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)
bn_modexp(FFBigNum bn,FFBigNum y,FFBigNum q,FFBigNum p)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 return AVERROR(EINVAL); \
121 gcry_control(GCRYCTL_DISABLE_SECMEM, 0); \
122 gcry_control(GCRYCTL_INITIALIZATION_FINISHED, 0); \
123 } \
124 bn = gcry_mpi_new(1); \
125 } while (0)
126 #define bn_free(bn) gcry_mpi_release(bn)
127 #define bn_set_word(bn, w) gcry_mpi_set_ui(bn, w)
128 #define bn_cmp(a, b) gcry_mpi_cmp(a, b)
129 #define bn_copy(to, from) gcry_mpi_set(to, from)
130 #define bn_sub_word(bn, w) gcry_mpi_sub_ui(bn, bn, w)
131 #define bn_cmp_1(bn) gcry_mpi_cmp_ui(bn, 1)
132 #define bn_num_bytes(bn) (gcry_mpi_get_nbits(bn) + 7) / 8
133 #define bn_bn2bin(bn, buf, len) gcry_mpi_print(GCRYMPI_FMT_USG, buf, len, NULL, bn)
134 #define bn_bin2bn(bn, buf, len) gcry_mpi_scan(&bn, GCRYMPI_FMT_USG, buf, len, NULL)
135 #define bn_hex2bn(bn, buf, ret) ret = (gcry_mpi_scan(&bn, GCRYMPI_FMT_HEX, buf, 0, 0) == 0)
136 #define bn_random(bn, num_bits) gcry_mpi_randomize(bn, num_bits, GCRY_WEAK_RANDOM)
bn_modexp(FFBigNum bn,FFBigNum y,FFBigNum q,FFBigNum p)137 static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
138 {
139 gcry_mpi_powm(bn, y, q, p);
140 return 0;
141 }
142 #elif CONFIG_OPENSSL
143 #define bn_new(bn) bn = BN_new()
144 #define bn_free(bn) BN_free(bn)
145 #define bn_set_word(bn, w) BN_set_word(bn, w)
146 #define bn_cmp(a, b) BN_cmp(a, b)
147 #define bn_copy(to, from) BN_copy(to, from)
148 #define bn_sub_word(bn, w) BN_sub_word(bn, w)
149 #define bn_cmp_1(bn) BN_cmp(bn, BN_value_one())
150 #define bn_num_bytes(bn) BN_num_bytes(bn)
151 #define bn_bn2bin(bn, buf, len) BN_bn2bin(bn, buf)
152 #define bn_bin2bn(bn, buf, len) bn = BN_bin2bn(buf, len, 0)
153 #define bn_hex2bn(bn, buf, ret) ret = BN_hex2bn(&bn, buf)
154 #define bn_random(bn, num_bits) BN_rand(bn, num_bits, 0, 0)
bn_modexp(FFBigNum bn,FFBigNum y,FFBigNum q,FFBigNum p)155 static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
156 {
157 BN_CTX *ctx = BN_CTX_new();
158 if (!ctx)
159 return AVERROR(ENOMEM);
160 if (!BN_mod_exp(bn, y, q, p, ctx)) {
161 BN_CTX_free(ctx);
162 return AVERROR(EINVAL);
163 }
164 BN_CTX_free(ctx);
165 return 0;
166 }
167 #elif CONFIG_MBEDTLS
168 #define bn_new(bn) \
169 do { \
170 bn = av_malloc(sizeof(*bn)); \
171 if (bn) \
172 mbedtls_mpi_init(bn); \
173 } while (0)
174 #define bn_free(bn) \
175 do { \
176 mbedtls_mpi_free(bn); \
177 av_free(bn); \
178 } while (0)
179 #define bn_set_word(bn, w) mbedtls_mpi_lset(bn, w)
180 #define bn_cmp(a, b) mbedtls_mpi_cmp_mpi(a, b)
181 #define bn_copy(to, from) mbedtls_mpi_copy(to, from)
182 #define bn_sub_word(bn, w) mbedtls_mpi_sub_int(bn, bn, w)
183 #define bn_cmp_1(bn) mbedtls_mpi_cmp_int(bn, 1)
184 #define bn_num_bytes(bn) (mbedtls_mpi_bitlen(bn) + 7) / 8
185 #define bn_bn2bin(bn, buf, len) mbedtls_mpi_write_binary(bn, buf, len)
186 #define bn_bin2bn(bn, buf, len) \
187 do { \
188 bn_new(bn); \
189 if (bn) \
