| 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 | |
| 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 | } |
| 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 */ |