/*-
 * Copyright (c) 2012-2013 Universitetet i Oslo
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * Author: Dag-Erling Smørgrav <des@des.no>
 * Sponsor: the University of Oslo
 *
 * $Cryb$
 */

#include "cryb/impl.h"

#include <stdint.h>
#include <string.h>

#include <cryb/sha1.h>
#include <cryb/hmac.h>
#include <cryb/oath.h>

#define StToNum(St) (St)

static uint32_t
DT(const uint8_t *String)
{
	uint8_t OffsetBits;
	int Offset;
	uint32_t P;

	OffsetBits = String[19] & 0x0f;
	Offset = StToNum(OffsetBits);
	P = (uint32_t)String[Offset + 0] << 24 |
	    (uint32_t)String[Offset + 1] << 16 |
	    (uint32_t)String[Offset + 2] << 8 |
	    (uint32_t)String[Offset + 3];
	return (P & 0x7fffffffUL);
}

unsigned int
oath_hotp(const uint8_t *K, size_t Klen, uint64_t seq, unsigned int Digit)
{
	hmac_ctx ctx;
	uint8_t C[8];
	uint8_t HS[20];
	uint32_t Sbits, Snum;
	unsigned int mod, D;

	for (int i = 7; i >= 0; --i) {
		C[i] = seq & 0xff;
		seq >>= 8;
	}

	/* HS = HMAC-SHA-1(K,C) */
	hmac_init(&ctx, K, Klen);
	hmac_update(&ctx, (const uint8_t *)&C, sizeof C);
	hmac_final(&ctx, HS);

	Sbits = DT(HS);
	Snum = StToNum(Sbits);
	for (mod = 1; Digit > 0; --Digit)
		mod *= 10;
	D = Snum % mod;
	return (D);
}

/*
 * Computes the current code for the given key and advances the counter.
 */
unsigned int
oath_hotp_current(struct oath_key *k)
{
	unsigned int code;

	if (k == NULL)
		return (-1);
	if (k->mode != om_hotp)
		return (-1);
	if (k->counter == UINT64_MAX)
		return (-1);
	code = oath_hotp(k->key, k->keylen, k->counter, k->digits);
	k->counter += 1;
	return (code);
}

/*
 * Compares the code provided by the user with expected values within a
 * given window.  Returns 1 if there was a match, 0 if not, and -1 if an
 * error occurred.  Also advances the counter if there was a match.
 */
int
oath_hotp_match(struct oath_key *k, unsigned int response, int window)
{
	unsigned int code;

	if (k == NULL)
		return (-1);
	if (window < 1)
		return (-1);
	if (k->mode != om_hotp)
		return (-1);
	if (k->counter >= UINT64_MAX - window)
		return (-1);
	for (int i = 0; i < window; ++i) {
		code = oath_hotp(k->key, k->keylen, k->counter + i, k->digits);
		if (code == response && !k->dummy) {
			k->counter = k->counter + i;
			return (1);
		}
	}
	return (0);
}