Write-up: Brute me - CTF HoneyCON 2018 (Reversing challenge)

solve_rev4.c

#include <stdio.h>
#include <stdlib.h>

const char xored[] = {0x0D, 0x3C, 0x0F, 0x48, 0x1E, 0x57, 0x30};

int testit(char *key) {
	
	int v6 = 0;
	int v7 = 0;
	int i;
	
	for(i = 0; i < 7; i++) {
		
		v6 += (int)key[i];
		v7 += (int)(xored[i] ^ key[i]);
		
	}
	
	// printf("v6 = %d  |  v7 = %d\n", v6, v7);
	
	if(v6 == 666 && v7 == 569)
		return 1;
	
	else
		return 0;
	
}

char printSolution(char *key) {
	
	int i;
	char result[7];
	
	for(i = 0; i < 7; i++)
		result[i] = key[i] ^ xored[i];
	
	printf("KEY VALIDA (from %s) --> %s\n", key, result);
	
}

void main() {
	
	char key[] = {'D', 'c', 'W', 'x', 0x00, 0x00, 0x00};
	
	int i, j, k;
	
	for(i = 0x21; i < 0x7B; i++) {
		
		for(j = 0x21; j < 0x7B; j++) {
			
			for(k = 0x21; k < 0x7B; k++) {
				
				key[4] = i;
				key[5] = j;
				key[6] = k;
				
				if(testit(key)) {
					
					printSolution(key);	
					
				}
				
				// printf("%s\n", key);
				
			}
			
		}
		
	}
	
}