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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this file,
* You can obtain one at http://mozilla.org/MPL/2.0/. */
// Original author: ekr@rtfm.com
#include "transportlayersrtp.h"
#include "transportlayerdtls.h"
#include "logging.h"
#include "nsError.h"
#include "mozilla/Assertions.h"
namespace mozilla {
MOZ_MTLOG_MODULE("mtransport")
static char kDTLSExporterLabel[] = "EXTRACTOR-dtls_srtp";
TransportLayerSrtp::TransportLayerSrtp(TransportLayerDtls& dtls) {
// We need to connect to the dtls layer, not the ice layer, because even
// though the packets that DTLS decrypts don't flow through us, we do base our
// keying information on the keying information established by the DTLS layer.
dtls.SignalStateChange.connect(this, &TransportLayerSrtp::StateChange);
TL_SET_STATE(dtls.state());
}
void TransportLayerSrtp::WasInserted() {
// Connect to the lower layers
if (!Setup()) {
TL_SET_STATE(TS_ERROR);
}
}
bool TransportLayerSrtp::Setup() {
CheckThread();
if (!downward_) {
MOZ_MTLOG(ML_ERROR, "SRTP layer with nothing below. This is useless");
return false;
}
// downward_ is the TransportLayerIce
downward_->SignalPacketReceived.connect(this,
&TransportLayerSrtp::PacketReceived);
return true;
}
TransportResult TransportLayerSrtp::SendPacket(MediaPacket& packet) {
if (state() != TS_OPEN) {
return TE_ERROR;
}
if (packet.len() < 4) {
MOZ_ASSERT(false);
return TE_ERROR;
}
MOZ_ASSERT(packet.capacity() - packet.len() >= SRTP_MAX_EXPANSION);
int out_len;
nsresult res;
switch (packet.type()) {
case MediaPacket::RTP:
res = mSendSrtp->ProtectRtp(packet.data(), packet.len(),
packet.capacity(), &out_len);
packet.SetType(MediaPacket::SRTP);
break;
case MediaPacket::RTCP:
res = mSendSrtp->ProtectRtcp(packet.data(), packet.len(),
packet.capacity(), &out_len);
packet.SetType(MediaPacket::SRTCP);
break;
default:
MOZ_CRASH("SRTP layer asked to send packet that is neither RTP or RTCP");
}
if (NS_FAILED(res)) {
MOZ_MTLOG(ML_ERROR,
"Error protecting "
<< (packet.type() == MediaPacket::RTP ? "RTP" : "RTCP")
<< " len=" << packet.len() << "[" << std::hex
<< packet.data()[0] << " " << packet.data()[1] << " "
<< packet.data()[2] << " " << packet.data()[3] << "]");
return TE_ERROR;
}
size_t unencrypted_len = packet.len();
packet.SetLength(out_len);
TransportResult bytes = downward_->SendPacket(packet);
if (bytes == out_len) {
// Whole packet was written, but the encrypted length might be different.
// Don't confuse the caller.
return unencrypted_len;
}
if (bytes == TE_WOULDBLOCK) {
return TE_WOULDBLOCK;
}
return TE_ERROR;
}
void TransportLayerSrtp::StateChange(TransportLayer* layer, State state) {
if (state == TS_OPEN && !mSendSrtp) {
TransportLayerDtls* dtls = static_cast<TransportLayerDtls*>(layer);
MOZ_ASSERT(dtls); // DTLS is mandatory
uint16_t cipher_suite;
nsresult res = dtls->GetSrtpCipher(&cipher_suite);
if (NS_FAILED(res)) {
MOZ_MTLOG(ML_DEBUG, "DTLS-SRTP disabled");
TL_SET_STATE(TS_ERROR);
return;
}
unsigned int key_size = SrtpFlow::KeySize(cipher_suite);
unsigned int salt_size = SrtpFlow::SaltSize(cipher_suite);
unsigned int master_key_size = key_size + salt_size;
MOZ_ASSERT(master_key_size <= SRTP_MAX_KEY_LENGTH);
// SRTP Key Exporter as per RFC 5764 S 4.2
unsigned char srtp_block[SRTP_MAX_KEY_LENGTH * 2];
res = dtls->ExportKeyingMaterial(kDTLSExporterLabel, false, "", srtp_block,
sizeof(srtp_block));
if (NS_FAILED(res)) {
MOZ_MTLOG(ML_ERROR, "Failed to compute DTLS-SRTP keys. This is an error");
TL_SET_STATE(TS_ERROR);
return;
}
// Slice and dice as per RFC 5764 S 4.2
unsigned char client_write_key[SRTP_MAX_KEY_LENGTH];
unsigned char server_write_key[SRTP_MAX_KEY_LENGTH];
unsigned int offset = 0;
memcpy(client_write_key, srtp_block + offset, key_size);
offset += key_size;
memcpy(server_write_key, srtp_block + offset, key_size);
offset += key_size;
memcpy(client_write_key + key_size, srtp_block + offset, salt_size);
offset += salt_size;
memcpy(server_write_key + key_size, srtp_block + offset, salt_size);
MOZ_ASSERT((offset + salt_size) == (2 * master_key_size));
unsigned char* write_key;
unsigned char* read_key;
if (dtls->role() == TransportLayerDtls::CLIENT) {
write_key = client_write_key;
read_key = server_write_key;
} else {
write_key = server_write_key;
read_key = client_write_key;
}
MOZ_ASSERT(!mSendSrtp && !mRecvSrtp);
mSendSrtp =
SrtpFlow::Create(cipher_suite, false, write_key, master_key_size);
mRecvSrtp = SrtpFlow::Create(cipher_suite, true, read_key, master_key_size);
if (!mSendSrtp || !mRecvSrtp) {
MOZ_MTLOG(ML_ERROR, "Couldn't create SRTP flow.");
TL_SET_STATE(TS_ERROR);
return;
}
MOZ_MTLOG(ML_INFO, "Created SRTP flow!");
}
TL_SET_STATE(state);
}
void TransportLayerSrtp::PacketReceived(TransportLayer* layer,
MediaPacket& packet) {
if (state() != TS_OPEN) {
return;
}
if (!packet.data()) {
// Something ate this, probably the DTLS layer
return;
}
if (packet.type() != MediaPacket::SRTP &&
packet.type() != MediaPacket::SRTCP) {
return;
}
// We want to keep the encrypted packet around for packet dumping
packet.CopyDataToEncrypted();
int outLen;
nsresult res;
if (packet.type() == MediaPacket::SRTP) {
packet.SetType(MediaPacket::RTP);
res = mRecvSrtp->UnprotectRtp(packet.data(), packet.len(), packet.len(),
&outLen);
} else {
packet.SetType(MediaPacket::RTCP);
res = mRecvSrtp->UnprotectRtcp(packet.data(), packet.len(), packet.len(),
&outLen);
}
if (NS_SUCCEEDED(res)) {
packet.SetLength(outLen);
SignalPacketReceived(this, packet);
} else {
// TODO: What do we do wrt packet dumping here? Maybe signal an empty
// packet? Signal the still-encrypted packet?
MOZ_MTLOG(ML_ERROR,
"Error unprotecting "
<< (packet.type() == MediaPacket::RTP ? "RTP" : "RTCP")
<< " len=" << packet.len() << "[" << std::hex
<< packet.data()[0] << " " << packet.data()[1] << " "
<< packet.data()[2] << " " << packet.data()[3] << "]");
}
}
} // namespace mozilla
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