diff --git a/webrtc/p2p/base/fakepackettransport.h b/webrtc/p2p/base/fakepackettransport.h
index 16af9a42ae..82d39c2364 100644
--- a/webrtc/p2p/base/fakepackettransport.h
+++ b/webrtc/p2p/base/fakepackettransport.h
@@ -86,6 +86,8 @@ class FakePacketTransport : public PacketTransportInternal {
   bool GetOption(Socket::Option opt, int* value) override { return true; }
   int GetError() override { return 0; }
 
+  const CopyOnWriteBuffer* last_sent_packet() { return &last_sent_packet_; }
+
  private:
   void set_writable(bool writable) {
     if (writable_ == writable) {
@@ -107,12 +109,14 @@ class FakePacketTransport : public PacketTransportInternal {
   }
 
   void SendPacketInternal(const CopyOnWriteBuffer& packet) {
+    last_sent_packet_ = packet;
     if (dest_) {
       dest_->SignalReadPacket(dest_, packet.data<char>(), packet.size(),
                               CreatePacketTime(0), 0);
     }
   }
 
+  CopyOnWriteBuffer last_sent_packet_;
   AsyncInvoker invoker_;
   std::string debug_name_;
   FakePacketTransport* dest_ = nullptr;
diff --git a/webrtc/pc/channel.cc b/webrtc/pc/channel.cc
index 59f0869431..d99a105868 100644
--- a/webrtc/pc/channel.cc
+++ b/webrtc/pc/channel.cc
@@ -158,18 +158,22 @@ BaseChannel::BaseChannel(rtc::Thread* worker_thread,
       signaling_thread_(signaling_thread),
       content_name_(content_name),
       rtcp_mux_required_(rtcp_mux_required),
-      rtp_transport_(
-          srtp_required
-              ? rtc::WrapUnique<webrtc::RtpTransportInternal>(
-                    new webrtc::SrtpTransport(rtcp_mux_required, content_name))
-              : rtc::MakeUnique<webrtc::RtpTransport>(rtcp_mux_required)),
       srtp_required_(srtp_required),
       media_channel_(media_channel),
       selected_candidate_pair_(nullptr) {
   RTC_DCHECK(worker_thread_ == rtc::Thread::Current());
+  if (srtp_required) {
+    auto transport =
+        rtc::MakeUnique<webrtc::SrtpTransport>(rtcp_mux_required, content_name);
+    srtp_transport_ = transport.get();
+    rtp_transport_ = std::move(transport);
 #if defined(ENABLE_EXTERNAL_AUTH)
-  srtp_filter_.EnableExternalAuth();
+    srtp_transport_->EnableExternalAuth();
 #endif
+  } else {
+    rtp_transport_ = rtc::MakeUnique<webrtc::RtpTransport>(rtcp_mux_required);
+    srtp_transport_ = nullptr;
+  }
   rtp_transport_->SignalReadyToSend.connect(
       this, &BaseChannel::OnTransportReadyToSend);
   // TODO(zstein):  RtpTransport::SignalPacketReceived will probably be replaced
@@ -314,14 +318,17 @@ void BaseChannel::SetTransports_n(
     return;
   }
 
-  // When using DTLS-SRTP, we must reset the SrtpFilter every time the transport
-  // changes and wait until the DTLS handshake is complete to set the newly
-  // negotiated parameters.
+  // When using DTLS-SRTP, we must reset the SrtpTransport every time the
+  // DtlsTransport changes and wait until the DTLS handshake is complete to set
+  // the newly negotiated parameters.
   if (ShouldSetupDtlsSrtp_n()) {
     // Set |writable_| to false such that UpdateWritableState_w can set up
     // DTLS-SRTP when |writable_| becomes true again.
     writable_ = false;
-    srtp_filter_.ResetParams();
+    dtls_active_ = false;
+    if (srtp_transport_) {
+      srtp_transport_->ResetParams();
+    }
   }
 
   // If this BaseChannel doesn't require RTCP mux and we haven't fully
@@ -377,8 +384,8 @@ void BaseChannel::SetTransport_n(
   }
 
   if (rtcp && new_dtls_transport) {
-    RTC_CHECK(!(ShouldSetupDtlsSrtp_n() && srtp_filter_.IsActive()))
-        << "Setting RTCP for DTLS/SRTP after SrtpFilter is active "
+    RTC_CHECK(!(ShouldSetupDtlsSrtp_n() && srtp_active()))
+        << "Setting RTCP for DTLS/SRTP after the DTLS is active "
         << "should never happen.";
   }
 
@@ -529,8 +536,7 @@ bool BaseChannel::IsReadyToSendMedia_n() const {
   // and we have had some form of connectivity.
   return enabled() && IsReceiveContentDirection(remote_content_direction_) &&
          IsSendContentDirection(local_content_direction_) &&
-         was_ever_writable() &&
-         (srtp_filter_.IsActive() || !ShouldSetupDtlsSrtp_n());
+         was_ever_writable() && (srtp_active() || !ShouldSetupDtlsSrtp_n());
 }
 
 bool BaseChannel::SendPacket(rtc::CopyOnWriteBuffer* packet,
@@ -582,13 +588,16 @@ void BaseChannel::OnDtlsState(DtlsTransportInternal* transport,
     return;
   }
 
-  // Reset the srtp filter if it's not the CONNECTED state. For the CONNECTED
+  // Reset the SrtpTransport if it's not the CONNECTED state. For the CONNECTED
   // state, setting up DTLS-SRTP context is deferred to ChannelWritable_w to
   // cover other scenarios like the whole transport is writable (not just this
   // TransportChannel) or when TransportChannel is attached after DTLS is
   // negotiated.
   if (state != DTLS_TRANSPORT_CONNECTED) {
-    srtp_filter_.ResetParams();
+    dtls_active_ = false;
+    if (srtp_transport_) {
+      srtp_transport_->ResetParams();
+    }
   }
 }
 
