A Simple XOR Cipher

Encrypter.c

#include <stdio.h>

int main(int argc, char *argv[]) {
	FILE *input, *key, *output;
	int inchar, keychar;
	
	if (argc != 4) {
		printf("Usage: \"%s [input] [key] [output]\"", argv[0]);
		return -1;
	}
	
	if ((input = fopen(argv[1], "rb")) == NULL) {
		printf("Invalid input file.");
		return -1;
	}
	if ((key = fopen(argv[2], "rb")) == NULL) {
		printf("Invalid key file.");
		return -1;
	}
	if ((output = fopen(argv[3], "wb")) == NULL) {
		printf("Invalid output file.");
		return -1;
	}
	
	while ((inchar = fgetc(input)) != EOF) {
		
		if ((keychar = fgetc(key)) == EOF) {
			rewind(key);
		}
		
		fputc(inchar ^ keychar, output);
		
	}
	
	fclose(input);
	fclose(key);
	fclose(output);
	
	return 0;
}