source: openpam/trunk/lib/liboath/oath_hotp.c @ 679

/*-
 * 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.
 *
 * $Id: oath_hotp.c 679 2013-03-18 21:38:58Z des $
 */

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <openssl/evp.h>
#include <openssl/hmac.h>

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

#include <security/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];
        unsigned int HSlen;
        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_CTX_init(&ctx);
        HMAC_Init_ex(&ctx, K, Klen, EVP_sha1(), NULL);
        HMAC_Update(&ctx, (const uint8_t *)&C, sizeof C);
        HMAC_Final(&ctx, HS, &HSlen);
        HMAC_CTX_cleanup(&ctx);

        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.
 */
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.
 */
int
oath_hotp_match(struct oath_key *k, unsigned int response, int window)
{
        unsigned int code;
        int dummy;

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