@@ -662,91 +671,30 @@ bool BaseChannel::SendPacket(bool rtcp,
     return false;
   }
 
-  rtc::PacketOptions updated_options;
-  updated_options = options;
-  // Protect if needed.
-  if (srtp_filter_.IsActive()) {
-    TRACE_EVENT0("webrtc", "SRTP Encode");
-    bool res;
-    uint8_t* data = packet->data();
-    int len = static_cast<int>(packet->size());
-    if (!rtcp) {
-    // If ENABLE_EXTERNAL_AUTH flag is on then packet authentication is not done
-    // inside libsrtp for a RTP packet. A external HMAC module will be writing
-    // a fake HMAC value. This is ONLY done for a RTP packet.
-    // Socket layer will update rtp sendtime extension header if present in
-    // packet with current time before updating the HMAC.
-#if !defined(ENABLE_EXTERNAL_AUTH)
-      res = srtp_filter_.ProtectRtp(
-          data, len, static_cast<int>(packet->capacity()), &len);
-#else
-      if (!srtp_filter_.IsExternalAuthActive()) {
-        res = srtp_filter_.ProtectRtp(
-            data, len, static_cast<int>(packet->capacity()), &len);
-      } else {
-        updated_options.packet_time_params.rtp_sendtime_extension_id =
-            rtp_abs_sendtime_extn_id_;
-        res = srtp_filter_.ProtectRtp(
-            data, len, static_cast<int>(packet->capacity()), &len,
-            &updated_options.packet_time_params.srtp_packet_index);
-        // If protection succeeds, let's get auth params from srtp.
-        if (res) {
-          uint8_t* auth_key = NULL;
-          int key_len;
-          res = srtp_filter_.GetRtpAuthParams(
-              &auth_key, &key_len,
-              &updated_options.packet_time_params.srtp_auth_tag_len);
-          if (res) {
-            updated_options.packet_time_params.srtp_auth_key.resize(key_len);
-            updated_options.packet_time_params.srtp_auth_key.assign(
-                auth_key, auth_key + key_len);
-          }
-        }
-      }
-#endif
-      if (!res) {
-        int seq_num = -1;
-        uint32_t ssrc = 0;
-        GetRtpSeqNum(data, len, &seq_num);
-        GetRtpSsrc(data, len, &ssrc);
-        LOG(LS_ERROR) << "Failed to protect " << content_name_
-                      << " RTP packet: size=" << len
-                      << ", seqnum=" << seq_num << ", SSRC=" << ssrc;
+  if (!srtp_active()) {
+    if (srtp_required_) {
+      // The audio/video engines may attempt to send RTCP packets as soon as the
+      // streams are created, so don't treat this as an error for RTCP.
+      // See: https://bugs.chromium.org/p/webrtc/issues/detail?id=6809
+      if (rtcp) {
         return false;
       }
-    } else {
-      res = srtp_filter_.ProtectRtcp(data, len,
-                                     static_cast<int>(packet->capacity()),
-                                     &len);
-      if (!res) {
-        int type = -1;
-        GetRtcpType(data, len, &type);
-        LOG(LS_ERROR) << "Failed to protect " << content_name_
-                      << " RTCP packet: size=" << len << ", type=" << type;
-        return false;
-      }
-    }
-
-    // Update the length of the packet now that we've added the auth tag.
-    packet->SetSize(len);
-  } else if (srtp_required_) {
-    // The audio/video engines may attempt to send RTCP packets as soon as the
-    // streams are created, so don't treat this as an error for RTCP.
-    // See: https://bugs.chromium.org/p/webrtc/issues/detail?id=6809
-    if (rtcp) {
+      // However, there shouldn't be any RTP packets sent before SRTP is set up
+      // (and SetSend(true) is called).
+      LOG(LS_ERROR) << "Can't send outgoing RTP packet when SRTP is inactive"
+                    << " and crypto is required";
+      RTC_NOTREACHED();
       return false;
     }
-    // However, there shouldn't be any RTP packets sent before SRTP is set up
-    // (and SetSend(true) is called).
-    LOG(LS_ERROR) << "Can't send outgoing RTP packet when SRTP is inactive"
-                  << " and crypto is required";
-    RTC_NOTREACHED();
-    return false;
+    // Bon voyage.
+    return rtcp ? rtp_transport_->SendRtcpPacket(packet, options, PF_NORMAL)
+                : rtp_transport_->SendRtpPacket(packet, options, PF_NORMAL);
   }
-
+  RTC_DCHECK(srtp_transport_);
+  RTC_DCHECK(srtp_transport_->IsActive());
   // Bon voyage.
-  int flags = (secure() && secure_dtls()) ? PF_SRTP_BYPASS : PF_NORMAL;
-  return rtp_transport_->SendPacket(rtcp, packet, updated_options, flags);
+  return rtcp ? srtp_transport_->SendRtcpPacket(packet, options, PF_SRTP_BYPASS)
+              : srtp_transport_->SendRtpPacket(packet, options, PF_SRTP_BYPASS);
 }
 
 bool BaseChannel::HandlesPayloadType(int packet_type) const {
@@ -761,37 +709,7 @@ void BaseChannel::OnPacketReceived(bool rtcp,
     signaling_thread()->Post(RTC_FROM_HERE, this, MSG_FIRSTPACKETRECEIVED);
   }
 
