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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 <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 #define P1024 \
42  "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1" \
43  "29024E088A67CC74020BBEA63B139B22514A08798E3404DD" \
44  "EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245" \
45  "E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED" \
46  "EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381" \
47  "FFFFFFFFFFFFFFFF"
48 
49 #define Q1024 \
50  "7FFFFFFFFFFFFFFFE487ED5110B4611A62633145C06E0E68" \
51  "948127044533E63A0105DF531D89CD9128A5043CC71A026E" \
52  "F7CA8CD9E69D218D98158536F92F8A1BA7F09AB6B6A8E122" \
53  "F242DABB312F3F637A262174D31BF6B585FFAE5B7A035BF6" \
54  "F71C35FDAD44CFD2D74F9208BE258FF324943328F67329C0" \
55  "FFFFFFFFFFFFFFFF"
56 
57 #if CONFIG_GMP
58 #define bn_new(bn) \
59  do { \
60  bn = av_malloc(sizeof(*bn)); \
61  if (bn) \
62  mpz_init2(bn, 1); \
63  } while (0)
64 #define bn_free(bn) \
65  do { \
66  mpz_clear(bn); \
67  av_free(bn); \
68  } while (0)
69 #define bn_set_word(bn, w) mpz_set_ui(bn, w)
70 #define bn_cmp(a, b) mpz_cmp(a, b)
71 #define bn_copy(to, from) mpz_set(to, from)
72 #define bn_sub_word(bn, w) mpz_sub_ui(bn, bn, w)
73 #define bn_cmp_1(bn) mpz_cmp_ui(bn, 1)
74 #define bn_num_bytes(bn) (mpz_sizeinbase(bn, 2) + 7) / 8
75 #define bn_bn2bin(bn, buf, len) \
76  do { \
77  memset(buf, 0, len); \
78  if (bn_num_bytes(bn) <= len) \
79  mpz_export(buf, NULL, 1, 1, 0, 0, bn); \
80  } while (0)
81 #define bn_bin2bn(bn, buf, len) \
82  do { \
83  bn_new(bn); \
84  if (bn) \
85  mpz_import(bn, len, 1, 1, 0, 0, buf); \
86  } while (0)
87 #define bn_hex2bn(bn, buf, ret) \
88  do { \
89  bn_new(bn); \
90  if (bn) \
91  ret = (mpz_set_str(bn, buf, 16) == 0); \
92  else \
93  ret = 1; \
94  } while (0)
95 #define bn_random(bn, num_bits) \
96  do { \
97  int bits = num_bits; \
98  mpz_set_ui(bn, 0); \
99  for (bits = num_bits; bits > 0; bits -= 32) { \
100  mpz_mul_2exp(bn, bn, 32); \
101  mpz_add_ui(bn, bn, av_get_random_seed()); \
102  } \
103  mpz_fdiv_r_2exp(bn, bn, num_bits); \
104  } while (0)
105 static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
106 {
107  mpz_powm(bn, y, q, p);
108  return 0;
109 }
110 #elif CONFIG_GCRYPT
111 #define bn_new(bn) \
112  do { \
113  if (!gcry_control(GCRYCTL_INITIALIZATION_FINISHED_P)) { \
114  if (!gcry_check_version("1.5.4")) \
115  return AVERROR(EINVAL); \
116  gcry_control(GCRYCTL_DISABLE_SECMEM, 0); \
117  gcry_control(GCRYCTL_INITIALIZATION_FINISHED, 0); \
118  } \
119  bn = gcry_mpi_new(1); \
120  } while (0)
121 #define bn_free(bn) gcry_mpi_release(bn)
122 #define bn_set_word(bn, w) gcry_mpi_set_ui(bn, w)
123 #define bn_cmp(a, b) gcry_mpi_cmp(a, b)
124 #define bn_copy(to, from) gcry_mpi_set(to, from)
125 #define bn_sub_word(bn, w) gcry_mpi_sub_ui(bn, bn, w)
126 #define bn_cmp_1(bn) gcry_mpi_cmp_ui(bn, 1)
127 #define bn_num_bytes(bn) (gcry_mpi_get_nbits(bn) + 7) / 8
128 #define bn_bn2bin(bn, buf, len) gcry_mpi_print(GCRYMPI_FMT_USG, buf, len, NULL, bn)
129 #define bn_bin2bn(bn, buf, len) gcry_mpi_scan(&bn, GCRYMPI_FMT_USG, buf, len, NULL)
