crypto100 keysearch

keysearch.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#define KEYLENGTH	256

int main(int argc, char **argv) {
	FILE* input;
	FILE* output;
	FILE* cipher;
	char k[KEYLENGTH + 1]; //"CENSORED";
	char c, p, o, t = 0;
	int i = 0, j;
	if (argc != 3) {
		printf("USAGE: %s INPUT CIPHER\n", argv[0]);
		return 0;
	}
	
	input = fopen(argv[1], "rb");
	cipher = fopen(argv[2], "rb");
	
	k[0] = 0;
	while ((p = fgetc(input)) != EOF) {
		o = fgetc(cipher) & 0xFF;
		for (j = 0; j < 256; j++){
			c = (p + (j ^ t) + i*i) & 0xff;
			if(o == c)
				break;
		}
		if (o != c){
			printf("Key not found!\n");
			return;
		}
		k[i % KEYLENGTH] = j;
		printf("%s\n", k);
		t = p;
		i++;
		k[i] = 0;
	}
	return 0;
}