-  // Unprotect the packet, if needed.
-  if (srtp_filter_.IsActive()) {
-    TRACE_EVENT0("webrtc", "SRTP Decode");
-    char* data = packet->data<char>();
-    int len = static_cast<int>(packet->size());
-    bool res;
-    if (!rtcp) {
-      res = srtp_filter_.UnprotectRtp(data, len, &len);
-      if (!res) {
-        int seq_num = -1;
-        uint32_t ssrc = 0;
-        GetRtpSeqNum(data, len, &seq_num);
-        GetRtpSsrc(data, len, &ssrc);
-        LOG(LS_ERROR) << "Failed to unprotect " << content_name_
-                      << " RTP packet: size=" << len << ", seqnum=" << seq_num
-                      << ", SSRC=" << ssrc;
-        return;
-      }
-    } else {
-      res = srtp_filter_.UnprotectRtcp(data, len, &len);
-      if (!res) {
-        int type = -1;
-        GetRtcpType(data, len, &type);
-        LOG(LS_ERROR) << "Failed to unprotect " << content_name_
-                      << " RTCP packet: size=" << len << ", type=" << type;
-        return;
-      }
-    }
-
-    packet->SetSize(len);
-  } else if (srtp_required_) {
+  if (!srtp_active() && srtp_required_) {
     // Our session description indicates that SRTP is required, but we got a
     // packet before our SRTP filter is active. This means either that
     // a) we got SRTP packets before we received the SDES keys, in which case
@@ -995,43 +913,37 @@ bool BaseChannel::SetupDtlsSrtp_n(bool rtcp) {
     recv_key = &server_write_key;
   }
 
-  if (!srtp_filter_.IsActive()) {
-    if (rtcp) {
-      ret = srtp_filter_.SetRtcpParams(selected_crypto_suite, &(*send_key)[0],
-                                       static_cast<int>(send_key->size()),
-                                       selected_crypto_suite, &(*recv_key)[0],
-                                       static_cast<int>(recv_key->size()));
+  if (rtcp) {
+    if (!dtls_active()) {
+      RTC_DCHECK(srtp_transport_);
+      ret = srtp_transport_->SetRtcpParams(
+          selected_crypto_suite, &(*send_key)[0],
+          static_cast<int>(send_key->size()), selected_crypto_suite,
+          &(*recv_key)[0], static_cast<int>(recv_key->size()));
     } else {
-      ret = srtp_filter_.SetRtpParams(selected_crypto_suite, &(*send_key)[0],
-                                      static_cast<int>(send_key->size()),
-                                      selected_crypto_suite, &(*recv_key)[0],
-                                      static_cast<int>(recv_key->size()));
+      // RTCP doesn't need to call SetRtpParam because it is only used
+      // to make the updated encrypted RTP header extension IDs take effect.
+      ret = true;
     }
   } else {
-    if (rtcp) {
-      // RTCP doesn't need to be updated because UpdateRtpParams is only used
-      // to update the set of encrypted RTP header extension IDs.
-      ret = true;
-    } else {
-      ret = srtp_filter_.UpdateRtpParams(
-          selected_crypto_suite,
-          &(*send_key)[0], static_cast<int>(send_key->size()),
-          selected_crypto_suite,
-          &(*recv_key)[0], static_cast<int>(recv_key->size()));
-    }
+    RTC_DCHECK(srtp_transport_);
+    ret = srtp_transport_->SetRtpParams(selected_crypto_suite, &(*send_key)[0],
+                                        static_cast<int>(send_key->size()),
+                                        selected_crypto_suite, &(*recv_key)[0],
+                                        static_cast<int>(recv_key->size()));
+    dtls_active_ = ret;
   }
 
   if (!ret) {
     LOG(LS_WARNING) << "DTLS-SRTP key installation failed";
   } else {
-    dtls_keyed_ = true;
     UpdateTransportOverhead();
   }
   return ret;
 }
 
 void BaseChannel::MaybeSetupDtlsSrtp_n() {
-  if (srtp_filter_.IsActive()) {
+  if (dtls_active()) {
     return;
   }
 
@@ -1039,6 +951,10 @@ void BaseChannel::MaybeSetupDtlsSrtp_n() {
     return;
   }
 
+  if (!srtp_transport_) {
+    EnableSrtpTransport_n();
+  }
+
   if (!SetupDtlsSrtp_n(false)) {
     SignalDtlsSrtpSetupFailure_n(false);
     return;
@@ -1122,6 +1038,24 @@ bool BaseChannel::CheckSrtpConfig_n(const std::vector<CryptoParams>& cryptos,
   return true;
 }
 
