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/*

 * RTMP Diffie-Hellmann utilities

 * Copyright (c) 2009 Andrej Stepanchuk

 * Copyright (c) 2009-2010 Howard Chu

 * Copyright (c) 2012 Samuel Pitoiset

 *

 * This file is part of FFmpeg.

 *

 * FFmpeg is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public

 * License as published by the Free Software Foundation; either

 * version 2.1 of the License, or (at your option) any later version.

 *

 * FFmpeg is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public

 * License along with FFmpeg; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

/**

 * @file

 * RTMP Diffie-Hellmann utilities

 */

#include "config.h"

#include "rtmpdh.h"

#include "libavutil/random_seed.h"

#define P1024                                          \

    "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1" \

    "29024E088A67CC74020BBEA63B139B22514A08798E3404DD" \

    "EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245" \

    "E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED" \

    "EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381" \

    "FFFFFFFFFFFFFFFF"

#define Q1024                                          \

    "7FFFFFFFFFFFFFFFE487ED5110B4611A62633145C06E0E68" \

    "948127044533E63A0105DF531D89CD9128A5043CC71A026E" \

    "F7CA8CD9E69D218D98158536F92F8A1BA7F09AB6B6A8E122" \

    "F242DABB312F3F637A262174D31BF6B585FFAE5B7A035BF6" \

    "F71C35FDAD44CFD2D74F9208BE258FF324943328F67329C0" \

    "FFFFFFFFFFFFFFFF"

#if CONFIG_NETTLE || CONFIG_GCRYPT

#if CONFIG_NETTLE

#define bn_new(bn)                      \

    do {                                \

        bn = av_malloc(sizeof(*bn));    \

        if (bn)                         \

            mpz_init2(bn, 1);           \

    } while (0)

#define bn_free(bn)     \

    do {                \

        mpz_clear(bn);  \

        av_free(bn);    \

    } while (0)

#define bn_set_word(bn, w)          mpz_set_ui(bn, w)

#define bn_cmp(a, b)                mpz_cmp(a, b)

#define bn_copy(to, from)           mpz_set(to, from)

#define bn_sub_word(bn, w)          mpz_sub_ui(bn, bn, w)

#define bn_cmp_1(bn)                mpz_cmp_ui(bn, 1)

#define bn_num_bytes(bn)            (mpz_sizeinbase(bn, 2) + 7) / 8

#define bn_bn2bin(bn, buf, len)     nettle_mpz_get_str_256(len, buf, bn)

#define bn_bin2bn(bn, buf, len)                     \

    do {                                            \

        bn_new(bn);                                 \

        if (bn)                                     \

            nettle_mpz_set_str_256_u(bn, len, buf); \

    } while (0)

#define bn_hex2bn(bn, buf, ret)                     \

    do {                                            \

        bn_new(bn);                                 \

        if (bn)                                     \

            ret = (mpz_set_str(bn, buf, 16) == 0);  \

    } while (0)

#define bn_modexp(bn, y, q, p)      mpz_powm(bn, y, q, p)

#define bn_random(bn, num_bytes)                    \

    do {                                            \

        gmp_randstate_t rs;                         \

        gmp_randinit_mt(rs);                        \

        gmp_randseed_ui(rs, av_get_random_seed());  \

        mpz_urandomb(bn, rs, num_bytes);            \

        gmp_randclear(rs);                          \

    } while (0)

#elif CONFIG_GCRYPT

#define bn_new(bn)                  bn = gcry_mpi_new(1)

#define bn_free(bn)                 gcry_mpi_release(bn)

#define bn_set_word(bn, w)          gcry_mpi_set_ui(bn, w)

#define bn_cmp(a, b)                gcry_mpi_cmp(a, b)

#define bn_copy(to, from)           gcry_mpi_set(to, from)

#define bn_sub_word(bn, w)          gcry_mpi_sub_ui(bn, bn, w)

