libavformat/rtmpdh.c

   1 /*
   2  * RTMP Diffie-Hellmann utilities
   3  * Copyright (c) 2009 Andrej Stepanchuk
   4  * Copyright (c) 2009-2010 Howard Chu
   5  * Copyright (c) 2012 Samuel Pitoiset
   6  *
   7  * This file is part of FFmpeg.
   8  *
   9  * FFmpeg is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public
  11  * License as published by the Free Software Foundation; either
  12  * version 2.1 of the License, or (at your option) any later version.
  13  *
  14  * FFmpeg is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with FFmpeg; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22  */
  23
  24 /**
  25  * @file
  26  * RTMP Diffie-Hellmann utilities
  27  */
  28
  29 #include <stdint.h>
  30 #include <string.h>
  31
  32 #include "config.h"
  33
  34 #include "libavutil/attributes.h"
  35 #include "libavutil/error.h"
  36 #include "libavutil/mem.h"
  37 #include "libavutil/random_seed.h"
  38
  39 #include "rtmpdh.h"
  40
  41 #if CONFIG_MBEDTLS
  42 #include <mbedtls/ctr_drbg.h>
  43 #include <mbedtls/entropy.h>
  44 #endif
  45
  46 #define P1024                                          \
  47     "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1" \
  48     "29024E088A67CC74020BBEA63B139B22514A08798E3404DD" \
  49     "EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245" \
  50     "E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED" \
  51     "EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381" \
  52     "FFFFFFFFFFFFFFFF"
  53
  54 #define Q1024                                          \
  55     "7FFFFFFFFFFFFFFFE487ED5110B4611A62633145C06E0E68" \
  56     "948127044533E63A0105DF531D89CD9128A5043CC71A026E" \
  57     "F7CA8CD9E69D218D98158536F92F8A1BA7F09AB6B6A8E122" \
  58     "F242DABB312F3F637A262174D31BF6B585FFAE5B7A035BF6" \
  59     "F71C35FDAD44CFD2D74F9208BE258FF324943328F67329C0" \
  60     "FFFFFFFFFFFFFFFF"
  61
  62 #if CONFIG_GMP
  63 #define bn_new(bn)                      \
  64     do {                                \
  65         bn = av_malloc(sizeof(*bn));    \
  66         if (bn)                         \
  67             mpz_init2(bn, 1);           \
  68     } while (0)
  69 #define bn_free(bn)     \
  70     do {                \
  71         mpz_clear(bn);  \
  72         av_free(bn);    \
  73     } while (0)
  74 #define bn_set_word(bn, w)          mpz_set_ui(bn, w)
  75 #define bn_cmp(a, b)                mpz_cmp(a, b)
  76 #define bn_copy(to, from)           mpz_set(to, from)
  77 #define bn_sub_word(bn, w)          mpz_sub_ui(bn, bn, w)
  78 #define bn_cmp_1(bn)                mpz_cmp_ui(bn, 1)
  79 #define bn_num_bytes(bn)            (mpz_sizeinbase(bn, 2) + 7) / 8
  80 #define bn_bn2bin(bn, buf, len)                     \
  81     do {                                            \
  82         memset(buf, 0, len);                        \
  83         if (bn_num_bytes(bn) <= len)                \
  84             mpz_export(buf, NULL, 1, 1, 0, 0, bn);  \
  85     } while (0)
  86 #define bn_bin2bn(bn, buf, len)                     \
  87     do {                                            \
  88         bn_new(bn);                                 \
  89         if (bn)                                     \
  90             mpz_import(bn, len, 1, 1, 0, 0, buf);   \
  91     } while (0)
  92 #define bn_hex2bn(bn, buf, ret)                     \
  93     do {                                            \
  94         bn_new(bn);                                 \
  95         if (bn)                                     \
  96             ret = (mpz_set_str(bn, buf, 16) == 0);  \
  97         else                                        \
  98             ret = 1;                                \
  99     } while (0)
 100 #define bn_random(bn, num_bits)                       \
 101     do {                                              \
 102         int bits = num_bits;                          \
 103         mpz_set_ui(bn, 0);                            \
 104         for (bits = num_bits; bits > 0; bits -= 32) { \
 105             mpz_mul_2exp(bn, bn, 32);                 \