+void BaseChannel::EnableSrtpTransport_n() {
+  if (srtp_transport_ == nullptr) {
+    rtp_transport_->SignalReadyToSend.disconnect(this);
+    rtp_transport_->SignalPacketReceived.disconnect(this);
+
+    auto transport = rtc::MakeUnique<webrtc::SrtpTransport>(
+        std::move(rtp_transport_), content_name_);
+    srtp_transport_ = transport.get();
+    rtp_transport_ = std::move(transport);
+
+    rtp_transport_->SignalReadyToSend.connect(
+        this, &BaseChannel::OnTransportReadyToSend);
+    rtp_transport_->SignalPacketReceived.connect(
+        this, &BaseChannel::OnPacketReceived);
+    LOG(LS_INFO) << "Wrapping RtpTransport in SrtpTransport.";
+  }
+}
+
 bool BaseChannel::SetSrtp_n(const std::vector<CryptoParams>& cryptos,
                             ContentAction action,
                             ContentSource src,
@@ -1138,36 +1072,69 @@ bool BaseChannel::SetSrtp_n(const std::vector<CryptoParams>& cryptos,
   if (!ret) {
     return false;
   }
-  srtp_filter_.SetEncryptedHeaderExtensionIds(src, encrypted_extension_ids);
+
+  // If SRTP was not required, but we're setting a description that uses SDES,
+  // we need to upgrade to an SrtpTransport.
+  if (!srtp_transport_ && !dtls && !cryptos.empty()) {
+    EnableSrtpTransport_n();
+  }
+  if (srtp_transport_) {
+    srtp_transport_->SetEncryptedHeaderExtensionIds(src,
+                                                    encrypted_extension_ids);
+  }
   switch (action) {
     case CA_OFFER:
       // If DTLS is already active on the channel, we could be renegotiating
       // here. We don't update the srtp filter.
       if (!dtls) {
-        ret = srtp_filter_.SetOffer(cryptos, src);
+        ret = sdes_negotiator_.SetOffer(cryptos, src);
       }
       break;
     case CA_PRANSWER:
       // If we're doing DTLS-SRTP, we don't want to update the filter
       // with an answer, because we already have SRTP parameters.
       if (!dtls) {
-        ret = srtp_filter_.SetProvisionalAnswer(cryptos, src);
+        ret = sdes_negotiator_.SetProvisionalAnswer(cryptos, src);
       }
       break;
     case CA_ANSWER:
       // If we're doing DTLS-SRTP, we don't want to update the filter
       // with an answer, because we already have SRTP parameters.
       if (!dtls) {
-        ret = srtp_filter_.SetAnswer(cryptos, src);
+        ret = sdes_negotiator_.SetAnswer(cryptos, src);
       }
       break;
     default:
       break;
   }
+
+  // If setting an SDES answer succeeded, apply the negotiated parameters
+  // to the SRTP transport.
+  if ((action == CA_PRANSWER || action == CA_ANSWER) && !dtls && ret) {
+    if (sdes_negotiator_.send_cipher_suite() &&
+        sdes_negotiator_.recv_cipher_suite()) {
+      ret = srtp_transport_->SetRtpParams(
+          *(sdes_negotiator_.send_cipher_suite()),
+          sdes_negotiator_.send_key().data(),
+          static_cast<int>(sdes_negotiator_.send_key().size()),
+          *(sdes_negotiator_.recv_cipher_suite()),
+          sdes_negotiator_.recv_key().data(),
+          static_cast<int>(sdes_negotiator_.recv_key().size()));
+    } else {
+      LOG(LS_INFO) << "No crypto keys are provided for SDES.";
+      if (action == CA_ANSWER && srtp_transport_) {
+        // Explicitly reset the |srtp_transport_| if no crypto param is
+        // provided in the answer. No need to call |ResetParams()| for
+        // |sdes_negotiator_| because it resets the params inside |SetAnswer|.
+        srtp_transport_->ResetParams();
+      }
+    }
+  }
+
   // Only update SRTP filter if using DTLS. SDES is handled internally
   // by the SRTP filter.
   // TODO(jbauch): Only update if encrypted extension ids have changed.
-  if (ret && dtls_keyed_ && rtp_dtls_transport_ &&
+  if (ret && dtls_active() && rtp_dtls_transport_ &&
       rtp_dtls_transport_->dtls_state() == DTLS_TRANSPORT_CONNECTED) {
     bool rtcp = false;
     ret = SetupDtlsSrtp_n(rtcp);
@@ -1211,7 +1178,6 @@ bool BaseChannel::SetRtcpMux_n(bool enable,
             transport_name_.empty()
                 ? rtp_transport_->rtp_packet_transport()->debug_name()
                 : transport_name_;
-        ;
         LOG(LS_INFO) << "Enabling rtcp-mux for " << content_name()
                      << "; no longer need RTCP transport for " << debug_name;
         if (rtp_transport_->rtcp_packet_transport()) {
@@ -1440,7 +1406,13 @@ void BaseChannel::MaybeCacheRtpAbsSendTimeHeaderExtension_w(
 
 void BaseChannel::CacheRtpAbsSendTimeHeaderExtension_n(
     int rtp_abs_sendtime_extn_id) {
-  rtp_abs_sendtime_extn_id_ = rtp_abs_sendtime_extn_id;
+  if (srtp_transport_) {
+    srtp_transport_->CacheRtpAbsSendTimeHeaderExtension(
+        rtp_abs_sendtime_extn_id);
+  } else {
+    LOG(LS_WARNING) << "Trying to cache the Absolute Send Time extension id "
+                       "but the SRTP is not active.";
+  }
 }
 
 void BaseChannel::OnMessage(rtc::Message *pmsg) {
@@ -1724,9 +1696,9 @@ int BaseChannel::GetTransportOverheadPerPacket() const {
           ? kTcpOverhaed
           : kUdpOverhaed;
 
-  if (secure()) {
+  if (sdes_active()) {
     int srtp_overhead = 0;
-    if (srtp_filter_.GetSrtpOverhead(&srtp_overhead))
+    if (srtp_transport_->GetSrtpOverhead(&srtp_overhead))
       transport_overhead_per_packet += srtp_overhead;
   }
 
diff --git a/webrtc/pc/channel.h b/webrtc/pc/channel.h
index c6dc29dd08..b95bd529b0 100644
--- a/webrtc/pc/channel.h
+++ b/webrtc/pc/channel.h
@@ -33,7 +33,6 @@
 #include "webrtc/pc/mediamonitor.h"
 #include "webrtc/pc/mediasession.h"
 #include "webrtc/pc/rtcpmuxfilter.h"
-#include "webrtc/pc/rtptransportinternal.h"
 #include "webrtc/pc/srtpfilter.h"
 #include "webrtc/rtc_base/asyncinvoker.h"
 #include "webrtc/rtc_base/asyncudpsocket.h"
@@ -44,6 +43,8 @@
 
 namespace webrtc {
 class AudioSinkInterface;
+class RtpTransportInternal;
+class SrtpTransport;
 }  // namespace webrtc
 
 namespace cricket {
@@ -99,12 +100,12 @@ class BaseChannel
   const std::string& transport_name() const { return transport_name_; }
   bool enabled() const { return enabled_; }
 
