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ffmpeg/libavformat/srtp.c

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/*
* 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;
}
#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 */
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