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rtmpdh.c
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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 "config.h"
30 #include "rtmpdh.h"
31 #include "libavutil/random_seed.h"
32 
33 #define P1024 \
34  "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1" \
35  "29024E088A67CC74020BBEA63B139B22514A08798E3404DD" \
36  "EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245" \
37  "E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED" \
38  "EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381" \
39  "FFFFFFFFFFFFFFFF"
40 
41 #define Q1024 \
42  "7FFFFFFFFFFFFFFFE487ED5110B4611A62633145C06E0E68" \
43  "948127044533E63A0105DF531D89CD9128A5043CC71A026E" \
44  "F7CA8CD9E69D218D98158536F92F8A1BA7F09AB6B6A8E122" \
45  "F242DABB312F3F637A262174D31BF6B585FFAE5B7A035BF6" \
46  "F71C35FDAD44CFD2D74F9208BE258FF324943328F67329C0" \
47  "FFFFFFFFFFFFFFFF"
48 
49 #if CONFIG_NETTLE || CONFIG_GCRYPT
50 #if CONFIG_NETTLE
51 #define bn_new(bn) \
52  do { \
53  bn = av_malloc(sizeof(*bn)); \
54  if (bn) \
55  mpz_init2(bn, 1); \
56  } while (0)
57 #define bn_free(bn) \
58  do { \
59  mpz_clear(bn); \
60  av_free(bn); \
61  } while (0)
62 #define bn_set_word(bn, w) mpz_set_ui(bn, w)
63 #define bn_cmp(a, b) mpz_cmp(a, b)
64 #define bn_copy(to, from) mpz_set(to, from)
65 #define bn_sub_word(bn, w) mpz_sub_ui(bn, bn, w)
66 #define bn_cmp_1(bn) mpz_cmp_ui(bn, 1)
67 #define bn_num_bytes(bn) (mpz_sizeinbase(bn, 2) + 7) / 8
68 #define bn_bn2bin(bn, buf, len) nettle_mpz_get_str_256(len, buf, bn)
69 #define bn_bin2bn(bn, buf, len) \
70  do { \
71  bn_new(bn); \
72  if (bn) \
73  nettle_mpz_set_str_256_u(bn, len, buf); \
74  } while (0)
75 #define bn_hex2bn(bn, buf, ret) \
76  do { \
77  bn_new(bn); \
78  if (bn) \
79  ret = (mpz_set_str(bn, buf, 16) == 0); \
80  } while (0)
81 #define bn_modexp(bn, y, q, p) mpz_powm(bn, y, q, p)
82 #define bn_random(bn, num_bytes) \
83  do { \
84  gmp_randstate_t rs; \
85  gmp_randinit_mt(rs); \
86  gmp_randseed_ui(rs, av_get_random_seed()); \
87  mpz_urandomb(bn, rs, num_bytes); \
88  gmp_randclear(rs); \
89  } while (0)
90 #elif CONFIG_GCRYPT
91 #define bn_new(bn) bn = gcry_mpi_new(1)
92 #define bn_free(bn) gcry_mpi_release(bn)
93 #define bn_set_word(bn, w) gcry_mpi_set_ui(bn, w)
94 #define bn_cmp(a, b) gcry_mpi_cmp(a, b)
95 #define bn_copy(to, from) gcry_mpi_set(to, from)
96 #define bn_sub_word(bn, w) gcry_mpi_sub_ui(bn, bn, w)
97 #define bn_cmp_1(bn) gcry_mpi_cmp_ui(bn, 1)
98 #define bn_num_bytes(bn) (gcry_mpi_get_nbits(bn) + 7) / 8
99 #define bn_bn2bin(bn, buf, len) gcry_mpi_print(GCRYMPI_FMT_USG, buf, len, NULL, bn)
100 #define bn_bin2bn(bn, buf, len) gcry_mpi_scan(&bn, GCRYMPI_FMT_USG, buf, len, NULL)
101 #define bn_hex2bn(bn, buf, ret) ret = (gcry_mpi_scan(&bn, GCRYMPI_FMT_HEX, buf, 0, 0) == 0)
102 #define bn_modexp(bn, y, q, p) gcry_mpi_powm(bn, y, q, p)
103 #define bn_random(bn, num_bytes) gcry_mpi_randomize(bn, num_bytes, GCRY_WEAK_RANDOM)
104 #endif
105 
106 #define MAX_BYTES 18000
