- Author: LT 'syreal' Jones
- Location: https://play.picoctf.org/practice/challenge/369
- Tags: Reverse Engineering, CoreWars
Due to Instance Launching maintenance, you may access the challenge download file to work offline: Your opponent is the Imp. The source is available here. If you wanted to pit the Imp against himself, you could download the Imp and run your own core wars server. Can you make a CoreWars warrior that wins? Additional details will be available after launching your challenge instance.
I proceeded by first downloading and reviewing the source code used by this CoreWars challenge:
┌──(dna㉿deniers)-[/Ready Gladiator 1]
└─$ cat imp.red
;redcode
;name Imp Ex
;assert 1
mov 0, 1
end
┌──(dna㉿deniers)-[/Ready Gladiator 1]
└─$
I then tried to make an "Imp" that did less work by copying imp.red to imp2.red and using the following code:
;redcode
;name Imp Ex
;assert 1
end
Like with the previous "Ready Gladiator" challenge, my version removes the mov 0, 1 bit of the code and simply does nothing. I started up the instance and was given a means to transmit my version of the "Imp" and the following hint: "You may be able to find a viable warrior in beginner docs." I tried to submit my version to see if it can beat the instance:
┌──(dna㉿deniers)-[/Ready Gladiator 1]
└─$ nc saturn.picoctf.net 57192 < imp2.red
Submit your warrior: (enter 'end' when done)
;redcode
;name Imp Ex
;assert 1
end
Warrior1:
;redcode
;name Imp Ex
;assert 1
end
Warning:
No instructions
Number of warnings: 1
Rounds: 100
Warrior 1 wins: 0
Warrior 2 wins: 100
Ties: 0
Try again. Your warrior (warrior 1) must win at least once.
┌──(dna㉿deniers)-[/Ready Gladiator 1]
└─$
It did not win. So, I tried to pit the original Imp against itself:
┌──(dna㉿deniers)-[/Ready Gladiator 1]
└─$ nc saturn.picoctf.net 57192 < imp.red
Submit your warrior: (enter 'end' when done)
;redcode
;name Imp Ex
;assert 1
mov 0, 1
end
Warrior1:
;redcode
;name Imp Ex
;assert 1
mov 0, 1
end
Rounds: 100
Warrior 1 wins: 0
Warrior 2 wins: 0
Ties: 100
Try again. Your warrior (warrior 1) must win at least once.
┌──(dna㉿deniers)-[/Ready Gladiator 1]
└─$
That did not work either. I did some research as per the advice of the hint, and found a page with some "warrior imps" that I can try against the system [1]. I used the "Mirrored Imp" to beat the system's warrior:
dist equ 4000 ; CORESIZE/2
istep equ 4001 ; CORESIZE/2+1
launch mov imp, imp+dist
spl imp+dist
imp mov.i #0, istep
end
I transmitted it to the system, and ...
┌──(dna㉿deniers)-[/Ready Gladiator 1]
└─$ nc saturn.picoctf.net 57192 < imp2.red
Submit your warrior: (enter 'end' when done)
dist equ 4000 ; CORESIZE/2
istep equ 4001 ; CORESIZE/2+1
launch mov imp, imp+dist
spl imp+dist
imp mov.i #0, istep
end
Warrior1:
dist equ 4000 ; CORESIZE/2
istep equ 4001 ; CORESIZE/2+1
launch mov imp, imp+dist
spl imp+dist
imp mov.i #0, istep
end
Warning:
Missing ';assert'. Warrior may not work with the current setting
Number of warnings: 1
Rounds: 100
Warrior 1 wins: 48
Warrior 2 wins: 0
Ties: 52
You did it!
picoCTF{1mp_1n_7h3_cr055h41r5_f2ba3220}
┌──(dna㉿deniers)-[/Ready Gladiator 1]
└─$
I have no idea what I did, but I know that I got the flag: picoCTF{1mp_1n_7h3_cr055h41r5_f2ba3220}