 106             mpz_add_ui(bn, bn, av_get_random_seed()); \
 107         }                                             \
 108         mpz_fdiv_r_2exp(bn, bn, num_bits);            \
 109     } while (0)
 110 static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
 111 {
 112     mpz_powm(bn, y, q, p);
 113     return 0;
 114 }
 115 #elif CONFIG_GCRYPT
 116 #define bn_new(bn)                                                \
 117     do {                                                          \
 118         if (!gcry_control(GCRYCTL_INITIALIZATION_FINISHED_P)) {   \
 119             if (gcry_check_version("1.5.4")) {                    \
 120                 gcry_control(GCRYCTL_DISABLE_SECMEM, 0);          \
 121                 gcry_control(GCRYCTL_INITIALIZATION_FINISHED, 0); \
 122             }                                                     \
 123         }                                                         \
 124         if (gcry_control(GCRYCTL_INITIALIZATION_FINISHED_P))      \
 125             bn = gcry_mpi_new(1);                                 \
 126         else                                                      \
 127             bn = NULL;                                            \
 128     } while (0)
 129 #define bn_free(bn)                 gcry_mpi_release(bn)
 130 #define bn_set_word(bn, w)          gcry_mpi_set_ui(bn, w)
 131 #define bn_cmp(a, b)                gcry_mpi_cmp(a, b)
 132 #define bn_copy(to, from)           gcry_mpi_set(to, from)
 133 #define bn_sub_word(bn, w)          gcry_mpi_sub_ui(bn, bn, w)
 134 #define bn_cmp_1(bn)                gcry_mpi_cmp_ui(bn, 1)
 135 #define bn_num_bytes(bn)            (gcry_mpi_get_nbits(bn) + 7) / 8
 136 #define bn_bn2bin(bn, buf, len)     gcry_mpi_print(GCRYMPI_FMT_USG, buf, len, NULL, bn)
 137 #define bn_bin2bn(bn, buf, len)     gcry_mpi_scan(&bn, GCRYMPI_FMT_USG, buf, len, NULL)
 138 #define bn_hex2bn(bn, buf, ret)     ret = (gcry_mpi_scan(&bn, GCRYMPI_FMT_HEX, buf, 0, 0) == 0)
 139 #define bn_random(bn, num_bits)     gcry_mpi_randomize(bn, num_bits, GCRY_WEAK_RANDOM)
 140 static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
 141 {
 142     gcry_mpi_powm(bn, y, q, p);
 143     return 0;
 144 }
 145 #elif CONFIG_OPENSSL
 146 #define bn_new(bn)                  bn = BN_new()
 147 #define bn_free(bn)                 BN_free(bn)
 148 #define bn_set_word(bn, w)          BN_set_word(bn, w)
 149 #define bn_cmp(a, b)                BN_cmp(a, b)
 150 #define bn_copy(to, from)           BN_copy(to, from)
 151 #define bn_sub_word(bn, w)          BN_sub_word(bn, w)
 152 #define bn_cmp_1(bn)                BN_cmp(bn, BN_value_one())
 153 #define bn_num_bytes(bn)            BN_num_bytes(bn)
 154 #define bn_bn2bin(bn, buf, len)     BN_bn2bin(bn, buf)
 155 #define bn_bin2bn(bn, buf, len)     bn = BN_bin2bn(buf, len, 0)
 156 #define bn_hex2bn(bn, buf, ret)     ret = BN_hex2bn(&bn, buf)
 157 #define bn_random(bn, num_bits)     BN_rand(bn, num_bits, 0, 0)
 158 static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
 159 {
 160     BN_CTX *ctx = BN_CTX_new();
 161     if (!ctx)
 162         return AVERROR(ENOMEM);
 163     if (!BN_mod_exp(bn, y, q, p, ctx)) {
 164         BN_CTX_free(ctx);
 165         return AVERROR(EINVAL);
 166     }
 167     BN_CTX_free(ctx);
 168     return 0;
 169 }
 170 #elif CONFIG_MBEDTLS
 171 #define bn_new(bn)                      \
 172     do {                                \
 173         bn = av_malloc(sizeof(*bn));    \
 174         if (bn)                         \
 175             mbedtls_mpi_init(bn);       \
 176     } while (0)
 177 #define bn_free(bn)                     \
 178     do {                                \
 179         mbedtls_mpi_free(bn);           \
 180         av_free(bn);                    \
 181     } while (0)
 182 #define bn_set_word(bn, w)          mbedtls_mpi_lset(bn, w)
 183 #define bn_cmp(a, b)                mbedtls_mpi_cmp_mpi(a, b)
 184 #define bn_copy(to, from)           mbedtls_mpi_copy(to, from)
 185 #define bn_sub_word(bn, w)          mbedtls_mpi_sub_int(bn, bn, w)
 186 #define bn_cmp_1(bn)                mbedtls_mpi_cmp_int(bn, 1)
 187 #define bn_num_bytes(bn)            (mbedtls_mpi_bitlen(bn) + 7) / 8
