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
110static 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
134static 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
156void 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
192void ff_dh_free(FF_DH *dh)
193{
194    DH_free(dh);
195}
196#endif
197
198static 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;
231fail:
232    bn_free(bn);
233
234    return ret;
235}
236
237av_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
258fail:
259    ff_dh_free(dh);
260
261    return NULL;
262}
263
264int ff_dh_generate_public_key(FF_DH *dh)
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
290int 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
306int 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
333fail:
334    bn_free(pub_key_bn);
335    bn_free(q1);
336
337    return ret;
338}
339
340