190 mbedtls_mpi_read_binary(bn, buf, len); \
191 } while (0)
192 #define bn_hex2bn(bn, buf, ret) \
193 do { \
194 bn_new(bn); \
195 if (bn) \
196 ret = (mbedtls_mpi_read_string(bn, 16, buf) == 0); \
197 else \
198 ret = 1; \
199 } while (0)
200 #define bn_random(bn, num_bits) \
201 do { \
202 mbedtls_entropy_context entropy_ctx; \
203 mbedtls_ctr_drbg_context ctr_drbg_ctx; \
204 \
205 mbedtls_entropy_init(&entropy_ctx); \
206 mbedtls_ctr_drbg_init(&ctr_drbg_ctx); \
207 mbedtls_ctr_drbg_seed(&ctr_drbg_ctx, \
208 mbedtls_entropy_func, \
209 &entropy_ctx, \
210 NULL, 0); \
211 mbedtls_mpi_fill_random(bn, (num_bits + 7) / 8, mbedtls_ctr_drbg_random, &ctr_drbg_ctx); \
212 mbedtls_ctr_drbg_free(&ctr_drbg_ctx); \
213 mbedtls_entropy_free(&entropy_ctx); \
214 } while (0)
215 #define bn_modexp(bn, y, q, p) mbedtls_mpi_exp_mod(bn, y, q, p, 0)
216
217 #endif
218
219 #define MAX_BYTES 18000
220
221 #define dh_new() av_mallocz(sizeof(FF_DH))
222
dh_generate_key(FF_DH * dh)223 static FFBigNum dh_generate_key(FF_DH *dh)
224 {
225 int num_bytes;
226
227 num_bytes = bn_num_bytes(dh->p) - 1;
228 if (num_bytes <= 0 || num_bytes > MAX_BYTES)
229 return NULL;
230
231 bn_new(dh->priv_key);
232 if (!dh->priv_key)
233 return NULL;
234 bn_random(dh->priv_key, 8 * num_bytes);
235
236 bn_new(dh->pub_key);
237 if (!dh->pub_key) {
238 bn_free(dh->priv_key);
239 return NULL;
240 }
241
242 if (bn_modexp(dh->pub_key, dh->g, dh->priv_key, dh->p) < 0)
243 return NULL;
244
245 return dh->pub_key;
246 }
247
dh_compute_key(FF_DH * dh,FFBigNum pub_key_bn,uint32_t secret_key_len,uint8_t * secret_key)248 static int dh_compute_key(FF_DH *dh, FFBigNum pub_key_bn,
249 uint32_t secret_key_len, uint8_t *secret_key)
250 {
251 FFBigNum k;
252 int ret;
253
254 bn_new(k);
255 if (!k)
256 return -1;
257
258 if ((ret = bn_modexp(k, pub_key_bn, dh->priv_key, dh->p)) < 0) {
259 bn_free(k);
260 return ret;
261 }
262 bn_bn2bin(k, secret_key, secret_key_len);
263 bn_free(k);
264
265 /* return the length of the shared secret key like DH_compute_key */
266 return secret_key_len;
267 }
268
ff_dh_free(FF_DH * dh)269 void ff_dh_free(FF_DH *dh)
270 {
271 if (!dh)
272 return;
273 bn_free(dh->p);
274 bn_free(dh->g);
275 bn_free(dh->pub_key);
276 bn_free(dh->priv_key);
277 av_free(dh);
278 }
279
dh_is_valid_public_key(FFBigNum y,FFBigNum p,FFBigNum q)280 static int dh_is_valid_public_key(FFBigNum y, FFBigNum p, FFBigNum q)
281 {
282 FFBigNum bn = NULL;
283 int ret = AVERROR(EINVAL);
284
285 bn_new(bn);
286 if (!bn)
287 return AVERROR(ENOMEM);
288
289 /* y must lie in [2, p - 1] */
290 bn_set_word(bn, 1);
291 if (!bn_cmp(y, bn))
292 goto fail;
293
294 /* bn = p - 2 */
295 bn_copy(bn, p);
296 bn_sub_word(bn, 1);
297 if (!bn_cmp(y, bn))
298 goto fail;
299
300 /* Verify with Sophie-Germain prime
301 *
302 * This is a nice test to make sure the public key position is calculated
303 * correctly. This test will fail in about 50% of the cases if applied to
304 * random data.
