/*
  * 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;
 }