-  // This function returns true if we are using SRTP.
-  bool secure() const { return srtp_filter_.IsActive(); }
-  // The following function returns true if we are using
-  // DTLS-based keying. If you turned off SRTP later, however
-  // you could have secure() == false and dtls_secure() == true.
-  bool secure_dtls() const { return dtls_keyed_; }
+  // This function returns true if we are using SDES.
+  bool sdes_active() const { return sdes_negotiator_.IsActive(); }
+  // The following function returns true if we are using DTLS-based keying.
+  bool dtls_active() const { return dtls_active_; }
+  // This function returns true if using SRTP (DTLS-based keying or SDES).
+  bool srtp_active() const { return sdes_active() || dtls_active(); }
 
   bool writable() const { return writable_; }
 
@@ -188,8 +189,6 @@ class BaseChannel
       override;
   int SetOption_n(SocketType type, rtc::Socket::Option o, int val);
 
-  SrtpFilter* srtp_filter() { return &srtp_filter_; }
-
   virtual cricket::MediaType media_type() = 0;
 
   // This function returns true if we require SRTP for call setup.
@@ -378,6 +377,8 @@ class BaseChannel
   void CacheRtpAbsSendTimeHeaderExtension_n(int rtp_abs_sendtime_extn_id);
   int GetTransportOverheadPerPacket() const;
   void UpdateTransportOverhead();
+  // Wraps the existing RtpTransport in an SrtpTransport.
+  void EnableSrtpTransport_n();
 
   rtc::Thread* const worker_thread_;
   rtc::Thread* const network_thread_;
@@ -398,16 +399,16 @@ class BaseChannel
   DtlsTransportInternal* rtp_dtls_transport_ = nullptr;
   DtlsTransportInternal* rtcp_dtls_transport_ = nullptr;
   std::unique_ptr<webrtc::RtpTransportInternal> rtp_transport_;
+  webrtc::SrtpTransport* srtp_transport_ = nullptr;
   std::vector<std::pair<rtc::Socket::Option, int> > socket_options_;
   std::vector<std::pair<rtc::Socket::Option, int> > rtcp_socket_options_;
-  SrtpFilter srtp_filter_;
+  SrtpFilter sdes_negotiator_;
   RtcpMuxFilter rtcp_mux_filter_;
   bool writable_ = false;
   bool was_ever_writable_ = false;
   bool has_received_packet_ = false;
-  bool dtls_keyed_ = false;
+  bool dtls_active_ = false;
   const bool srtp_required_ = true;
-  int rtp_abs_sendtime_extn_id_ = -1;
 
   // MediaChannel related members that should be accessed from the worker
   // thread.
diff --git a/webrtc/pc/channel_unittest.cc b/webrtc/pc/channel_unittest.cc
index 3f30201874..ae34a12de4 100644
--- a/webrtc/pc/channel_unittest.cc
+++ b/webrtc/pc/channel_unittest.cc
@@ -581,7 +581,7 @@ class ChannelTest : public testing::Test, public sigslot::has_slots<> {
   // Basic sanity check.
   void TestInit() {
     CreateChannels(0, 0);
-    EXPECT_FALSE(channel1_->secure());
+    EXPECT_FALSE(channel1_->srtp_active());
     EXPECT_FALSE(media_channel1_->sending());
     if (verify_playout_) {
       EXPECT_FALSE(media_channel1_->playout());
@@ -896,8 +896,8 @@ class ChannelTest : public testing::Test, public sigslot::has_slots<> {
     EXPECT_TRUE(channel2_->SetRemoteContent(&content4, CA_ANSWER, NULL));
     EXPECT_EQ(0u, media_channel2_->recv_streams().size());
 
