0593eac943ffd875c2375205ceec041d6ac9a5f3
[libav.git] / 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 Libav.
8 *
9 * Libav 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 * Libav 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 Libav; 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_OPENSSL
111 #define bn_new(bn) bn = BN_new()
112 #define bn_free(bn) BN_free(bn)
113 #define bn_set_word(bn, w) BN_set_word(bn, w)
114 #define bn_cmp(a, b) BN_cmp(a, b)
115 #define bn_copy(to, from) BN_copy(to, from)
116 #define bn_sub_word(bn, w) BN_sub_word(bn, w)
117 #define bn_cmp_1(bn) BN_cmp(bn, BN_value_one())
118 #define bn_num_bytes(bn) BN_num_bytes(bn)
119 #define bn_bn2bin(bn, buf, len) BN_bn2bin(bn, buf)
120 #define bn_bin2bn(bn, buf, len) bn = BN_bin2bn(buf, len, 0)
121 #define bn_hex2bn(bn, buf, ret) ret = BN_hex2bn(&bn, buf)
122 #define bn_random(bn, num_bits) BN_rand(bn, num_bits, 0, 0)
123 static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
124 {
125 BN_CTX *ctx = BN_CTX_new();
126 if (!ctx)
127 return AVERROR(ENOMEM);
128 if (!BN_mod_exp(bn, y, q, p, ctx)) {
129 BN_CTX_free(ctx);
130 return AVERROR(EINVAL);
131 }
132 BN_CTX_free(ctx);
133 return 0;
134 }
135 #endif
136
137 #define MAX_BYTES 18000
138
139 #define dh_new() av_mallocz(sizeof(FF_DH))
140
141 static FFBigNum dh_generate_key(FF_DH *dh)
142 {
143 int num_bytes;
144
145 num_bytes = bn_num_bytes(dh->p) - 1;
146 if (num_bytes <= 0 || num_bytes > MAX_BYTES)
147 return NULL;
148
149 bn_new(dh->priv_key);
150 if (!dh->priv_key)
151 return NULL;
152 bn_random(dh->priv_key, 8 * num_bytes);
153
154 bn_new(dh->pub_key);
155 if (!dh->pub_key) {
156 bn_free(dh->priv_key);
157 return NULL;
158 }
159
160 if (bn_modexp(dh->pub_key, dh->g, dh->priv_key, dh->p) < 0)
161 return NULL;
162
163 return dh->pub_key;
164 }
165
166 static int dh_compute_key(FF_DH *dh, FFBigNum pub_key_bn,
167 uint32_t secret_key_len, uint8_t *secret_key)
168 {
169 FFBigNum k;
170 int ret;
171
172 bn_new(k);
173 if (!k)
174 return -1;
175
176 if ((ret = bn_modexp(k, pub_key_bn, dh->priv_key, dh->p)) < 0) {
177 bn_free(k);
178 return ret;
179 }
180 bn_bn2bin(k, secret_key, secret_key_len);
181 bn_free(k);
182
183 /* return the length of the shared secret key like DH_compute_key */
184 return secret_key_len;
185 }
186
187 void ff_dh_free(FF_DH *dh)
188 {
189 if (!dh)
190 return;
191 bn_free(dh->p);
192 bn_free(dh->g);
193 bn_free(dh->pub_key);
194 bn_free(dh->priv_key);
195 av_free(dh);
196 }
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 if ((ret = bn_modexp(bn, y, q, p)) < 0)
226 goto fail;
227
228 ret = AVERROR(EINVAL);
229 if (bn_cmp_1(bn))
230 goto fail;
231
232 ret = 0;
233 fail:
234 bn_free(bn);
235
236 return ret;
237 }
238
239 av_cold FF_DH *ff_dh_init(int key_len)
240 {
241 FF_DH *dh;
242 int ret;
243
244 if (!(dh = dh_new()))
245 return NULL;
246
247 bn_new(dh->g);
248 if (!dh->g)
249 goto fail;
250
251 bn_hex2bn(dh->p, P1024, ret);
252 if (!ret)
253 goto fail;
254
255 bn_set_word(dh->g, 2);
256 dh->length = key_len;
257
258 return dh;
259
260 fail:
261 ff_dh_free(dh);
262
263 return NULL;
264 }
265
266 int ff_dh_generate_public_key(FF_DH *dh)
267 {
268 int ret = 0;
269
270 while (!ret) {
271 FFBigNum q1 = NULL;
272
273 if (!dh_generate_key(dh))
274 return AVERROR(EINVAL);
275
276 bn_hex2bn(q1, Q1024, ret);
277 if (!ret)
278 return AVERROR(ENOMEM);
279
280 ret = dh_is_valid_public_key(dh->pub_key, dh->p, q1);
281 bn_free(q1);
282
283 if (!ret) {
284 /* the public key is valid */
285 break;
286 }
287 }
288
289 return ret;
290 }
291
292 int ff_dh_write_public_key(FF_DH *dh, uint8_t *pub_key, int pub_key_len)
293 {
294 int len;
295
296 /* compute the length of the public key */
297 len = bn_num_bytes(dh->pub_key);
298 if (len <= 0 || len > pub_key_len)
299 return AVERROR(EINVAL);
300
301 /* convert the public key value into big-endian form */
302 memset(pub_key, 0, pub_key_len);
303 bn_bn2bin(dh->pub_key, pub_key + pub_key_len - len, len);
304
305 return 0;
306 }
307
308 int ff_dh_compute_shared_secret_key(FF_DH *dh, const uint8_t *pub_key,
309 int pub_key_len, uint8_t *secret_key,
310 int secret_key_len)
311 {
312 FFBigNum q1 = NULL, pub_key_bn = NULL;
313 int ret;
314
315 /* convert the big-endian form of the public key into a bignum */
316 bn_bin2bn(pub_key_bn, pub_key, pub_key_len);
317 if (!pub_key_bn)
318 return AVERROR(ENOMEM);
319
320 /* convert the string containing a hexadecimal number into a bignum */
321 bn_hex2bn(q1, Q1024, ret);
322 if (!ret) {
323 ret = AVERROR(ENOMEM);
324 goto fail;
325 }
326
327 /* when the public key is valid we have to compute the shared secret key */
328 if ((ret = dh_is_valid_public_key(pub_key_bn, dh->p, q1)) < 0) {
329 goto fail;
330 } else if ((ret = dh_compute_key(dh, pub_key_bn, secret_key_len,
331 secret_key)) < 0) {
332 ret = AVERROR(EINVAL);
333 goto fail;
334 }
335
336 fail:
337 bn_free(pub_key_bn);
338 bn_free(q1);
339
340 return ret;
341 }