| /* |
| * SRTP encryption/decryption |
| * Copyright (c) 2012 Martin Storsjo |
| * |
| * This file is part of FFmpeg. |
| * |
| * FFmpeg is free software; you can redistribute it and/or |
| * modify it under the terms of the GNU Lesser General Public |
| * License as published by the Free Software Foundation; either |
| * version 2.1 of the License, or (at your option) any later version. |
| * |
| * FFmpeg is distributed in the hope that it will be useful, |
| * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| * Lesser General Public License for more details. |
| * |
| * You should have received a copy of the GNU Lesser General Public |
| * License along with FFmpeg; if not, write to the Free Software |
| * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| */ |
| |
| #include "libavutil/base64.h" |
| #include "libavutil/aes.h" |
| #include "libavutil/hmac.h" |
| #include "libavutil/intreadwrite.h" |
| #include "libavutil/log.h" |
| #include "rtp.h" |
| #include "rtpdec.h" |
| #include "srtp.h" |
| |
| void ff_srtp_free(struct SRTPContext *s) |
| { |
| if (!s) |
| return; |
| av_freep(&s->aes); |
| if (s->hmac) |
| av_hmac_free(s->hmac); |
| s->hmac = NULL; |
| } |
| |
| static void encrypt_counter(struct AVAES *aes, uint8_t *iv, uint8_t *outbuf, |
| int outlen) |
| { |
| int i, j, outpos; |
| for (i = 0, outpos = 0; outpos < outlen; i++) { |
| uint8_t keystream[16]; |
| AV_WB16(&iv[14], i); |
| av_aes_crypt(aes, keystream, iv, 1, NULL, 0); |
| for (j = 0; j < 16 && outpos < outlen; j++, outpos++) |
| outbuf[outpos] ^= keystream[j]; |
| } |
| } |
| |
| static void derive_key(struct AVAES *aes, const uint8_t *salt, int label, |
| uint8_t *out, int outlen) |
| { |
| uint8_t input[16] = { 0 }; |
| memcpy(input, salt, 14); |
| // Key derivation rate assumed to be zero |
| input[14 - 7] ^= label; |
| memset(out, 0, outlen); |
| encrypt_counter(aes, input, out, outlen); |
| } |
| |
| int ff_srtp_set_crypto(struct SRTPContext *s, const char *suite, |
| const char *params) |
| { |
| uint8_t buf[30]; |
| |
| ff_srtp_free(s); |
| |
| // RFC 4568 |
| if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_80") || |
| !strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_80")) { |
| s->rtp_hmac_size = s->rtcp_hmac_size = 10; |
| } else if (!strcmp(suite, "AES_CM_128_HMAC_SHA1_32")) { |
| s->rtp_hmac_size = s->rtcp_hmac_size = 4; |
| } else if (!strcmp(suite, "SRTP_AES128_CM_HMAC_SHA1_32")) { |
| // RFC 5764 section 4.1.2 |
| s->rtp_hmac_size = 4; |
| s->rtcp_hmac_size = 10; |
| } else { |
| av_log(NULL, AV_LOG_WARNING, "SRTP Crypto suite %s not supported\n", |
| suite); |
| return AVERROR(EINVAL); |
| } |
| if (av_base64_decode(buf, params, sizeof(buf)) != sizeof(buf)) { |
| av_log(NULL, AV_LOG_WARNING, "Incorrect amount of SRTP params\n"); |
| return AVERROR(EINVAL); |
| } |
| // MKI and lifetime not handled yet |