305 */
306 /* y must fulfill y^q mod p = 1 */
307 if ((ret = bn_modexp(bn, y, q, p)) < 0)
308 goto fail;
309
310 ret = AVERROR(EINVAL);
311 if (bn_cmp_1(bn))
312 goto fail;
313
314 ret = 0;
315 fail:
316 bn_free(bn);
317
318 return ret;
319 }
320
ff_dh_init(int key_len)321 av_cold FF_DH *ff_dh_init(int key_len)
322 {
323 FF_DH *dh;
324 int ret;
325
326 if (!(dh = dh_new()))
327 return NULL;
328
329 bn_new(dh->g);
330 if (!dh->g)
331 goto fail;
332
333 bn_hex2bn(dh->p, P1024, ret);
334 if (!ret)
335 goto fail;
336
337 bn_set_word(dh->g, 2);
338 dh->length = key_len;
339
340 return dh;
341
342 fail:
343 ff_dh_free(dh);
344
345 return NULL;
346 }
347
ff_dh_generate_public_key(FF_DH * dh)348 int ff_dh_generate_public_key(FF_DH *dh)
349 {
350 int ret = 0;
351
352 while (!ret) {
353 FFBigNum q1 = NULL;
354
355 if (!dh_generate_key(dh))
356 return AVERROR(EINVAL);
357
358 bn_hex2bn(q1, Q1024, ret);
359 if (!ret)
360 return AVERROR(ENOMEM);
361
362 ret = dh_is_valid_public_key(dh->pub_key, dh->p, q1);
363 bn_free(q1);
364
365 if (!ret) {
366 /* the public key is valid */
367 break;
368 }
369 }
370
371 return ret;
372 }
373
ff_dh_write_public_key(FF_DH * dh,uint8_t * pub_key,int pub_key_len)374 int ff_dh_write_public_key(FF_DH *dh, uint8_t *pub_key, int pub_key_len)
375 {
376 int len;
377
378 /* compute the length of the public key */
379 len = bn_num_bytes(dh->pub_key);
380 if (len <= 0 || len > pub_key_len)
381 return AVERROR(EINVAL);
382
383 /* convert the public key value into big-endian form */
384 memset(pub_key, 0, pub_key_len);
385 bn_bn2bin(dh->pub_key, pub_key + pub_key_len - len, len);
386
387 return 0;
388 }
389
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)390 int ff_dh_compute_shared_secret_key(FF_DH *dh, const uint8_t *pub_key,
391 int pub_key_len, uint8_t *secret_key,
392 int secret_key_len)
393 {
394 FFBigNum q1 = NULL, pub_key_bn = NULL;
395 int ret;
396
397 /* convert the big-endian form of the public key into a bignum */
398 bn_bin2bn(pub_key_bn, pub_key, pub_key_len);
399 if (!pub_key_bn)
400 return AVERROR(ENOMEM);
401
402 /* convert the string containing a hexadecimal number into a bignum */
403 bn_hex2bn(q1, Q1024, ret);
404 if (!ret) {
405 ret = AVERROR(ENOMEM);
406 goto fail;
407 }
408
409 /* when the public key is valid we have to compute the shared secret key */
410 if ((ret = dh_is_valid_public_key(pub_key_bn, dh->p, q1)) < 0) {
411 goto fail;
412 } else if ((ret = dh_compute_key(dh, pub_key_bn, secret_key_len,
413 secret_key)) < 0) {
414 ret = AVERROR(EINVAL);
415 goto fail;
416 }
417
418 fail:
419 bn_free(pub_key_bn);
420 bn_free(q1);
421
422 return ret;
423 }
424