FFmpeg: libavformat/rtmpdh.c Source File

00001 /*
00002  * RTMP Diffie-Hellmann utilities
00003  * Copyright (c) 2009 Andrej Stepanchuk
00004  * Copyright (c) 2009-2010 Howard Chu
00005  * Copyright (c) 2012 Samuel Pitoiset
00006  *
00007  * This file is part of FFmpeg.
00008  *
00009  * FFmpeg is free software; you can redistribute it and/or
00010  * modify it under the terms of the GNU Lesser General Public
00011  * License as published by the Free Software Foundation; either
00012  * version 2.1 of the License, or (at your option) any later version.
00013  *
00014  * FFmpeg is distributed in the hope that it will be useful,
00015  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00016  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00017  * Lesser General Public License for more details.
00018  *
00019  * You should have received a copy of the GNU Lesser General Public
00020  * License along with FFmpeg; if not, write to the Free Software
00021  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00022  */
00023 
00029 #include "config.h"
00030 #include "rtmpdh.h"
00031 #include "libavutil/random_seed.h"
00032 
00033 #define P1024                                          \
00034     "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1" \
00035     "29024E088A67CC74020BBEA63B139B22514A08798E3404DD" \
00036     "EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245" \
00037     "E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED" \
00038     "EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381" \
00039     "FFFFFFFFFFFFFFFF"
00040 
00041 #define Q1024                                          \
00042     "7FFFFFFFFFFFFFFFE487ED5110B4611A62633145C06E0E68" \
00043     "948127044533E63A0105DF531D89CD9128A5043CC71A026E" \
00044     "F7CA8CD9E69D218D98158536F92F8A1BA7F09AB6B6A8E122" \
00045     "F242DABB312F3F637A262174D31BF6B585FFAE5B7A035BF6" \
00046     "F71C35FDAD44CFD2D74F9208BE258FF324943328F67329C0" \
00047     "FFFFFFFFFFFFFFFF"
00048 
00049 #if CONFIG_NETTLE || CONFIG_GCRYPT
00050 #if CONFIG_NETTLE
00051 #define bn_new(bn)                      \
00052     do {                                \
00053         bn = av_malloc(sizeof(*bn));    \
00054         if (bn)                         \
00055             mpz_init2(bn, 1);           \
00056     } while (0)
00057 #define bn_free(bn)     \
00058     do {                \
00059         mpz_clear(bn);  \
00060         av_free(bn);    \
00061     } while (0)
00062 #define bn_set_word(bn, w)          mpz_set_ui(bn, w)
00063 #define bn_cmp(a, b)                mpz_cmp(a, b)
00064 #define bn_copy(to, from)           mpz_set(to, from)
00065 #define bn_sub_word(bn, w)          mpz_sub_ui(bn, bn, w)
00066 #define bn_cmp_1(bn)                mpz_cmp_ui(bn, 1)
00067 #define bn_num_bytes(bn)            (mpz_sizeinbase(bn, 2) + 7) / 8
00068 #define bn_bn2bin(bn, buf, len)     nettle_mpz_get_str_256(len, buf, bn)
00069 #define bn_bin2bn(bn, buf, len)                     \
00070     do {                                            \
00071         bn_new(bn);                                 \
00072         if (bn)                                     \
00073             nettle_mpz_set_str_256_u(bn, len, buf); \
00074     } while (0)
00075 #define bn_hex2bn(bn, buf, ret)                     \
00076     do {                                            \
00077         bn_new(bn);                                 \
00078         if (bn)                                     \
00079             ret = (mpz_set_str(bn, buf, 16) == 0);  \
00080     } while (0)
00081 #define bn_modexp(bn, y, q, p)      mpz_powm(bn, y, q, p)
00082 #define bn_random(bn, num_bytes)                    \
00083     do {                                            \
00084         gmp_randstate_t rs;                         \
00085         gmp_randinit_mt(rs);                        \
00086         gmp_randseed_ui(rs, av_get_random_seed());  \
00087         mpz_urandomb(bn, rs, num_bytes);            \
00088         gmp_randclear(rs);                          \
00089     } while (0)
00090 #elif CONFIG_GCRYPT
00091 #define bn_new(bn)                  bn = gcry_mpi_new(1)
00092 #define bn_free(bn)                 gcry_mpi_release(bn)
00093 #define bn_set_word(bn, w)          gcry_mpi_set_ui(bn, w)
00094 #define bn_cmp(a, b)                gcry_mpi_cmp(a, b)
00095 #define bn_copy(to, from)           gcry_mpi_set(to, from)
00096 #define bn_sub_word(bn, w)          gcry_mpi_sub_ui(bn, bn, w)