| s->aes = av_aes_alloc(); |
| s->hmac = av_hmac_alloc(AV_HMAC_SHA1); |
| if (!s->aes || !s->hmac) |
| return AVERROR(ENOMEM); |
| memcpy(s->master_key, buf, 16); |
| memcpy(s->master_salt, buf + 16, 14); |
| |
| // RFC 3711 |
| av_aes_init(s->aes, s->master_key, 128, 0); |
| |
| derive_key(s->aes, s->master_salt, 0x00, s->rtp_key, sizeof(s->rtp_key)); |
| derive_key(s->aes, s->master_salt, 0x02, s->rtp_salt, sizeof(s->rtp_salt)); |
| derive_key(s->aes, s->master_salt, 0x01, s->rtp_auth, sizeof(s->rtp_auth)); |
| |
| derive_key(s->aes, s->master_salt, 0x03, s->rtcp_key, sizeof(s->rtcp_key)); |
| derive_key(s->aes, s->master_salt, 0x05, s->rtcp_salt, sizeof(s->rtcp_salt)); |
| derive_key(s->aes, s->master_salt, 0x04, s->rtcp_auth, sizeof(s->rtcp_auth)); |
| return 0; |
| } |
| |
| static void create_iv(uint8_t *iv, const uint8_t *salt, uint64_t index, |
| uint32_t ssrc) |
| { |
| uint8_t indexbuf[8]; |
| int i; |
| memset(iv, 0, 16); |
| AV_WB32(&iv[4], ssrc); |
| AV_WB64(indexbuf, index); |
| for (i = 0; i < 8; i++) // index << 16 |
| iv[6 + i] ^= indexbuf[i]; |
| for (i = 0; i < 14; i++) |
| iv[i] ^= salt[i]; |
| } |
| |
| int ff_srtp_decrypt(struct SRTPContext *s, uint8_t *buf, int *lenptr) |
| { |
| uint8_t iv[16] = { 0 }, hmac[20]; |
| int len = *lenptr; |
| int av_uninit(seq_largest); |
| uint32_t ssrc, av_uninit(roc); |
| uint64_t index; |
| int rtcp, hmac_size; |
| |
| // TODO: Missing replay protection |
| |
| if (len < 2) |
| return AVERROR_INVALIDDATA; |
| |
| rtcp = RTP_PT_IS_RTCP(buf[1]); |
| hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size; |
| |
| if (len < hmac_size) |
| return AVERROR_INVALIDDATA; |
| |
| // Authentication HMAC |
| av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth)); |
| // If MKI is used, this should exclude the MKI as well |
| av_hmac_update(s->hmac, buf, len - hmac_size); |
| |
| if (!rtcp) { |
| int seq = AV_RB16(buf + 2); |
| uint32_t v; |
| uint8_t rocbuf[4]; |
| |
| // RFC 3711 section 3.3.1, appendix A |
| seq_largest = s->seq_initialized ? s->seq_largest : seq; |
| v = roc = s->roc; |
| if (seq_largest < 32768) { |
| if (seq - seq_largest > 32768) |
| v = roc - 1; |
| } else { |
| if (seq_largest - 32768 > seq) |
| v = roc + 1; |
| } |
| if (v == roc) { |
| seq_largest = FFMAX(seq_largest, seq); |
| } else if (v == roc + 1) { |
| seq_largest = seq; |
| roc = v; |
| } |
| index = seq + (((uint64_t)v) << 16); |
| |
| AV_WB32(rocbuf, roc); |
| av_hmac_update(s->hmac, rocbuf, 4); |
| } |
| |
| av_hmac_final(s->hmac, hmac, sizeof(hmac)); |
| if (memcmp(hmac, buf + len - hmac_size, hmac_size)) { |
| av_log(NULL, AV_LOG_WARNING, "HMAC mismatch\n"); |
| return AVERROR_INVALIDDATA; |
| } |
| |
| len -= hmac_size; |
| *lenptr = len; |
| |
| if (len < 12) |
| return AVERROR_INVALIDDATA; |
| |
| if (rtcp) { |
| uint32_t srtcp_index = AV_RB32(buf + len - 4); |
| len -= 4; |
| *lenptr = len; |
