leads us to another pointer where we find our real payload, save for one character, which if we look further in ASM, we find 0x69 in crackme(). Therefore, the full payload is 692A583744377420661D5C32066A132617791E41355D6E314236027647245953, knowing that, we can xor every byte of the payload with the next byte to give us the flag.

0x69 ^ 0x2a = C
0x2a ^ 0x58 = r
...

Therefore, the flag is CrossCTF{An4ly51ng_th3_st4t1c}.

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