#define bn_cmp_1(bn)                gcry_mpi_cmp_ui(bn, 1)

#define bn_num_bytes(bn)            (gcry_mpi_get_nbits(bn) + 7) / 8

#define bn_bn2bin(bn, buf, len)     gcry_mpi_print(GCRYMPI_FMT_USG, buf, len, NULL, bn)

#define bn_bin2bn(bn, buf, len)     gcry_mpi_scan(&bn, GCRYMPI_FMT_USG, buf, len, NULL)

#define bn_hex2bn(bn, buf, ret)     ret = (gcry_mpi_scan(&bn, GCRYMPI_FMT_HEX, buf, 0, 0) == 0)

#define bn_modexp(bn, y, q, p)      gcry_mpi_powm(bn, y, q, p)

#define bn_random(bn, num_bytes)    gcry_mpi_randomize(bn, num_bytes, GCRY_WEAK_RANDOM)

#endif

#define MAX_BYTES 18000

#define dh_new()                    av_malloc(sizeof(FF_DH))

static FFBigNum dh_generate_key(FF_DH *dh)

{

    int num_bytes;

    num_bytes = bn_num_bytes(dh->p) - 1;

    if (num_bytes <= 0 || num_bytes > MAX_BYTES)

        return NULL;

    bn_new(dh->priv_key);

    if (!dh->priv_key)

        return NULL;

    bn_random(dh->priv_key, num_bytes);

    bn_new(dh->pub_key);

    if (!dh->pub_key) {

        bn_free(dh->priv_key);

        return NULL;

    }

    bn_modexp(dh->pub_key, dh->g, dh->priv_key, dh->p);

    return dh->pub_key;

}

static int dh_compute_key(FF_DH *dh, FFBigNum pub_key_bn,

                          uint32_t pub_key_len, uint8_t *secret_key)

{

    FFBigNum k;

    int num_bytes;

    num_bytes = bn_num_bytes(dh->p);

    if (num_bytes <= 0 || num_bytes > MAX_BYTES)

        return -1;

    bn_new(k);

    if (!k)

        return -1;

    bn_modexp(k, pub_key_bn, dh->priv_key, dh->p);

    bn_bn2bin(k, secret_key, pub_key_len);

    bn_free(k);

    /* return the length of the shared secret key like DH_compute_key */

    return pub_key_len;

}

void ff_dh_free(FF_DH *dh)

{

    bn_free(dh->p);

    bn_free(dh->g);

    bn_free(dh->pub_key);

    bn_free(dh->priv_key);

    av_free(dh);

}

#elif CONFIG_OPENSSL

#define bn_new(bn)                  bn = BN_new()

#define bn_free(bn)                 BN_free(bn)

#define bn_set_word(bn, w)          BN_set_word(bn, w)

#define bn_cmp(a, b)                BN_cmp(a, b)

#define bn_copy(to, from)           BN_copy(to, from)

#define bn_sub_word(bn, w)          BN_sub_word(bn, w)

#define bn_cmp_1(bn)                BN_cmp(bn, BN_value_one())

#define bn_num_bytes(bn)            BN_num_bytes(bn)

#define bn_bn2bin(bn, buf, len)     BN_bn2bin(bn, buf)

#define bn_bin2bn(bn, buf, len)     bn = BN_bin2bn(buf, len, 0)

#define bn_hex2bn(bn, buf, ret)     ret = BN_hex2bn(&bn, buf)

#define bn_modexp(bn, y, q, p)               \

    do {                                     \

        BN_CTX *ctx = BN_CTX_new();          \

        if (!ctx)                            \

            return AVERROR(ENOMEM);          \

        if (!BN_mod_exp(bn, y, q, p, ctx)) { \

            BN_CTX_free(ctx);                \

            return AVERROR(EINVAL);          \

        }                                    \

        BN_CTX_free(ctx);                    \

    } while (0)

#define dh_new()                                DH_new()

