Pragyan CTF 2017: Answer to Everything (50pts)

2017-03-05

1 minute read

Challenge Description :

Shal has got a binary. It contains the name of a wise man and his flag. He is unable to solve it.

Submit the flag to unlock the secrets of the universe.

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

Hint! Sometimes, the best place to hide is plain sight.
Hint! SHAl didn't try one thing, which is what he is.

File : main.exe

Solution:

I started by firing up the IDA to analyze the binary after running file which told me its an ELF64 binary. After looking fast at the disassembly I could see that it first asks for an input (a number) then call a function not_the_flag()

main

The function looked like this:

fun

We tried to submit the flag as pragyanctf{kdudpeh} but it did not work. Doing some ROT revealed the key “harambe”. Looking at the released hints we realized we should use the SHA1 representation of the word. And we got the flag. pragyanctf{31a0d851ea10ad886ad4e99ed05892de06998ab9}