00097 #define bn_cmp_1(bn)                gcry_mpi_cmp_ui(bn, 1)
00098 #define bn_num_bytes(bn)            (gcry_mpi_get_nbits(bn) + 7) / 8
00099 #define bn_bn2bin(bn, buf, len)     gcry_mpi_print(GCRYMPI_FMT_USG, buf, len, NULL, bn)
00100 #define bn_bin2bn(bn, buf, len)     gcry_mpi_scan(&bn, GCRYMPI_FMT_USG, buf, len, NULL)
00101 #define bn_hex2bn(bn, buf, ret)     ret = (gcry_mpi_scan(&bn, GCRYMPI_FMT_HEX, buf, 0, 0) == 0)
00102 #define bn_modexp(bn, y, q, p)      gcry_mpi_powm(bn, y, q, p)
00103 #define bn_random(bn, num_bytes)    gcry_mpi_randomize(bn, num_bytes, GCRY_WEAK_RANDOM)
00104 #endif
00105 
00106 #define MAX_BYTES 18000
00107 
00108 #define dh_new()                    av_malloc(sizeof(FF_DH))
00109 
00110 static FFBigNum dh_generate_key(FF_DH *dh)
00111 {
00112     int num_bytes;
00113 
00114     num_bytes = bn_num_bytes(dh->p) - 1;
00115     if (num_bytes <= 0 || num_bytes > MAX_BYTES)
00116         return NULL;
00117 
00118     bn_new(dh->priv_key);
00119     if (!dh->priv_key)
00120         return NULL;
00121     bn_random(dh->priv_key, num_bytes);
00122 
00123     bn_new(dh->pub_key);
00124     if (!dh->pub_key) {
00125         bn_free(dh->priv_key);
00126         return NULL;
00127     }
00128 
00129     bn_modexp(dh->pub_key, dh->g, dh->priv_key, dh->p);
00130 
00131     return dh->pub_key;
00132 }
00133 
00134 static int dh_compute_key(FF_DH *dh, FFBigNum pub_key_bn,
00135                           uint32_t pub_key_len, uint8_t *secret_key)
00136 {
00137     FFBigNum k;
00138     int num_bytes;
00139 
00140     num_bytes = bn_num_bytes(dh->p);
00141     if (num_bytes <= 0 || num_bytes > MAX_BYTES)
00142         return -1;
00143 
00144     bn_new(k);
00145     if (!k)
00146         return -1;
00147 
00148     bn_modexp(k, pub_key_bn, dh->priv_key, dh->p);
00149     bn_bn2bin(k, secret_key, pub_key_len);
00150     bn_free(k);
00151 
00152     /* return the length of the shared secret key like DH_compute_key */
00153     return pub_key_len;
00154 }
00155 
00156 void ff_dh_free(FF_DH *dh)
00157 {
00158     bn_free(dh->p);
00159     bn_free(dh->g);
00160     bn_free(dh->pub_key);
00161     bn_free(dh->priv_key);
00162     av_free(dh);
00163 }
00164 #elif CONFIG_OPENSSL
00165 #define bn_new(bn)                  bn = BN_new()
00166 #define bn_free(bn)                 BN_free(bn)
00167 #define bn_set_word(bn, w)          BN_set_word(bn, w)
00168 #define bn_cmp(a, b)                BN_cmp(a, b)
00169 #define bn_copy(to, from)           BN_copy(to, from)
00170 #define bn_sub_word(bn, w)          BN_sub_word(bn, w)
00171 #define bn_cmp_1(bn)                BN_cmp(bn, BN_value_one())
00172 #define bn_num_bytes(bn)            BN_num_bytes(bn)
00173 #define bn_bn2bin(bn, buf, len)     BN_bn2bin(bn, buf)
00174 #define bn_bin2bn(bn, buf, len)     bn = BN_bin2bn(buf, len, 0)
00175 #define bn_hex2bn(bn, buf, ret)     ret = BN_hex2bn(&bn, buf)
00176 #define bn_modexp(bn, y, q, p)               \
00177     do {                                     \
00178         BN_CTX *ctx = BN_CTX_new();          \
00179         if (!ctx)                            \
00180             return AVERROR(ENOMEM);          \
00181         if (!BN_mod_exp(bn, y, q, p, ctx)) { \
00182             BN_CTX_free(ctx);                \
00183             return AVERROR(EINVAL);          \
00184         }                                    \
00185         BN_CTX_free(ctx);                    \
00186     } while (0)
00187 
00188 #define dh_new()                                DH_new()
00189 #define dh_generate_key(dh)                     DH_generate_key(dh)
00190 #define dh_compute_key(dh, pub, len, secret)    DH_compute_key(secret, pub, dh)
00191 
00192 void ff_dh_free(FF_DH *dh)
00193 {
00194     DH_free(dh);
00195 }
00196 #endif
00197 
00198 static int dh_is_valid_public_key(FFBigNum y, FFBigNum p, FFBigNum q)
00199 {
00200     FFBigNum bn = NULL;
00201     int ret = AVERROR(EINVAL);
00202 
00203     bn_new(bn);
00204     if (!bn)
00205         return AVERROR(ENOMEM);
00206 
00207     /* y must lie in [2, p - 1] */
00208     bn_set_word(bn, 1);
00209     if (!bn_cmp(y, bn))
00210         goto fail;
00211 
00212     /* bn = p - 2 */
00213     bn_copy(bn, p);
00214     bn_sub_word(bn, 1);
00215     if (!bn_cmp(y, bn))
00216         goto fail;
00217 
00218     /* Verify with Sophie-Germain prime
00219      *
00220      * This is a nice test to make sure the public key position is calculated
00221      * correctly. This test will fail in about 50% of the cases if applied to
00222      * random data.
