Ready Gladiator 1

Author: LT 'syreal' Jones | 200 points

Description

Can you make a CoreWars warrior that wins?

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 connect to the CoreWars server like this:

nc saturn.picoctf.net ***** < imp.red

To get the flag, you must beat the Imp at least once out of the many rounds.

Solution

We are given the same challenge as Ready Gladiator 0, but instead of losing we must win against the Imp.

If you read my writeup on Ready Gladiator 0, I hyperlinked a very useful site detailing how CoreWare works and different warriors you can use. The Imp is the most basic warrior, that can be quickly defeated by the Dwarf:

;redcode
;name Dwarf
;assert 1
add #4, 3
mov 2, @2
jmp -2
dat #0, #0

The goal of the Dwarf is to 'bomb' the core with the DAT instruction. Note that # is used for immediate addressing (actual number values) and @ is used for indirect addressing. The @2 in the second instruction refers to the B-field in the DAT instruction.

ADD #4, 3        ; execution begins here
MOV 2, @2
JMP -2
DAT #0, #0

ADD #4, 3
MOV 2, @2        ; next instruction
JMP -2
DAT #0, #4       

ADD #4, 3
MOV 2, @2  ;  --.
JMP -2     ;    | +2
DAT #0, #4 ; <--' --. The B-field of the MOV points here.
...                 |
...                 | +4
...                 |
DAT #0, #4 ; <------' The B-field of the DAT points here.

The Dwarf will keep dropping DATs every 4 instructions until it has looped around the core.

I very much encourage reading the beginners guide, as they explain it much better than I can.

Flag

The flag is picoCTF{1mp_1n_7h3_cr055h41r5_441be1fc}