-    EXPECT_TRUE(channel1_->secure());
-    EXPECT_TRUE(channel2_->secure());
+    EXPECT_TRUE(channel1_->srtp_active());
+    EXPECT_TRUE(channel2_->srtp_active());
     SendCustomRtp2(kSsrc2, 0);
     WaitForThreads();
     EXPECT_TRUE(CheckCustomRtp1(kSsrc2, 0));
@@ -1253,14 +1253,14 @@ class ChannelTest : public testing::Test, public sigslot::has_slots<> {
   // Test setting up a call.
   void TestCallSetup() {
     CreateChannels(0, 0);
-    EXPECT_FALSE(channel1_->secure());
+    EXPECT_FALSE(channel1_->srtp_active());
     EXPECT_TRUE(SendInitiate());
     if (verify_playout_) {
       EXPECT_TRUE(media_channel1_->playout());
     }
     EXPECT_FALSE(media_channel1_->sending());
     EXPECT_TRUE(SendAccept());
-    EXPECT_FALSE(channel1_->secure());
+    EXPECT_FALSE(channel1_->srtp_active());
     EXPECT_TRUE(media_channel1_->sending());
     EXPECT_EQ(1U, media_channel1_->codecs().size());
     if (verify_playout_) {
@@ -1535,17 +1535,17 @@ class ChannelTest : public testing::Test, public sigslot::has_slots<> {
     bool dtls1 = !!(flags1_in & DTLS);
     bool dtls2 = !!(flags2_in & DTLS);
     CreateChannels(flags1, flags2);
-    EXPECT_FALSE(channel1_->secure());
-    EXPECT_FALSE(channel2_->secure());
+    EXPECT_FALSE(channel1_->srtp_active());
+    EXPECT_FALSE(channel2_->srtp_active());
     EXPECT_TRUE(SendInitiate());
     WaitForThreads();
     EXPECT_TRUE(channel1_->writable());
     EXPECT_TRUE(channel2_->writable());
     EXPECT_TRUE(SendAccept());
-    EXPECT_TRUE(channel1_->secure());
-    EXPECT_TRUE(channel2_->secure());
-    EXPECT_EQ(dtls1 && dtls2, channel1_->secure_dtls());
-    EXPECT_EQ(dtls1 && dtls2, channel2_->secure_dtls());
+    EXPECT_TRUE(channel1_->srtp_active());
+    EXPECT_TRUE(channel2_->srtp_active());
+    EXPECT_EQ(dtls1 && dtls2, channel1_->dtls_active());
+    EXPECT_EQ(dtls1 && dtls2, channel2_->dtls_active());
     SendRtp1();
     SendRtp2();
     SendRtcp1();
@@ -1564,12 +1564,12 @@ class ChannelTest : public testing::Test, public sigslot::has_slots<> {
   // Test that we properly handling SRTP negotiating down to RTP.
   void SendSrtpToRtp() {
     CreateChannels(SECURE, 0);
-    EXPECT_FALSE(channel1_->secure());
-    EXPECT_FALSE(channel2_->secure());
+    EXPECT_FALSE(channel1_->srtp_active());
+    EXPECT_FALSE(channel2_->srtp_active());
     EXPECT_TRUE(SendInitiate());
     EXPECT_TRUE(SendAccept());
-    EXPECT_FALSE(channel1_->secure());
-    EXPECT_FALSE(channel2_->secure());
+    EXPECT_FALSE(channel1_->srtp_active());
+    EXPECT_FALSE(channel2_->srtp_active());
     SendRtp1();
     SendRtp2();
     SendRtcp1();
@@ -1594,8 +1594,8 @@ class ChannelTest : public testing::Test, public sigslot::has_slots<> {
                      SSRC_MUX | RTCP_MUX | SECURE);
       EXPECT_TRUE(SendOffer());
       EXPECT_TRUE(SendProvisionalAnswer());
-      EXPECT_TRUE(channel1_->secure());
-      EXPECT_TRUE(channel2_->secure());
+      EXPECT_TRUE(channel1_->srtp_active());
+      EXPECT_TRUE(channel2_->srtp_active());
       EXPECT_TRUE(channel1_->NeedsRtcpTransport());
       EXPECT_TRUE(channel2_->NeedsRtcpTransport());
       WaitForThreads();  // Wait for 'sending' flag go through network thread.
@@ -1620,8 +1620,8 @@ class ChannelTest : public testing::Test, public sigslot::has_slots<> {
       EXPECT_FALSE(channel2_->NeedsRtcpTransport());
       EXPECT_EQ(1, rtcp_mux_activated_callbacks1_);
       EXPECT_EQ(1, rtcp_mux_activated_callbacks2_);
-      EXPECT_TRUE(channel1_->secure());
-      EXPECT_TRUE(channel2_->secure());
+      EXPECT_TRUE(channel1_->srtp_active());
+      EXPECT_TRUE(channel2_->srtp_active());
       SendCustomRtcp1(kSsrc1);
       SendCustomRtp1(kSsrc1, ++sequence_number1_1);
       SendCustomRtcp2(kSsrc2);
diff --git a/webrtc/pc/rtptransport.cc b/webrtc/pc/rtptransport.cc
index ac57eb887b..b26783260f 100644
--- a/webrtc/pc/rtptransport.cc
+++ b/webrtc/pc/rtptransport.cc
@@ -76,6 +76,18 @@ bool RtpTransport::IsWritable(bool rtcp) const {
   return transport && transport->writable();
 }
 
+bool RtpTransport::SendRtpPacket(rtc::CopyOnWriteBuffer* packet,
+                                 const rtc::PacketOptions& options,
+                                 int flags) {
+  return SendPacket(false, packet, options, flags);
+}
+
+bool RtpTransport::SendRtcpPacket(rtc::CopyOnWriteBuffer* packet,
+                                  const rtc::PacketOptions& options,
+                                  int flags) {
+  return SendPacket(true, packet, options, flags);
+}
+
 bool RtpTransport::SendPacket(bool rtcp,
                               rtc::CopyOnWriteBuffer* packet,
                               const rtc::PacketOptions& options,
diff --git a/webrtc/pc/rtptransport.h b/webrtc/pc/rtptransport.h
index 8b408cabfa..94c5877142 100644
--- a/webrtc/pc/rtptransport.h
+++ b/webrtc/pc/rtptransport.h
@@ -56,10 +56,13 @@ class RtpTransport : public RtpTransportInternal {
 
   bool IsWritable(bool rtcp) const override;
 
-  bool SendPacket(bool rtcp,
-                  rtc::CopyOnWriteBuffer* packet,
-                  const rtc::PacketOptions& options,
-                  int flags) override;
+  bool SendRtpPacket(rtc::CopyOnWriteBuffer* packet,
+                     const rtc::PacketOptions& options,
+                     int flags) override;
+
+  bool SendRtcpPacket(rtc::CopyOnWriteBuffer* packet,
+                      const rtc::PacketOptions& options,
+                      int flags) override;
 
   bool HandlesPayloadType(int payload_type) const override;
 
@@ -80,6 +83,11 @@ class RtpTransport : public RtpTransportInternal {
 
   void MaybeSignalReadyToSend();
 
+  bool SendPacket(bool rtcp,
+                  rtc::CopyOnWriteBuffer* packet,
+                  const rtc::PacketOptions& options,
+                  int flags);
+
   void OnReadPacket(rtc::PacketTransportInternal* transport,
                     const char* data,
                     size_t len,
diff --git a/webrtc/pc/rtptransportinternal.h b/webrtc/pc/rtptransportinternal.h
index fd94d8e8f0..684afc4e67 100644
--- a/webrtc/pc/rtptransportinternal.h
+++ b/webrtc/pc/rtptransportinternal.h
@@ -54,10 +54,13 @@ class RtpTransportInternal : public RtpTransportInterface,
 
   virtual bool IsWritable(bool rtcp) const = 0;
 