 188 #define bn_bn2bin(bn, buf, len)     mbedtls_mpi_write_binary(bn, buf, len)
 189 #define bn_bin2bn(bn, buf, len)                     \
 190     do {                                            \
 191         bn_new(bn);                                 \
 192         if (bn)                                     \
 193             mbedtls_mpi_read_binary(bn, buf, len);  \
 194     } while (0)
 195 #define bn_hex2bn(bn, buf, ret)                     \
 196     do {                                            \
 197         bn_new(bn);                                 \
 198         if (bn)                                     \
 199             ret = (mbedtls_mpi_read_string(bn, 16, buf) == 0);  \
 200         else                                        \
 201             ret = 1;                                \
 202     } while (0)
 203 #define bn_random(bn, num_bits)                     \
 204     do {                                            \
 205         mbedtls_entropy_context entropy_ctx;        \
 206         mbedtls_ctr_drbg_context ctr_drbg_ctx;      \
 207                                                     \
 208         mbedtls_entropy_init(&entropy_ctx);         \
 209         mbedtls_ctr_drbg_init(&ctr_drbg_ctx);       \
 210         mbedtls_ctr_drbg_seed(&ctr_drbg_ctx,        \
 211                               mbedtls_entropy_func, \
 212                               &entropy_ctx,         \
 213                               NULL, 0);             \
 214         mbedtls_mpi_fill_random(bn, (num_bits + 7) / 8, mbedtls_ctr_drbg_random, &ctr_drbg_ctx); \
 215         mbedtls_ctr_drbg_free(&ctr_drbg_ctx);       \
 216         mbedtls_entropy_free(&entropy_ctx);         \
 217     } while (0)
 218 #define bn_modexp(bn, y, q, p)      mbedtls_mpi_exp_mod(bn, y, q, p, 0)
 219
 220 #endif
 221
 222 #define MAX_BYTES 18000
 223
 224 #define dh_new()                    av_mallocz(sizeof(FF_DH))
 225
 226 static FFBigNum dh_generate_key(FF_DH *dh)
 227 {
 228     int num_bytes;
 229
 230     num_bytes = bn_num_bytes(dh->p) - 1;
 231     if (num_bytes <= 0 || num_bytes > MAX_BYTES)
 232         return NULL;
 233
 234     bn_new(dh->priv_key);
 235     if (!dh->priv_key)
 236         return NULL;
 237     bn_random(dh->priv_key, 8 * num_bytes);
 238
 239     bn_new(dh->pub_key);
 240     if (!dh->pub_key) {
 241         bn_free(dh->priv_key);
 242         return NULL;
 243     }
 244
 245     if (bn_modexp(dh->pub_key, dh->g, dh->priv_key, dh->p) < 0)
 246         return NULL;
 247
 248     return dh->pub_key;
 249 }
 250
 251 static int dh_compute_key(FF_DH *dh, FFBigNum pub_key_bn,
 252                           uint32_t secret_key_len, uint8_t *secret_key)
 253 {
 254     FFBigNum k;
 255     int ret;
 256
 257     bn_new(k);
 258     if (!k)
 259         return -1;
 260
 261     if ((ret = bn_modexp(k, pub_key_bn, dh->priv_key, dh->p)) < 0) {
 262         bn_free(k);
 263         return ret;
 264     }
 265     bn_bn2bin(k, secret_key, secret_key_len);
 266     bn_free(k);
 267
 268     /* return the length of the shared secret key like DH_compute_key */
 269     return secret_key_len;
 270 }
 271
 272 void ff_dh_free(FF_DH *dh)
 273 {
 274     if (!dh)
 275         return;
 276     bn_free(dh->p);
 277     bn_free(dh->g);
 278     bn_free(dh->pub_key);
 279     bn_free(dh->priv_key);
 280     av_free(dh);
 281 }
 282
 283 static int dh_is_valid_public_key(FFBigNum y, FFBigNum p, FFBigNum q)
 284 {
 285     FFBigNum bn = NULL;
 286     int ret = AVERROR(EINVAL);
 287
 288     bn_new(bn);
 289     if (!bn)
 290         return AVERROR(ENOMEM);
 291
 292     /* y must lie in [2, p - 1] */
 293     bn_set_word(bn, 1);
 294     if (!bn_cmp(y, bn))
 295         goto fail;
 296
 297     /* bn = p - 2 */
 298     bn_copy(bn, p);
 299     bn_sub_word(bn, 1);
 300     if (!bn_cmp(y, bn))
 301         goto fail;
 302
 303     /* Verify with Sophie-Germain prime
 304      *
 305      * This is a nice test to make sure the public key position is calculated
 306      * correctly. This test will fail in about 50% of the cases if applied to
 307      * random data.
