1/* 2 * SRTP encryption/decryption 3 * Copyright (c) 2012 Martin Storsjo 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 */ 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 31void 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 41static 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 54static 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 65int 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 112static 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 126int 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 238int 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 330static const char *aes128_80_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn"; 331 332static 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 341static 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 353static const char *aes128_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn"; 354 355static 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 364static 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 376static const char *aes128_80_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn"; 377 378static 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 387static 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 399static 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 407static 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 418static 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 439int 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 */ 473