-  virtual bool SendPacket(bool rtcp,
-                          rtc::CopyOnWriteBuffer* packet,
-                          const rtc::PacketOptions& options,
-                          int flags) = 0;
+  virtual bool SendRtpPacket(rtc::CopyOnWriteBuffer* packet,
+                             const rtc::PacketOptions& options,
+                             int flags) = 0;
+
+  virtual bool SendRtcpPacket(rtc::CopyOnWriteBuffer* packet,
+                              const rtc::PacketOptions& options,
+                              int flags) = 0;
 
   virtual bool HandlesPayloadType(int payload_type) const = 0;
 
diff --git a/webrtc/pc/srtpfilter.cc b/webrtc/pc/srtpfilter.cc
index dde84bc14e..560dac8f82 100644
--- a/webrtc/pc/srtpfilter.cc
+++ b/webrtc/pc/srtpfilter.cc
@@ -17,7 +17,6 @@
 #include "webrtc/media/base/rtputils.h"
 #include "webrtc/pc/srtpsession.h"
 #include "webrtc/rtc_base/base64.h"
-#include "webrtc/rtc_base/buffer.h"
 #include "webrtc/rtc_base/byteorder.h"
 #include "webrtc/rtc_base/checks.h"
 #include "webrtc/rtc_base/logging.h"
@@ -63,209 +62,6 @@ bool SrtpFilter::SetProvisionalAnswer(
   return DoSetAnswer(answer_params, source, false);
 }
 
-bool SrtpFilter::SetRtpParams(int send_cs,
-                              const uint8_t* send_key,
-                              int send_key_len,
-                              int recv_cs,
-                              const uint8_t* recv_key,
-                              int recv_key_len) {
-  if (IsActive()) {
-    LOG(LS_ERROR) << "Tried to set SRTP Params when filter already active";
-    return false;
-  }
-  CreateSrtpSessions();
-  send_session_->SetEncryptedHeaderExtensionIds(
-      send_encrypted_header_extension_ids_);
-  if (!send_session_->SetSend(send_cs, send_key, send_key_len)) {
-    return false;
-  }
-
-  recv_session_->SetEncryptedHeaderExtensionIds(
-      recv_encrypted_header_extension_ids_);
-  if (!recv_session_->SetRecv(recv_cs, recv_key, recv_key_len)) {
-    return false;
-  }
-
-  state_ = ST_ACTIVE;
-
-  LOG(LS_INFO) << "SRTP activated with negotiated parameters:"
-               << " send cipher_suite " << send_cs
-               << " recv cipher_suite " << recv_cs;
-  return true;
-}
-
-bool SrtpFilter::UpdateRtpParams(int send_cs,
-                                 const uint8_t* send_key,
-                                 int send_key_len,
-                                 int recv_cs,
-                                 const uint8_t* recv_key,
-                                 int recv_key_len) {
-  if (!IsActive()) {
-    LOG(LS_ERROR) << "Tried to update SRTP Params when filter is not active";
-    return false;
-  }
-  send_session_->SetEncryptedHeaderExtensionIds(
-      send_encrypted_header_extension_ids_);
-  if (!send_session_->UpdateSend(send_cs, send_key, send_key_len)) {
-    return false;
-  }
-
-  recv_session_->SetEncryptedHeaderExtensionIds(
-      recv_encrypted_header_extension_ids_);
-  if (!recv_session_->UpdateRecv(recv_cs, recv_key, recv_key_len)) {
-    return false;
-  }
-
-  LOG(LS_INFO) << "SRTP updated with negotiated parameters:"
-               << " send cipher_suite " << send_cs
-               << " recv cipher_suite " << recv_cs;
-  return true;
-}
-
-// This function is provided separately because DTLS-SRTP behaves
-// differently in RTP/RTCP mux and non-mux modes.
-//
-// - In the non-muxed case, RTP and RTCP are keyed with different
-//   keys (from different DTLS handshakes), and so we need a new
-//   SrtpSession.
-// - In the muxed case, they are keyed with the same keys, so
-//   this function is not needed
-bool SrtpFilter::SetRtcpParams(int send_cs,
-                               const uint8_t* send_key,
-                               int send_key_len,
-                               int recv_cs,
-                               const uint8_t* recv_key,
-                               int recv_key_len) {
-  // This can only be called once, but can be safely called after
-  // SetRtpParams
-  if (send_rtcp_session_ || recv_rtcp_session_) {
-    LOG(LS_ERROR) << "Tried to set SRTCP Params when filter already active";
-    return false;
-  }
-
-  send_rtcp_session_.reset(new SrtpSession());
-  if (!send_rtcp_session_->SetRecv(send_cs, send_key, send_key_len)) {
-    return false;
-  }
-
-  recv_rtcp_session_.reset(new SrtpSession());
-  if (!recv_rtcp_session_->SetRecv(recv_cs, recv_key, recv_key_len)) {
-    return false;
-  }
-
-  LOG(LS_INFO) << "SRTCP activated with negotiated parameters:"
-               << " send cipher_suite " << send_cs
-               << " recv cipher_suite " << recv_cs;
-
-  return true;
-}
-
-bool SrtpFilter::ProtectRtp(void* p, int in_len, int max_len, int* out_len) {
-  if (!IsActive()) {
-    LOG(LS_WARNING) << "Failed to ProtectRtp: SRTP not active";
-    return false;
-  }
-  RTC_CHECK(send_session_);
-  return send_session_->ProtectRtp(p, in_len, max_len, out_len);
-}
-
-bool SrtpFilter::ProtectRtp(void* p,
-                            int in_len,
-                            int max_len,
-                            int* out_len,
-                            int64_t* index) {
-  if (!IsActive()) {
-    LOG(LS_WARNING) << "Failed to ProtectRtp: SRTP not active";
-    return false;
-  }
-  RTC_CHECK(send_session_);
-  return send_session_->ProtectRtp(p, in_len, max_len, out_len, index);
-}
-
-bool SrtpFilter::ProtectRtcp(void* p, int in_len, int max_len, int* out_len) {
-  if (!IsActive()) {
-    LOG(LS_WARNING) << "Failed to ProtectRtcp: SRTP not active";
-    return false;
-  }
-  if (send_rtcp_session_) {
-    return send_rtcp_session_->ProtectRtcp(p, in_len, max_len, out_len);
-  } else {
-    RTC_CHECK(send_session_);
-    return send_session_->ProtectRtcp(p, in_len, max_len, out_len);
-  }
-}
-
-bool SrtpFilter::UnprotectRtp(void* p, int in_len, int* out_len) {
-  if (!IsActive()) {
-    LOG(LS_WARNING) << "Failed to UnprotectRtp: SRTP not active";
-    return false;
-  }
-  RTC_CHECK(recv_session_);
-  return recv_session_->UnprotectRtp(p, in_len, out_len);
-}
-
-bool SrtpFilter::UnprotectRtcp(void* p, int in_len, int* out_len) {
-  if (!IsActive()) {
-    LOG(LS_WARNING) << "Failed to UnprotectRtcp: SRTP not active";
-    return false;
-  }
-  if (recv_rtcp_session_) {
-    return recv_rtcp_session_->UnprotectRtcp(p, in_len, out_len);
-  } else {
-    RTC_CHECK(recv_session_);
-    return recv_session_->UnprotectRtcp(p, in_len, out_len);
-  }
-}
-
-bool SrtpFilter::GetRtpAuthParams(uint8_t** key, int* key_len, int* tag_len) {
-  if (!IsActive()) {
-    LOG(LS_WARNING) << "Failed to GetRtpAuthParams: SRTP not active";
-    return false;
-  }
-
-  RTC_CHECK(send_session_);
-  return send_session_->GetRtpAuthParams(key, key_len, tag_len);
-}
-
-bool SrtpFilter::GetSrtpOverhead(int* srtp_overhead) const {
-  if (!IsActive()) {
-    LOG(LS_WARNING) << "Failed to GetSrtpOverhead: SRTP not active";
-    return false;
-  }
-
-  RTC_CHECK(send_session_);
-  *srtp_overhead = send_session_->GetSrtpOverhead();
-  return true;
-}
-
-void SrtpFilter::EnableExternalAuth() {
-  RTC_DCHECK(!IsActive());
-  external_auth_enabled_ = true;
-}
-
-bool SrtpFilter::IsExternalAuthEnabled() const {
-  return external_auth_enabled_;
-}
-
-bool SrtpFilter::IsExternalAuthActive() const {
-  if (!IsActive()) {
-    LOG(LS_WARNING) << "Failed to check IsExternalAuthActive: SRTP not active";
-    return false;
-  }
-
-  RTC_CHECK(send_session_);
-  return send_session_->IsExternalAuthActive();
-}
-
-void SrtpFilter::SetEncryptedHeaderExtensionIds(ContentSource source,
-    const std::vector<int>& extension_ids) {
-  if (source == CS_LOCAL) {
-    recv_encrypted_header_extension_ids_ = extension_ids;
-  } else {
-    send_encrypted_header_extension_ids_ = extension_ids;
-  }
-}
-
 bool SrtpFilter::ExpectOffer(ContentSource source) {
   return ((state_ == ST_INIT) ||
           (state_ == ST_ACTIVE) ||
@@ -323,13 +119,16 @@ bool SrtpFilter::DoSetAnswer(const std::vector<CryptoParams>& answer_params,
   CryptoParams selected_params;
   if (!NegotiateParams(answer_params, &selected_params))
     return false;
-  const CryptoParams& send_params =
+
+  const CryptoParams& new_send_params =
       (source == CS_REMOTE) ? selected_params : answer_params[0];
-  const CryptoParams& recv_params =
+  const CryptoParams& new_recv_params =
       (source == CS_REMOTE) ? answer_params[0] : selected_params;
-  if (!ApplyParams(send_params, recv_params)) {
+  if (!ApplySendParams(new_send_params) || !ApplyRecvParams(new_recv_params)) {
     return false;
   }
+  applied_send_params_ = new_send_params;
+  applied_recv_params_ = new_recv_params;
 