130 #define bn_hex2bn(bn, buf, ret) ret = (gcry_mpi_scan(&bn, GCRYMPI_FMT_HEX, buf, 0, 0) == 0)
131 #define bn_random(bn, num_bits) gcry_mpi_randomize(bn, num_bits, GCRY_WEAK_RANDOM)
132 static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
133 {
134  gcry_mpi_powm(bn, y, q, p);
135  return 0;
136 }
137 #elif CONFIG_OPENSSL
138 #define bn_new(bn) bn = BN_new()
139 #define bn_free(bn) BN_free(bn)
140 #define bn_set_word(bn, w) BN_set_word(bn, w)
141 #define bn_cmp(a, b) BN_cmp(a, b)
142 #define bn_copy(to, from) BN_copy(to, from)
143 #define bn_sub_word(bn, w) BN_sub_word(bn, w)
144 #define bn_cmp_1(bn) BN_cmp(bn, BN_value_one())
145 #define bn_num_bytes(bn) BN_num_bytes(bn)
146 #define bn_bn2bin(bn, buf, len) BN_bn2bin(bn, buf)
147 #define bn_bin2bn(bn, buf, len) bn = BN_bin2bn(buf, len, 0)
148 #define bn_hex2bn(bn, buf, ret) ret = BN_hex2bn(&bn, buf)
149 #define bn_random(bn, num_bits) BN_rand(bn, num_bits, 0, 0)
150 static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
151 {
152  BN_CTX *ctx = BN_CTX_new();
153  if (!ctx)
154  return AVERROR(ENOMEM);
155  if (!BN_mod_exp(bn, y, q, p, ctx)) {
156  BN_CTX_free(ctx);
157  return AVERROR(EINVAL);
158  }
159  BN_CTX_free(ctx);
160  return 0;
161 }
162 #endif
163 
164 #define MAX_BYTES 18000
165 
166 #define dh_new() av_mallocz(sizeof(FF_DH))
167 
168 static FFBigNum dh_generate_key(FF_DH *dh)
169 {
170  int num_bytes;
171 
172  num_bytes = bn_num_bytes(dh->p) - 1;
173  if (num_bytes <= 0 || num_bytes > MAX_BYTES)
174  return NULL;
175 
176  bn_new(dh->priv_key);
177  if (!dh->priv_key)
178  return NULL;
179  bn_random(dh->priv_key, 8 * num_bytes);
180 
181  bn_new(dh->pub_key);
182  if (!dh->pub_key) {
183  bn_free(dh->priv_key);
184  return NULL;
185  }
186 
187  if (bn_modexp(dh->pub_key, dh->g, dh->priv_key, dh->p) < 0)
188  return NULL;
189 
190  return dh->pub_key;
191 }
192 
193 static int dh_compute_key(FF_DH *dh, FFBigNum pub_key_bn,
194  uint32_t secret_key_len, uint8_t *secret_key)
195 {
196  FFBigNum k;
197  int ret;
198 
199  bn_new(k);
200  if (!k)
201  return -1;
202 
203  if ((ret = bn_modexp(k, pub_key_bn, dh->priv_key, dh->p)) < 0) {
204  bn_free(k);
205  return ret;
206  }
207  bn_bn2bin(k, secret_key, secret_key_len);
208  bn_free(k);
209 
210  /* return the length of the shared secret key like DH_compute_key */
211  return secret_key_len;
212 }
213 
214 void ff_dh_free(FF_DH *dh)
215 {
216  if (!dh)
217  return;
218  bn_free(dh->p);
219  bn_free(dh->g);
220  bn_free(dh->pub_key);
221  bn_free(dh->priv_key);
222  av_free(dh);
223 }
224 
225 static int dh_is_valid_public_key(FFBigNum y, FFBigNum p, FFBigNum q)
226 {
227  FFBigNum bn = NULL;
228  int ret = AVERROR(EINVAL);
229 
230  bn_new(bn);
231  if (!bn)
232  return AVERROR(ENOMEM);
233 
234  /* y must lie in [2, p - 1] */
235  bn_set_word(bn, 1);
236  if (!bn_cmp(y, bn))
237  goto fail;
238 
239  /* bn = p - 2 */
240  bn_copy(bn, p);
241  bn_sub_word(bn, 1);
242  if (!bn_cmp(y, bn))
243  goto fail;
244 
245  /* Verify with Sophie-Germain prime
246  *
247  * This is a nice test to make sure the public key position is calculated
248  * correctly. This test will fail in about 50% of the cases if applied to
249  * random data.