| |
| ssrc = AV_RB32(buf + 4); |
| index = srtcp_index & 0x7fffffff; |
| |
| buf += 8; |
| len -= 8; |
| if (!(srtcp_index & 0x80000000)) |
| return 0; |
| } else { |
| int ext, csrc; |
| s->seq_initialized = 1; |
| s->seq_largest = seq_largest; |
| s->roc = roc; |
| |
| csrc = buf[0] & 0x0f; |
| ext = buf[0] & 0x10; |
| ssrc = AV_RB32(buf + 8); |
| |
| buf += 12; |
| len -= 12; |
| |
| buf += 4 * csrc; |
| len -= 4 * csrc; |
| if (len < 0) |
| return AVERROR_INVALIDDATA; |
| |
| if (ext) { |
| if (len < 4) |
| return AVERROR_INVALIDDATA; |
| ext = (AV_RB16(buf + 2) + 1) * 4; |
| if (len < ext) |
| return AVERROR_INVALIDDATA; |
| len -= ext; |
| buf += ext; |
| } |
| } |
| |
| create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc); |
| av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0); |
| encrypt_counter(s->aes, iv, buf, len); |
| |
| return 0; |
| } |
| |
| int ff_srtp_encrypt(struct SRTPContext *s, const uint8_t *in, int len, |
| uint8_t *out, int outlen) |
| { |
| uint8_t iv[16] = { 0 }, hmac[20]; |
| uint64_t index; |
| uint32_t ssrc; |
| int rtcp, hmac_size, padding; |
| uint8_t *buf; |
| |
| if (len < 8) |
| return AVERROR_INVALIDDATA; |
| |
| rtcp = RTP_PT_IS_RTCP(in[1]); |
| hmac_size = rtcp ? s->rtcp_hmac_size : s->rtp_hmac_size; |
| padding = hmac_size; |
| if (rtcp) |
| padding += 4; // For the RTCP index |
| |
| if (len + padding > outlen) |
| return 0; |
| |
| memcpy(out, in, len); |
| buf = out; |
| |
| if (rtcp) { |
| ssrc = AV_RB32(buf + 4); |
| index = s->rtcp_index++; |
| |
| buf += 8; |
| len -= 8; |
| } else { |
| int ext, csrc; |
| int seq = AV_RB16(buf + 2); |
| |
| if (len < 12) |
| return AVERROR_INVALIDDATA; |
| |
| ssrc = AV_RB32(buf + 8); |
| |
| if (seq < s->seq_largest) |
| s->roc++; |
| s->seq_largest = seq; |
| index = seq + (((uint64_t)s->roc) << 16); |
| |
| csrc = buf[0] & 0x0f; |
| ext = buf[0] & 0x10; |
| |
| buf += 12; |
| len -= 12; |
| |
| buf += 4 * csrc; |
| len -= 4 * csrc; |
| if (len < 0) |
| return AVERROR_INVALIDDATA; |
| |
| if (ext) { |
| if (len < 4) |
| return AVERROR_INVALIDDATA; |
| ext = (AV_RB16(buf + 2) + 1) * 4; |
| if (len < ext) |
| return AVERROR_INVALIDDATA; |
| len -= ext; |
| buf += ext; |
| } |
| } |
| |
| create_iv(iv, rtcp ? s->rtcp_salt : s->rtp_salt, index, ssrc); |
| av_aes_init(s->aes, rtcp ? s->rtcp_key : s->rtp_key, 128, 0); |
| encrypt_counter(s->aes, iv, buf, len); |
| |
| if (rtcp) { |
| AV_WB32(buf + len, 0x80000000 | index); |
| len += 4; |
| } |
| |
| av_hmac_init(s->hmac, rtcp ? s->rtcp_auth : s->rtp_auth, sizeof(s->rtp_auth)); |
| av_hmac_update(s->hmac, out, buf + len - out); |
| if (!rtcp) { |
| uint8_t rocbuf[4]; |
| AV_WB32(rocbuf, s->roc); |
| av_hmac_update(s->hmac, rocbuf, 4); |
| } |
| av_hmac_final(s->hmac, hmac, sizeof(hmac)); |
| |
| memcpy(buf + len, hmac, hmac_size); |
| len += hmac_size; |
| return buf + len - out; |
| } |