107 
108 #define dh_new() av_malloc(sizeof(FF_DH))
109 
110 static FFBigNum dh_generate_key(FF_DH *dh)
111 {
112  int num_bytes;
113 
114  num_bytes = bn_num_bytes(dh->p) - 1;
115  if (num_bytes <= 0 || num_bytes > MAX_BYTES)
116  return NULL;
117 
118  bn_new(dh->priv_key);
119  if (!dh->priv_key)
120  return NULL;
121  bn_random(dh->priv_key, num_bytes);
122 
123  bn_new(dh->pub_key);
124  if (!dh->pub_key) {
125  bn_free(dh->priv_key);
126  return NULL;
127  }
128 
129  bn_modexp(dh->pub_key, dh->g, dh->priv_key, dh->p);
130 
131  return dh->pub_key;
132 }
133 
134 static int dh_compute_key(FF_DH *dh, FFBigNum pub_key_bn,
135  uint32_t pub_key_len, uint8_t *secret_key)
136 {
137  FFBigNum k;
138  int num_bytes;
139 
140  num_bytes = bn_num_bytes(dh->p);
141  if (num_bytes <= 0 || num_bytes > MAX_BYTES)
142  return -1;
143 
144  bn_new(k);
145  if (!k)
146  return -1;
147 
148  bn_modexp(k, pub_key_bn, dh->priv_key, dh->p);
149  bn_bn2bin(k, secret_key, pub_key_len);
150  bn_free(k);
151 
152  /* return the length of the shared secret key like DH_compute_key */
153  return pub_key_len;
154 }
155 
156 void ff_dh_free(FF_DH *dh)
157 {
158  bn_free(dh->p);
159  bn_free(dh->g);
160  bn_free(dh->pub_key);
161  bn_free(dh->priv_key);
162  av_free(dh);
163 }
164 #elif CONFIG_OPENSSL
165 #define bn_new(bn) bn = BN_new()
166 #define bn_free(bn) BN_free(bn)
167 #define bn_set_word(bn, w) BN_set_word(bn, w)
168 #define bn_cmp(a, b) BN_cmp(a, b)
169 #define bn_copy(to, from) BN_copy(to, from)
170 #define bn_sub_word(bn, w) BN_sub_word(bn, w)
171 #define bn_cmp_1(bn) BN_cmp(bn, BN_value_one())
172 #define bn_num_bytes(bn) BN_num_bytes(bn)
173 #define bn_bn2bin(bn, buf, len) BN_bn2bin(bn, buf)
174 #define bn_bin2bn(bn, buf, len) bn = BN_bin2bn(buf, len, 0)
175 #define bn_hex2bn(bn, buf, ret) ret = BN_hex2bn(&bn, buf)
176 #define bn_modexp(bn, y, q, p) \
177  do { \
178  BN_CTX *ctx = BN_CTX_new(); \
179  if (!ctx) \
180  return AVERROR(ENOMEM); \
181  if (!BN_mod_exp(bn, y, q, p, ctx)) { \
182  BN_CTX_free(ctx); \
183  return AVERROR(EINVAL); \
184  } \
185  BN_CTX_free(ctx); \
186  } while (0)
187 
188 #define dh_new() DH_new()
189 #define dh_generate_key(dh) DH_generate_key(dh)
190 #define dh_compute_key(dh, pub, len, secret) DH_compute_key(secret, pub, dh)
191 
192 void ff_dh_free(FF_DH *dh)
193 {
194  DH_free(dh);
195 }
196 #endif
197 
198 static int dh_is_valid_public_key(FFBigNum y, FFBigNum p, FFBigNum q)
199 {
200  FFBigNum bn = NULL;
201  int ret = AVERROR(EINVAL);
202 
203  bn_new(bn);
204  if (!bn)
205  return AVERROR(ENOMEM);
206 
207  /* y must lie in [2, p - 1] */
208  bn_set_word(bn, 1);
209  if (!bn_cmp(y, bn))
210  goto fail;
211 
212  /* bn = p - 2 */
213  bn_copy(bn, p);
214  bn_sub_word(bn, 1);
215  if (!bn_cmp(y, bn))
216  goto fail;
217 
218  /* Verify with Sophie-Germain prime
219  *
220  * This is a nice test to make sure the public key position is calculated
221  * correctly. This test will fail in about 50% of the cases if applied to
222  * random data.