250  */
251  /* y must fulfill y^q mod p = 1 */
252  if ((ret = bn_modexp(bn, y, q, p)) < 0)
253  goto fail;
254 
255  ret = AVERROR(EINVAL);
256  if (bn_cmp_1(bn))
257  goto fail;
258 
259  ret = 0;
260 fail:
261  bn_free(bn);
262 
263  return ret;
264 }
265 
266 av_cold FF_DH *ff_dh_init(int key_len)
267 {
268  FF_DH *dh;
269  int ret;
270 
271  if (!(dh = dh_new()))
272  return NULL;
273 
274  bn_new(dh->g);
275  if (!dh->g)
276  goto fail;
277 
278  bn_hex2bn(dh->p, P1024, ret);
279  if (!ret)
280  goto fail;
281 
282  bn_set_word(dh->g, 2);
283  dh->length = key_len;
284 
285  return dh;
286 
287 fail:
288  ff_dh_free(dh);
289 
290  return NULL;
291 }
292 
294 {
295  int ret = 0;
296 
297  while (!ret) {
298  FFBigNum q1 = NULL;
299 
300  if (!dh_generate_key(dh))
301  return AVERROR(EINVAL);
302 
303  bn_hex2bn(q1, Q1024, ret);
304  if (!ret)
305  return AVERROR(ENOMEM);
306 
307  ret = dh_is_valid_public_key(dh->pub_key, dh->p, q1);
308  bn_free(q1);
309 
310  if (!ret) {
311  /* the public key is valid */
312  break;
313  }
314  }
315 
316  return ret;
317 }
318 
319 int ff_dh_write_public_key(FF_DH *dh, uint8_t *pub_key, int pub_key_len)
320 {
321  int len;
322 
323  /* compute the length of the public key */
324  len = bn_num_bytes(dh->pub_key);
325  if (len <= 0 || len > pub_key_len)
326  return AVERROR(EINVAL);
327 
328  /* convert the public key value into big-endian form */
329  memset(pub_key, 0, pub_key_len);
330  bn_bn2bin(dh->pub_key, pub_key + pub_key_len - len, len);
331 
332  return 0;
333 }
334 
336  int pub_key_len, uint8_t *secret_key,
337  int secret_key_len)
338 {
339  FFBigNum q1 = NULL, pub_key_bn = NULL;
340  int ret;
341 
342  /* convert the big-endian form of the public key into a bignum */
343  bn_bin2bn(pub_key_bn, pub_key, pub_key_len);
344  if (!pub_key_bn)
345  return AVERROR(ENOMEM);
346 
347  /* convert the string containing a hexadecimal number into a bignum */
348  bn_hex2bn(q1, Q1024, ret);
349  if (!ret) {
350  ret = AVERROR(ENOMEM);
351  goto fail;
352  }
353 
354  /* when the public key is valid we have to compute the shared secret key */
355  if ((ret = dh_is_valid_public_key(pub_key_bn, dh->p, q1)) < 0) {
356  goto fail;
357  } else if ((ret = dh_compute_key(dh, pub_key_bn, secret_key_len,
358  secret_key)) < 0) {
359  ret = AVERROR(EINVAL);
360  goto fail;
361  }
362 
363 fail:
364  bn_free(pub_key_bn);
365  bn_free(q1);
366 
367  return ret;
368 }
uint32_t p[AV_BF_ROUNDS+2]
Definition: blowfish.h:36
#define NULL
Definition: coverity.c:32
int ff_dh_write_public_key(FF_DH *dh, uint8_t *pub_key, int pub_key_len)
Write the public key into the given buffer.
Definition: rtmpdh.c:319
Definition: rtmpdh.h:45
static int dh_is_valid_public_key(FFBigNum y, FFBigNum p, FFBigNum q)
Definition: rtmpdh.c:225
Memory handling functions.
int ff_dh_compute_shared_secret_key(FF_DH *dh, const uint8_t *pub_key, int pub_key_len, uint8_t *secret_key, int secret_key_len)
Compute the shared secret key from the private FF_DH value and the other party's public value...
Definition: rtmpdh.c:335
void ff_dh_free(FF_DH *dh)
Free a Diffie-Hellmann context.
Definition: rtmpdh.c:214
#define P1024
Definition: rtmpdh.c:41
FFBigNum priv_key
Definition: rtmpdh.h:49
static const uint8_t q1[256]
Definition: twofish.c:96
Macro definitions for various function/variable attributes.
uint8_t
#define av_cold
Definition: attributes.h:82
int ff_dh_generate_public_key(FF_DH *dh)
Generate a public key.
Definition: rtmpdh.c:293
error code definitions
FFBigNum p
Definition: rtmpdh.h:46
#define AVERROR(e)
Definition: error.h:43
#define fail()
Definition: checkasm.h:89
AVFormatContext * ctx
Definition: movenc.c:48
static int dh_compute_key(FF_DH *dh, FFBigNum pub_key_bn, uint32_t secret_key_len, uint8_t *secret_key)
Definition: rtmpdh.c:193
FFBigNum g
Definition: rtmpdh.h:47
#define dh_new()
Definition: rtmpdh.c:166
#define Q1024
Definition: rtmpdh.c:49
#define MAX_BYTES
Definition: rtmpdh.c:164
long length
Definition: rtmpdh.h:50
av_cold FF_DH * ff_dh_init(int key_len)
Initialize a Diffie-Hellmann context.
Definition: rtmpdh.c:266
FFBigNum pub_key
Definition: rtmpdh.h:48
#define av_free(p)
int len
static FFBigNum dh_generate_key(FF_DH *dh)
Definition: rtmpdh.c:168