FFmpeg: libavformat/srtp.c Source File

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libavformat

srtp.c

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1 /*

2 * SRTP encryption/decryption

4 *

5 * This file is part of FFmpeg.

6 *

7 * FFmpeg 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 * FFmpeg 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 FFmpeg; if not, write to the Free Software

19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

20 */

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"

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 }

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 }

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 }

65 int ff_srtp_set_crypto(struct SRTPContext *s, const char *suite,

66 const char *params)

67 {

68 uint8_t buf[30];

70 ff_srtp_free(s);

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);

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 }

326

327 #ifdef TEST

328 #include <stdio.h>

329

330 static const char *aes128_80_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";

331

332 static const uint8_t rtp_aes128_80[] = {

333 // RTP header

334 0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,

335 // encrypted payload

336 0x62, 0x69, 0x76, 0xca, 0xc5,

337 // HMAC

338 0xa1, 0xac, 0x1b, 0xb4, 0xa0, 0x1c, 0xd5, 0x49, 0x28, 0x99,

339 };

340

341 static const uint8_t rtcp_aes128_80[] = {

342 // RTCP header

343 0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,

344 // encrypted payload

345 0x8a, 0xac, 0xdc, 0xa5, 0x4c, 0xf6, 0x78, 0xa6, 0x62, 0x8f, 0x24, 0xda,

346 0x6c, 0x09, 0x3f, 0xa9, 0x28, 0x7a, 0xb5, 0x7f, 0x1f, 0x0f, 0xc9, 0x35,

347 // RTCP index

348 0x80, 0x00, 0x00, 0x03,

349 // HMAC

350 0xe9, 0x3b, 0xc0, 0x5c, 0x0c, 0x06, 0x9f, 0xab, 0xc0, 0xde,

351 };

352

353 static const char *aes128_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";

354

355 static const uint8_t rtp_aes128_32[] = {

356 // RTP header

357 0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,

358 // encrypted payload

359 0x62, 0x69, 0x76, 0xca, 0xc5,

360 // HMAC

361 0xa1, 0xac, 0x1b, 0xb4,

362 };

363

364 static const uint8_t rtcp_aes128_32[] = {

365 // RTCP header

366 0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,

367 // encrypted payload

368 0x35, 0xe9, 0xb5, 0xff, 0x0d, 0xd1, 0xde, 0x70, 0x74, 0x10, 0xaa, 0x1b,

369 0xb2, 0x8d, 0xf0, 0x20, 0x02, 0x99, 0x6b, 0x1b, 0x0b, 0xd0, 0x47, 0x34,

370 // RTCP index

371 0x80, 0x00, 0x00, 0x04,

372 // HMAC

373 0x5b, 0xd2, 0xa9, 0x9d,

374 };

375

376 static const char *aes128_80_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn";

377

378 static const uint8_t rtp_aes128_80_32[] = {

379 // RTP header

380 0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78,

381 // encrypted payload

382 0x62, 0x69, 0x76, 0xca, 0xc5,

383 // HMAC

384 0xa1, 0xac, 0x1b, 0xb4,

385 };

386

387 static const uint8_t rtcp_aes128_80_32[] = {

388 // RTCP header

389 0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78,

390 // encrypted payload

391 0xd6, 0xae, 0xc1, 0x58, 0x63, 0x70, 0xc9, 0x88, 0x66, 0x26, 0x1c, 0x53,

392 0xff, 0x5d, 0x5d, 0x2b, 0x0f, 0x8c, 0x72, 0x3e, 0xc9, 0x1d, 0x43, 0xf9,

393 // RTCP index

394 0x80, 0x00, 0x00, 0x05,

395 // HMAC

396 0x09, 0x16, 0xb4, 0x27, 0x9a, 0xe9, 0x92, 0x26, 0x4e, 0x10,

397 };

398

399 static void print_data(const uint8_t *buf, int len)

400 {

401 int i;

402 for (i = 0; i < len; i++)

403 printf("%02x", buf[i]);

404 printf("\n");

405 }

406

407 static int test_decrypt(struct SRTPContext *srtp, const uint8_t *in, int len,

408 uint8_t *out)

409 {

410 memcpy(out, in, len);

411 if (!ff_srtp_decrypt(srtp, out, &len)) {

412 print_data(out, len);

413 return len;

414 } else

415 return -1;

416 }

417

418 static void test_encrypt(const uint8_t *data, int in_len, const char *suite,

419 const char *key)

420 {

421 struct SRTPContext enc = { 0 }, dec = { 0 };

422 int len;

423 char buf[RTP_MAX_PACKET_LENGTH];

424 ff_srtp_set_crypto(&enc, suite, key);

425 ff_srtp_set_crypto(&dec, suite, key);

426 len = ff_srtp_encrypt(&enc, data, in_len, buf, sizeof(buf));

427 if (!ff_srtp_decrypt(&dec, buf, &len)) {

428 if (len == in_len && !memcmp(buf, data, len))

429 printf("Decrypted content matches input\n");

430 else

431 printf("Decrypted content doesn't match input\n");

432 } else {

433 printf("Decryption failed\n");

434 }

435 ff_srtp_free(&enc);

436 ff_srtp_free(&dec);

437 }

438

439 int main(void)

440 {

441 static const char *aes128_80_suite = "AES_CM_128_HMAC_SHA1_80";

442 static const char *aes128_32_suite = "AES_CM_128_HMAC_SHA1_32";

443 static const char *aes128_80_32_suite = "SRTP_AES128_CM_HMAC_SHA1_32";

444 static const char *test_key = "abcdefghijklmnopqrstuvwxyz1234567890ABCD";

445 uint8_t buf[RTP_MAX_PACKET_LENGTH];

446 struct SRTPContext srtp = { 0 };

447 int len;

448 ff_srtp_set_crypto(&srtp, aes128_80_suite, aes128_80_key);

449 len = test_decrypt(&srtp, rtp_aes128_80, sizeof(rtp_aes128_80), buf);

450 test_encrypt(buf, len, aes128_80_suite, test_key);

451 test_encrypt(buf, len, aes128_32_suite, test_key);

452 test_encrypt(buf, len, aes128_80_32_suite, test_key);

453 test_decrypt(&srtp, rtcp_aes128_80, sizeof(rtcp_aes128_80), buf);

454 test_encrypt(buf, len, aes128_80_suite, test_key);

455 test_encrypt(buf, len, aes128_32_suite, test_key);

456 test_encrypt(buf, len, aes128_80_32_suite, test_key);

457 ff_srtp_free(&srtp);

458

459 memset(&srtp, 0, sizeof(srtp)); // Clear the context

460 ff_srtp_set_crypto(&srtp, aes128_32_suite, aes128_32_key);

461 test_decrypt(&srtp, rtp_aes128_32, sizeof(rtp_aes128_32), buf);

462 test_decrypt(&srtp, rtcp_aes128_32, sizeof(rtcp_aes128_32), buf);

463 ff_srtp_free(&srtp);

464

465 memset(&srtp, 0, sizeof(srtp)); // Clear the context

466 ff_srtp_set_crypto(&srtp, aes128_80_32_suite, aes128_80_32_key);

467 test_decrypt(&srtp, rtp_aes128_80_32, sizeof(rtp_aes128_80_32), buf);

468 test_decrypt(&srtp, rtcp_aes128_80_32, sizeof(rtcp_aes128_80_32), buf);

469 ff_srtp_free(&srtp);

470 return 0;

471 }

472 #endif /* TEST */

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