e054fcc9b6b6a73f42f6fe5798b3ca4de44035e7
[libav.git] / libavformat / srtp.c
1 /*
2 * SRTP encryption/decryption
3 * Copyright (c) 2012 Martin Storsjo
4 *
5 * This file is part of Libav.
6 *
7 * Libav is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * Libav is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with Libav; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22 #include "libavutil/base64.h"
23 #include "libavutil/aes.h"
24 #include "libavutil/hmac.h"
25 #include "libavutil/intreadwrite.h"
26 #include "libavutil/log.h"
27 #include "rtp.h"
28 #include "rtpdec.h"
29 #include "srtp.h"
30
31 void ff_srtp_free(struct SRTPContext *s)
32 {
33 if (!s)
34 return;
35 av_freep(&s->aes);
36 if (s->hmac)
37 av_hmac_free(s->hmac);
38 s->hmac = NULL;
39 }
40
41 static void encrypt_counter(struct AVAES *aes, uint8_t *iv, uint8_t *outbuf,
42 int outlen)
43 {
44 int i, j, outpos;
45 for (i = 0, outpos = 0; outpos < outlen; i++) {
46 uint8_t keystream[16];
47 AV_WB16(&iv[14], i);
48 av_aes_crypt(aes, keystream, iv, 1, NULL, 0);
49 for (j = 0; j < 16 && outpos < outlen; j++, outpos++)
50 outbuf[outpos] ^= keystream[j];
51 }
52 }
53
54 static void derive_key(struct AVAES *aes, const uint8_t *salt, int label,
55 uint8_t *out, int outlen)
56 {
57 uint8_t input[16] = { 0 };
58 memcpy(input, salt, 14);
59 // Key derivation rate assumed to be zero
60 input[14 - 7] ^= label;
61 memset(out, 0, outlen);
62 encrypt_counter(aes, input, out, outlen);
63 }
64
65 int ff_srtp_set_crypto(struct SRTPContext *s, const char *suite,
66 const char *params)
67 {
68 uint8_t buf[30];
69
70 ff_srtp_free(s);
71
72 // RFC 4568
73 if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_80") ||
74 !strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_80")) {
75 s->rtp_hmac_size = s->rtcp_hmac_size = 10;
76 } else if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_32")) {
77 s->rtp_hmac_size = s->rtcp_hmac_size = 4;
78 } else if (!strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_32")) {
79 // RFC 5764 section 4.1.2
80 s->rtp_hmac_size = 4;
81 s->rtcp_hmac_size = 10;
82 } else {
83 av_log(NULL, AV_LOG_WARNING, "SRTP Crypto suite %s not supported\n",
84 suite);
85 return AVERROR(EINVAL);
86 }
87 if (av_base64_decode(buf, params, sizeof(buf)) != sizeof(buf)) {
88 av_log(NULL, AV_LOG_WARNING, "Incorrect amount of SRTP params\n");
89 return AVERROR(EINVAL);
90 }
91 // MKI and lifetime not handled yet
92 s->aes = av_aes_alloc();
93 s->hmac = av_hmac_alloc(AV_HMAC_SHA1);
94 if (!s->aes || !s->hmac)
95 return AVERROR(ENOMEM);
96 memcpy(s->master_key, buf, 16);
97 memcpy(s->master_salt, buf + 16, 14);
98
99 // RFC 3711
100 av_aes_init(s->aes, s->master_key, 128, 0);
101
102 derive_key(s->aes, s->master_salt, 0x00, s->rtp_key, sizeof(s->rtp_key));
103 derive_key(s->aes, s->master_salt, 0x02, s->rtp_salt, sizeof(s->rtp_salt));
104 derive_key(s->aes, s->master_salt, 0x01, s->rtp_auth, sizeof(s->rtp_auth));
105
106 derive_key(s->aes, s->master_salt, 0x03, s->rtcp_key, sizeof(s->rtcp_key));
107 derive_key(s->aes, s->master_salt, 0x05, s->rtcp_salt, sizeof(s->rtcp_salt));
108 derive_key(s->aes, s->master_salt, 0x04, s->rtcp_auth, sizeof(s->rtcp_auth));
109 return 0;
110 }
111
112 static void create_iv(uint8_t *iv, const uint8_t *salt, uint64_t index,
113 uint32_t ssrc)
114 {
115 uint8_t indexbuf[8];
116 int i;
117 memset(iv, 0, 16);
118 AV_WB32(&iv[4], ssrc);
119 AV_WB64(indexbuf, index);
120 for (i = 0; i < 8; i++) // index << 16
121 iv[6 + i] ^= indexbuf[i];
122 for (i = 0; i < 14; i++)
123 iv[i] ^= salt[i];
124 }
125
126 int ff_srtp_decrypt(struct SRTPContext *s, uint8_t *buf, int *lenptr)
127 {
128 uint8_t iv[16] = { 0 }, hmac[20];
129 int len = *lenptr;
130 int av_uninit(seq_largest);
131 uint32_t ssrc, av_uninit(roc);
132 uint64_t index;
133 int rtcp, hmac_size;
134
135 // TODO: Missing replay protection
136
137 if (len < 2)
138 return AVERROR_INVALIDDATA;
139
140 rtcp = RTP_PT_IS_RTCP(buf[1]);
141 hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size;
142
143 if (len < hmac_size)
144 return AVERROR_INVALIDDATA;
145