#define dh_generate_key(dh)                     DH_generate_key(dh)

#define dh_compute_key(dh, pub, len, secret)    DH_compute_key(secret, pub, dh)

void ff_dh_free(FF_DH *dh)

{

    DH_free(dh);

}

#endif

static int dh_is_valid_public_key(FFBigNum y, FFBigNum p, FFBigNum q)

{

    FFBigNum bn = NULL;

    int ret = AVERROR(EINVAL);

    bn_new(bn);

    if (!bn)

        return AVERROR(ENOMEM);

    /* y must lie in [2, p - 1] */

    bn_set_word(bn, 1);

    if (!bn_cmp(y, bn))

        goto fail;

    /* bn = p - 2 */

    bn_copy(bn, p);

    bn_sub_word(bn, 1);

    if (!bn_cmp(y, bn))

        goto fail;

    /* Verify with Sophie-Germain prime

     *

     * This is a nice test to make sure the public key position is calculated

     * correctly. This test will fail in about 50% of the cases if applied to

     * random data.

     */

    /* y must fulfill y^q mod p = 1 */

    bn_modexp(bn, y, q, p);

    if (bn_cmp_1(bn))

        goto fail;

    ret = 0;

fail:

    bn_free(bn);

    return ret;

}

av_cold FF_DH *ff_dh_init(int key_len)

{

    FF_DH *dh;

    int ret;

    if (!(dh = dh_new()))

        return NULL;

    bn_new(dh->g);

    if (!dh->g)

        goto fail;

    bn_hex2bn(dh->p, P1024, ret);

    if (!ret)

        goto fail;

    bn_set_word(dh->g, 2);

    dh->length = key_len;

    return dh;

fail:

    ff_dh_free(dh);

    return NULL;

}

int ff_dh_generate_public_key(FF_DH *dh)

{

    int ret = 0;

    while (!ret) {

        FFBigNum q1 = NULL;

        if (!dh_generate_key(dh))

            return AVERROR(EINVAL);

        bn_hex2bn(q1, Q1024, ret);

        if (!ret)

            return AVERROR(ENOMEM);

        ret = dh_is_valid_public_key(dh->pub_key, dh->p, q1);

        bn_free(q1);

        if (!ret) {

            /* the public key is valid */

            break;

        }

    }

    return ret;

}

int ff_dh_write_public_key(FF_DH *dh, uint8_t *pub_key, int pub_key_len)

{

    int len;

    /* compute the length of the public key */

    len = bn_num_bytes(dh->pub_key);

    if (len <= 0 || len > pub_key_len)

        return AVERROR(EINVAL);

    /* convert the public key value into big-endian form */

    memset(pub_key, 0, pub_key_len);

    bn_bn2bin(dh->pub_key, pub_key + pub_key_len - len, len);

    return 0;

}

int ff_dh_compute_shared_secret_key(FF_DH *dh, const uint8_t *pub_key,

                                    int pub_key_len, uint8_t *secret_key)

{

    FFBigNum q1 = NULL, pub_key_bn = NULL;

    int ret;

    /* convert the big-endian form of the public key into a bignum */

    bn_bin2bn(pub_key_bn, pub_key, pub_key_len);

    if (!pub_key_bn)

        return AVERROR(ENOMEM);

    /* convert the string containing a hexadecimal number into a bignum */

    bn_hex2bn(q1, Q1024, ret);

    if (!ret) {

        ret = AVERROR(ENOMEM);

        goto fail;

    }

    /* when the public key is valid we have to compute the shared secret key */

    if ((ret = dh_is_valid_public_key(pub_key_bn, dh->p, q1)) < 0) {

        goto fail;

    } else if ((ret = dh_compute_key(dh, pub_key_bn, pub_key_len,

                                     secret_key)) < 0) {

        ret = AVERROR(EINVAL);

        goto fail;

    }

fail:

    bn_free(pub_key_bn);

    bn_free(q1);

    return ret;

}