223  */
224  /* y must fulfill y^q mod p = 1 */
225  bn_modexp(bn, y, q, p);
226 
227  if (bn_cmp_1(bn))
228  goto fail;
229 
230  ret = 0;
231 fail:
232  bn_free(bn);
233 
234  return ret;
235 }
236 
237 av_cold FF_DH *ff_dh_init(int key_len)
238 {
239  FF_DH *dh;
240  int ret;
241 
242  if (!(dh = dh_new()))
243  return NULL;
244 
245  bn_new(dh->g);
246  if (!dh->g)
247  goto fail;
248 
249  bn_hex2bn(dh->p, P1024, ret);
250  if (!ret)
251  goto fail;
252 
253  bn_set_word(dh->g, 2);
254  dh->length = key_len;
255 
256  return dh;
257 
258 fail:
259  ff_dh_free(dh);
260 
261  return NULL;
262 }
263 
265 {
266  int ret = 0;
267 
268  while (!ret) {
269  FFBigNum q1 = NULL;
270 
271  if (!dh_generate_key(dh))
272  return AVERROR(EINVAL);
273 
274  bn_hex2bn(q1, Q1024, ret);
275  if (!ret)
276  return AVERROR(ENOMEM);
277 
278  ret = dh_is_valid_public_key(dh->pub_key, dh->p, q1);
279  bn_free(q1);
280 
281  if (!ret) {
282  /* the public key is valid */
283  break;
284  }
285  }
286 
287  return ret;
288 }
289 
290 int ff_dh_write_public_key(FF_DH *dh, uint8_t *pub_key, int pub_key_len)
291 {
292  int len;
293 
294  /* compute the length of the public key */
295  len = bn_num_bytes(dh->pub_key);
296  if (len <= 0 || len > pub_key_len)
297  return AVERROR(EINVAL);
298 
299  /* convert the public key value into big-endian form */
300  memset(pub_key, 0, pub_key_len);
301  bn_bn2bin(dh->pub_key, pub_key + pub_key_len - len, len);
302 
303  return 0;
304 }
305 
306 int ff_dh_compute_shared_secret_key(FF_DH *dh, const uint8_t *pub_key,
307  int pub_key_len, uint8_t *secret_key)
308 {
309  FFBigNum q1 = NULL, pub_key_bn = NULL;
310  int ret;
311 
312  /* convert the big-endian form of the public key into a bignum */
313  bn_bin2bn(pub_key_bn, pub_key, pub_key_len);
314  if (!pub_key_bn)
315  return AVERROR(ENOMEM);
316 
317  /* convert the string containing a hexadecimal number into a bignum */
318  bn_hex2bn(q1, Q1024, ret);
319  if (!ret) {
320  ret = AVERROR(ENOMEM);
321  goto fail;
322  }
323 
324  /* when the public key is valid we have to compute the shared secret key */
325  if ((ret = dh_is_valid_public_key(pub_key_bn, dh->p, q1)) < 0) {
326  goto fail;
327  } else if ((ret = dh_compute_key(dh, pub_key_bn, pub_key_len,
328  secret_key)) < 0) {
329  ret = AVERROR(EINVAL);
330  goto fail;
331  }
332 
333 fail:
334  bn_free(pub_key_bn);
335  bn_free(q1);
336 
337  return ret;
338 }
339