146 // Authentication HMAC
147 av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth));
148 // If MKI is used, this should exclude the MKI as well
149 av_hmac_update(s->hmac, buf, len - hmac_size);
150
151 if (!rtcp) {
152 int seq = AV_RB16(buf + 2);
153 uint32_t v;
154 uint8_t rocbuf[4];
155
156 // RFC 3711 section 3.3.1, appendix A
157 seq_largest = s->seq_initialized ? s->seq_largest : seq;
158 v = roc = s->roc;
159 if (seq_largest < 32768) {
160 if (seq - seq_largest > 32768)
161 v = roc - 1;
162 } else {
163 if (seq_largest - 32768 > seq)
164 v = roc + 1;
165 }
166 if (v == roc) {
167 seq_largest = FFMAX(seq_largest, seq);
168 } else if (v == roc + 1) {
169 seq_largest = seq;
170 roc = v;
171 }
172 index = seq + (((uint64_t)v) << 16);
173
174 AV_WB32(rocbuf, roc);
175 av_hmac_update(s->hmac, rocbuf, 4);
176 }
177
178 av_hmac_final(s->hmac, hmac, sizeof(hmac));
179 if (memcmp(hmac, buf + len - hmac_size, hmac_size)) {
180 av_log(NULL, AV_LOG_WARNING, "HMAC mismatch\n");
181 return AVERROR_INVALIDDATA;
182 }
183
184 len -= hmac_size;
185 *lenptr = len;
186
187 if (len < 12)
188 return AVERROR_INVALIDDATA;
189
190 if (rtcp) {
191 uint32_t srtcp_index = AV_RB32(buf + len - 4);
192 len -= 4;
193 *lenptr = len;
194
195 ssrc = AV_RB32(buf + 4);
196 index = srtcp_index & 0x7fffffff;
197
198 buf += 8;
199 len -= 8;
200 if (!(srtcp_index & 0x80000000))
201 return 0;
202 } else {
203 int ext, csrc;
204 s->seq_initialized = 1;
205 s->seq_largest = seq_largest;
206 s->roc = roc;
207
208 csrc = buf[0] & 0x0f;
209 ext = buf[0] & 0x10;
210 ssrc = AV_RB32(buf + 8);
211
212 buf += 12;
213 len -= 12;
214
215 buf += 4 * csrc;
216 len -= 4 * csrc;
217 if (len < 0)
218 return AVERROR_INVALIDDATA;
219
220 if (ext) {
221 if (len < 4)
222 return AVERROR_INVALIDDATA;
223 ext = (AV_RB16(buf + 2) + 1) * 4;
224 if (len < ext)
225 return AVERROR_INVALIDDATA;
226 len -= ext;
227 buf += ext;
228 }
229 }
230
231 create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc);
232 av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0);
233 encrypt_counter(s->aes, iv, buf, len);
234
235 return 0;
236 }
237
238 int ff_srtp_encrypt(struct SRTPContext *s, const uint8_t *in, int len,
239 uint8_t *out, int outlen)
240 {
241 uint8_t iv[16] = { 0 }, hmac[20];
242 uint64_t index;
243 uint32_t ssrc;
244 int rtcp, hmac_size, padding;
245 uint8_t *buf;
246
247 if (len < 8)
248 return AVERROR_INVALIDDATA;
249
250 rtcp = RTP_PT_IS_RTCP(in[1]);
251 hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size;
252 padding = hmac_size;
253 if (rtcp)
254 padding += 4; // For the RTCP index
255
256 if (len + padding > outlen)
257 return 0;
258
259 memcpy(out, in, len);
260 buf = out;
261
262 if (rtcp) {
263 ssrc = AV_RB32(buf + 4);
264 index = s->rtcp_index++;
265
266 buf += 8;
267 len -= 8;
268 } else {
269 int ext, csrc;
270 int seq = AV_RB16(buf + 2);
271
272 if (len < 12)
273 return AVERROR_INVALIDDATA;
274
275 ssrc = AV_RB32(buf + 8);
276
277 if (seq < s->seq_largest)
278 s->roc++;
279 s->seq_largest = seq;
280 index = seq + (((uint64_t)s->roc) << 16);
281
282 csrc = buf[0] & 0x0f;
283 ext = buf[0] & 0x10;
284
285 buf += 12;
286 len -= 12;
287
288 buf += 4 * csrc;
289 len -= 4 * csrc;
290 if (len < 0)
291 return AVERROR_INVALIDDATA;
292
293 if (ext) {
294 if (len < 4)
295 return AVERROR_INVALIDDATA;
296 ext = (AV_RB16(buf + 2) + 1) * 4;
297 if (len < ext)
298 return AVERROR_INVALIDDATA;
299 len -= ext;
300 buf += ext;
301 }
302 }
303
304 create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc);
305 av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0);
306 encrypt_counter(s->aes, iv, buf, len);
307
308 if (rtcp) {
309 AV_WB32(buf + len, 0x80000000 | index);
310 len += 4;
311 }
312
313 av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth));
314 av_hmac_update(s->hmac, out, buf + len - out);
315 if (!rtcp) {
316 uint8_t rocbuf[4];
317 AV_WB32(rocbuf, s->roc);
318 av_hmac_update(s->hmac, rocbuf, 4);
319 }
320 av_hmac_final(s->hmac, hmac, sizeof(hmac));
321
322 memcpy(buf + len, hmac, hmac_size);
323 len += hmac_size;
324 return buf + len - out;
325 }