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Avoid a race between fopen(3) and fchmod(2).  Use umask(2) and
unlink(2) and fopen(3) to prevent an attacker to open an old file
with wrong permissions before the secret is written into it.  This
also guarantees that a new file with correct permissions is created.
Without fchmod(2) "fattr" can be removed from pledge.
with and OK deraadt@

/*	$OpenBSD: x99token.c,v 1.12 2015/10/15 19:30:03 bluhm Exp $	*/

/*
 * X9.9 calculator
 * This software is provided AS IS with no express or implied warranty
 * October 1995, Paul Borman <prb@krystal.com>
 *
 * Donated to the Public Domain by Paul Borman
 */

#include <sys/stat.h>

#include <ctype.h>
#include <err.h>
#include <pwd.h>
#include <readpassphrase.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <limits.h>
#include <openssl/des.h>

#define	KEYFILE		".keyfile.des"
#define	HEXDIGITS	"0123456789abcdef"
#define	DECDIGITS	"0123456789012345"

void predict(DES_key_schedule, const char *, int);

char *digits = HEXDIGITS;
extern char *__progname;

int
main(int argc, char **argv)
{
	int i;
	char buf[256];
	DES_key_schedule ks;
	DES_cblock key;
	char _keyfile[PATH_MAX];
	char *keyfile = 0;
	FILE *fp;
	int init = 0;
	int hex = 1;
	int cnt = 1;
	unsigned int pin;
	struct passwd *pwd;

	if (pledge("stdio rpath wpath cpath getpw tty", NULL) == -1)
		err(1, "pledge");

	while ((i = getopt(argc, argv, "dk:in:")) != -1) {
		switch (i) {
		case 'k':
			keyfile = optarg;
			break;
		case 'i':
			init = 1;
			break;
		case 'd':
			hex = 0;
			break;
		case 'n':
			cnt = atoi(optarg);
			if (cnt <= 0)
				err(1, "invalid count: %s", optarg);
			break;
		default:
			fprintf(stderr,
			    "usage: %s [-d] [-k keyfile] [-n count]\n"
			    "       %s -i [-k keyfile]\n",
			    __progname, __progname);
			exit(1);
		}
	}

	if (!keyfile) {
		if ((pwd = getpwuid(getuid())) == NULL) {
			fprintf(stderr, "Say, just who are you, anyhow?\n");
			exit(1);
		}
		snprintf(_keyfile, sizeof(_keyfile), "%s/%s", pwd->pw_dir,
		    KEYFILE);
		keyfile = _keyfile;
	}

	if (init)
		readpassphrase("Enter Key: ", buf, sizeof(buf), 0);
	else if ((fp = fopen(keyfile, "r")) == NULL)
		err(1, "unable to open %s", keyfile);
	else {
		if (fgets(buf, sizeof(buf), fp) == NULL) {
			fprintf(stderr, "No key in %s\n", keyfile);
			exit(1);
		}
		fclose(fp);
	}

	memset(key, 0, sizeof(key));
	if (init && buf[3] == ' ') {
		char *b = buf;
		/* Assume octal input */
		for (i = 0; i < 8; ++i) {
			if (!*b)
				fprintf(stderr, "%s: invalid key\n", buf);
			while (isdigit((unsigned char)*b))
				key[i] = key[i] << 3 | (*b++ - '0');
			while (*b && !isdigit((unsigned char)*b))
				++b;
		}
	} else {
		for (i = 0; i < 16; ++i) {
			int d;

			if (islower((unsigned char)buf[i]))
				buf[i] = toupper((unsigned char)buf[i]);
			if (buf[i] >= '0' && buf[i] <= '9')
				d = buf[i] - '0';
			else if (buf[i] >= 'A' && buf[i] <= 'F')
				d = buf[i] - 'A' + 10;
			else {
				fprintf(stderr, "invalid key: %s\n", buf);
				exit(1);
			}
			key[i>>1] |= d << ((i & 1) ? 0 : 4);
		}
	}

	/* XXX - should warn on non-space or non-digit */
	readpassphrase("Enter Pin: ", buf, sizeof(buf), 0);
	for (i = 0, pin = 0; buf[i] && buf[i] != '\n'; ++i)
		if (isdigit((unsigned char)buf[i]))
			pin = pin * 16 + buf[i] - '0' + 1;

	if ((pin & 0xffff0000) == 0)
		pin |= pin << 16;

	for (i = 0; i < 8; ++i)
		key[0] ^= (pin >> ((i * 7) % 26)) & 0x7f;

	if (init) {
		umask(S_IRWXG | S_IRWXO);
		unlink(keyfile);
		if ((fp = fopen(keyfile, "w")) == NULL)
			err(1, "could not open %s for writing", keyfile);
		for (i = 0; i < 8; ++i) {
			fprintf(fp, "%c", digits[(key[i]>>4)&0xf]);
			fprintf(fp, "%c", digits[(key[i]>>0)&0xf]);
		}
		fputc('\n', fp);
		fclose(fp);
		exit(0);
	}

	DES_fixup_key_parity(&key);
	DES_key_sched(&key, &ks);

	buf[0] = '\0';
	readpassphrase("Enter challenge: ", buf, sizeof(buf), RPP_ECHO_ON);
	if (buf[0] == '\0')
		exit(0);

	for (i = 0; i < 8; ++i)
		if (buf[i] == '\n')
			buf[i] = '\0';

	if (!hex)
		digits = DECDIGITS;

	predict(ks, buf, cnt);

	memset(&ks, 0, sizeof(ks));
	memset(buf, 0, sizeof(buf));

	exit(0);
}

void
predict(DES_key_schedule ks, const char *chal, int cnt)
{
	int i;
	DES_cblock cb;

	memcpy(&cb, chal, sizeof(cb));
	while (cnt-- > 0) {
		printf("%.8s: ", (char *)cb);
		DES_ecb_encrypt(&cb, &cb, &ks, DES_ENCRYPT);
		for (i = 0; i < 4; ++i) {
			printf("%c", digits[(cb[i]>>4) & 0xf]);
			printf("%c", digits[(cb[i]>>0) & 0xf]);
		}
		putchar('\n');
		for (i = 0; i < 8; ++i) {
			if ((cb[i] &= 0xf) > 9)
				cb[i] -= 10;
			cb[i] |= 0x30;
		}
	}
	memset(&cb, 0, sizeof(cb));
}