 308      */
 309     /* y must fulfill y^q mod p = 1 */
 310     if ((ret = bn_modexp(bn, y, q, p)) < 0)
 311         goto fail;
 312
 313     ret = AVERROR(EINVAL);
 314     if (bn_cmp_1(bn))
 315         goto fail;
 316
 317     ret = 0;
 318 fail:
 319     bn_free(bn);
 320
 321     return ret;
 322 }
 323
 324 av_cold FF_DH *ff_dh_init(int key_len)
 325 {
 326     FF_DH *dh;
 327     int ret;
 328
 329     if (!(dh = dh_new()))
 330         return NULL;
 331
 332     bn_new(dh->g);
 333     if (!dh->g)
 334         goto fail;
 335
 336     bn_hex2bn(dh->p, P1024, ret);
 337     if (!ret)
 338         goto fail;
 339
 340     bn_set_word(dh->g, 2);
 341     dh->length = key_len;
 342
 343     return dh;
 344
 345 fail:
 346     ff_dh_free(dh);
 347
 348     return NULL;
 349 }
 350
 351 int ff_dh_generate_public_key(FF_DH *dh)
 352 {
 353     int ret = 0;
 354
 355     while (!ret) {
 356         FFBigNum q1 = NULL;
 357
 358         if (!dh_generate_key(dh))
 359             return AVERROR(EINVAL);
 360
 361         bn_hex2bn(q1, Q1024, ret);
 362         if (!ret)
 363             return AVERROR(ENOMEM);
 364
 365         ret = dh_is_valid_public_key(dh->pub_key, dh->p, q1);
 366         bn_free(q1);
 367
 368         if (!ret) {
 369             /* the public key is valid */
 370             break;
 371         }
 372     }
 373
 374     return ret;
 375 }
 376
 377 int ff_dh_write_public_key(FF_DH *dh, uint8_t *pub_key, int pub_key_len)
 378 {
 379     int len;
 380
 381     /* compute the length of the public key */
 382     len = bn_num_bytes(dh->pub_key);
 383     if (len <= 0 || len > pub_key_len)
 384         return AVERROR(EINVAL);
 385
 386     /* convert the public key value into big-endian form */
 387     memset(pub_key, 0, pub_key_len);
 388     bn_bn2bin(dh->pub_key, pub_key + pub_key_len - len, len);
 389
 390     return 0;
 391 }
 392
 393 int ff_dh_compute_shared_secret_key(FF_DH *dh, const uint8_t *pub_key,
 394                                     int pub_key_len, uint8_t *secret_key,
 395                                     int secret_key_len)
 396 {
 397     FFBigNum q1 = NULL, pub_key_bn = NULL;
 398     int ret;
 399
 400     /* convert the big-endian form of the public key into a bignum */
 401     bn_bin2bn(pub_key_bn, pub_key, pub_key_len);
 402     if (!pub_key_bn)
 403         return AVERROR(ENOMEM);
 404
 405     /* convert the string containing a hexadecimal number into a bignum */
 406     bn_hex2bn(q1, Q1024, ret);
 407     if (!ret) {
 408         ret = AVERROR(ENOMEM);
 409         goto fail;
 410     }
 411
 412     /* when the public key is valid we have to compute the shared secret key */
 413     if ((ret = dh_is_valid_public_key(pub_key_bn, dh->p, q1)) < 0) {
 414         goto fail;
 415     } else if ((ret = dh_compute_key(dh, pub_key_bn, secret_key_len,
 416                                      secret_key)) < 0) {
 417         ret = AVERROR(EINVAL);
 418         goto fail;
 419     }
 420
 421 fail:
 422     bn_free(pub_key_bn);
 423     bn_free(q1);
 424
 425     return ret;
 426 }