00223      */
00224     /* y must fulfill y^q mod p = 1 */
00225     bn_modexp(bn, y, q, p);
00226 
00227     if (bn_cmp_1(bn))
00228         goto fail;
00229 
00230     ret = 0;
00231 fail:
00232     bn_free(bn);
00233 
00234     return ret;
00235 }
00236 
00237 av_cold FF_DH *ff_dh_init(int key_len)
00238 {
00239     FF_DH *dh;
00240     int ret;
00241 
00242     if (!(dh = dh_new()))
00243         return NULL;
00244 
00245     bn_new(dh->g);
00246     if (!dh->g)
00247         goto fail;
00248 
00249     bn_hex2bn(dh->p, P1024, ret);
00250     if (!ret)
00251         goto fail;
00252 
00253     bn_set_word(dh->g, 2);
00254     dh->length = key_len;
00255 
00256     return dh;
00257 
00258 fail:
00259     ff_dh_free(dh);
00260 
00261     return NULL;
00262 }
00263 
00264 int ff_dh_generate_public_key(FF_DH *dh)
00265 {
00266     int ret = 0;
00267 
00268     while (!ret) {
00269         FFBigNum q1 = NULL;
00270 
00271         if (!dh_generate_key(dh))
00272             return AVERROR(EINVAL);
00273 
00274         bn_hex2bn(q1, Q1024, ret);
00275         if (!ret)
00276             return AVERROR(ENOMEM);
00277 
00278         ret = dh_is_valid_public_key(dh->pub_key, dh->p, q1);
00279         bn_free(q1);
00280 
00281         if (!ret) {
00282             /* the public key is valid */
00283             break;
00284         }
00285     }
00286 
00287     return ret;
00288 }
00289 
00290 int ff_dh_write_public_key(FF_DH *dh, uint8_t *pub_key, int pub_key_len)
00291 {
00292     int len;
00293 
00294     /* compute the length of the public key */
00295     len = bn_num_bytes(dh->pub_key);
00296     if (len <= 0 || len > pub_key_len)
00297         return AVERROR(EINVAL);
00298 
00299     /* convert the public key value into big-endian form */
00300     memset(pub_key, 0, pub_key_len);
00301     bn_bn2bin(dh->pub_key, pub_key + pub_key_len - len, len);
00302 
00303     return 0;
00304 }
00305 
00306 int ff_dh_compute_shared_secret_key(FF_DH *dh, const uint8_t *pub_key,
00307                                     int pub_key_len, uint8_t *secret_key)
00308 {
00309     FFBigNum q1 = NULL, pub_key_bn = NULL;
00310     int ret;
00311 
00312     /* convert the big-endian form of the public key into a bignum */
00313     bn_bin2bn(pub_key_bn, pub_key, pub_key_len);
00314     if (!pub_key_bn)
00315         return AVERROR(ENOMEM);
00316 
00317     /* convert the string containing a hexadecimal number into a bignum */
00318     bn_hex2bn(q1, Q1024, ret);
00319     if (!ret) {
00320         ret = AVERROR(ENOMEM);
00321         goto fail;
00322     }
00323 
00324     /* when the public key is valid we have to compute the shared secret key */
00325     if ((ret = dh_is_valid_public_key(pub_key_bn, dh->p, q1)) < 0) {
00326         goto fail;
00327     } else if ((ret = dh_compute_key(dh, pub_key_bn, pub_key_len,
00328                                      secret_key)) < 0) {
00329         ret = AVERROR(EINVAL);
00330         goto fail;
00331     }
00332 
00333 fail:
00334     bn_free(pub_key_bn);
00335     bn_free(q1);
00336 
00337     return ret;
00338 }
00339