/* * SRTP encryption/decryption * Copyright (c) 2012 Martin Storsjo * * This file is part of Libav. * * Libav 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. * * Libav 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 Libav; 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; } #ifdef TEST #include <stdio.h> static const char *aes128_80_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn"; static const uint8_t rtp_aes128_80[] = { // RTP header 0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78, // encrypted payload 0x62, 0x69, 0x76, 0xca, 0xc5, // HMAC 0xa1, 0xac, 0x1b, 0xb4, 0xa0, 0x1c, 0xd5, 0x49, 0x28, 0x99, }; static const uint8_t rtcp_aes128_80[] = { // RTCP header 0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78, // encrypted payload 0x8a, 0xac, 0xdc, 0xa5, 0x4c, 0xf6, 0x78, 0xa6, 0x62, 0x8f, 0x24, 0xda, 0x6c, 0x09, 0x3f, 0xa9, 0x28, 0x7a, 0xb5, 0x7f, 0x1f, 0x0f, 0xc9, 0x35, // RTCP index 0x80, 0x00, 0x00, 0x03, // HMAC 0xe9, 0x3b, 0xc0, 0x5c, 0x0c, 0x06, 0x9f, 0xab, 0xc0, 0xde, }; static const char *aes128_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn"; static const uint8_t rtp_aes128_32[] = { // RTP header 0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78, // encrypted payload 0x62, 0x69, 0x76, 0xca, 0xc5, // HMAC 0xa1, 0xac, 0x1b, 0xb4, }; static const uint8_t rtcp_aes128_32[] = { // RTCP header 0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78, // encrypted payload 0x35, 0xe9, 0xb5, 0xff, 0x0d, 0xd1, 0xde, 0x70, 0x74, 0x10, 0xaa, 0x1b, 0xb2, 0x8d, 0xf0, 0x20, 0x02, 0x99, 0x6b, 0x1b, 0x0b, 0xd0, 0x47, 0x34, // RTCP index 0x80, 0x00, 0x00, 0x04, // HMAC 0x5b, 0xd2, 0xa9, 0x9d, }; static const char *aes128_80_32_key = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn"; static const uint8_t rtp_aes128_80_32[] = { // RTP header 0x80, 0xe0, 0x12, 0x34, 0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78, // encrypted payload 0x62, 0x69, 0x76, 0xca, 0xc5, // HMAC 0xa1, 0xac, 0x1b, 0xb4, }; static const uint8_t rtcp_aes128_80_32[] = { // RTCP header 0x81, 0xc9, 0x00, 0x07, 0x12, 0x34, 0x56, 0x78, // encrypted payload 0xd6, 0xae, 0xc1, 0x58, 0x63, 0x70, 0xc9, 0x88, 0x66, 0x26, 0x1c, 0x53, 0xff, 0x5d, 0x5d, 0x2b, 0x0f, 0x8c, 0x72, 0x3e, 0xc9, 0x1d, 0x43, 0xf9, // RTCP index 0x80, 0x00, 0x00, 0x05, // HMAC 0x09, 0x16, 0xb4, 0x27, 0x9a, 0xe9, 0x92, 0x26, 0x4e, 0x10, }; static void print_data(const uint8_t *buf, int len) { int i; for (i = 0; i < len; i++) printf("%02x", buf[i]); printf("\n"); } static int test_decrypt(struct SRTPContext *srtp, const uint8_t *in, int len, uint8_t *out) { memcpy(out, in, len); if (!ff_srtp_decrypt(srtp, out, &len)) { print_data(out, len); return len; } else return -1; } static void test_encrypt(const uint8_t *data, int in_len, const char *suite, const char *key) { struct SRTPContext enc = { 0 }, dec = { 0 }; int len; char buf[RTP_MAX_PACKET_LENGTH]; ff_srtp_set_crypto(&enc, suite, key); ff_srtp_set_crypto(&dec, suite, key); len = ff_srtp_encrypt(&enc, data, in_len, buf, sizeof(buf)); if (!ff_srtp_decrypt(&dec, buf, &len)) { if (len == in_len && !memcmp(buf, data, len)) printf("Decrypted content matches input\n"); else printf("Decrypted content doesn't match input\n"); } else { printf("Decryption failed\n"); } ff_srtp_free(&enc); ff_srtp_free(&dec); } int main(void) { static const char *aes128_80_suite = "AES_CM_128_HMAC_SHA1_80"; static const char *aes128_32_suite = "AES_CM_128_HMAC_SHA1_32"; static const char *aes128_80_32_suite = "SRTP_AES128_CM_HMAC_SHA1_32"; static const char *test_key = "abcdefghijklmnopqrstuvwxyz1234567890ABCD"; uint8_t buf[RTP_MAX_PACKET_LENGTH]; struct SRTPContext srtp = { 0 }; int len; ff_srtp_set_crypto(&srtp, aes128_80_suite, aes128_80_key); len = test_decrypt(&srtp, rtp_aes128_80, sizeof(rtp_aes128_80), buf); test_encrypt(buf, len, aes128_80_suite, test_key); test_encrypt(buf, len, aes128_32_suite, test_key); test_encrypt(buf, len, aes128_80_32_suite, test_key); test_decrypt(&srtp, rtcp_aes128_80, sizeof(rtcp_aes128_80), buf); test_encrypt(buf, len, aes128_80_suite, test_key); test_encrypt(buf, len, aes128_32_suite, test_key); test_encrypt(buf, len, aes128_80_32_suite, test_key); ff_srtp_free(&srtp); memset(&srtp, 0, sizeof(srtp)); // Clear the context ff_srtp_set_crypto(&srtp, aes128_32_suite, aes128_32_key); test_decrypt(&srtp, rtp_aes128_32, sizeof(rtp_aes128_32), buf); test_decrypt(&srtp, rtcp_aes128_32, sizeof(rtcp_aes128_32), buf); ff_srtp_free(&srtp); memset(&srtp, 0, sizeof(srtp)); // Clear the context ff_srtp_set_crypto(&srtp, aes128_80_32_suite, aes128_80_32_key); test_decrypt(&srtp, rtp_aes128_80_32, sizeof(rtp_aes128_80_32), buf); test_decrypt(&srtp, rtcp_aes128_80_32, sizeof(rtcp_aes128_80_32), buf); ff_srtp_free(&srtp); return 0; } #endif /* TEST */