   if (final) {
     offer_params_.clear();
@@ -341,17 +140,6 @@ bool SrtpFilter::DoSetAnswer(const std::vector<CryptoParams>& answer_params,
   return true;
 }
 
-void SrtpFilter::CreateSrtpSessions() {
-  send_session_.reset(new SrtpSession());
-  applied_send_params_ = CryptoParams();
-  recv_session_.reset(new SrtpSession());
-  applied_recv_params_ = CryptoParams();
-
-  if (external_auth_enabled_) {
-    send_session_->EnableExternalAuth();
-  }
-}
-
 bool SrtpFilter::NegotiateParams(const std::vector<CryptoParams>& answer_params,
                                  CryptoParams* selected_params) {
   // We're processing an accept. We should have exactly one set of params,
@@ -379,85 +167,76 @@ bool SrtpFilter::NegotiateParams(const std::vector<CryptoParams>& answer_params,
   return ret;
 }
 
-bool SrtpFilter::ApplyParams(const CryptoParams& send_params,
-                             const CryptoParams& recv_params) {
-  // TODO(jiayl): Split this method to apply send and receive CryptoParams
-  // independently, so that we can skip one method when either send or receive
-  // CryptoParams is unchanged.
+bool SrtpFilter::ResetParams() {
+  offer_params_.clear();
+  applied_send_params_ = CryptoParams();
+  applied_recv_params_ = CryptoParams();
+  send_cipher_suite_ = rtc::Optional<int>();
+  recv_cipher_suite_ = rtc::Optional<int>();
+  send_key_.Clear();
+  recv_key_.Clear();
+  state_ = ST_INIT;
+  return true;
+}
+
+bool SrtpFilter::ApplySendParams(const CryptoParams& send_params) {
   if (applied_send_params_.cipher_suite == send_params.cipher_suite &&
-      applied_send_params_.key_params == send_params.key_params &&
-      applied_recv_params_.cipher_suite == recv_params.cipher_suite &&
-      applied_recv_params_.key_params == recv_params.key_params) {
-    LOG(LS_INFO) << "Applying the same SRTP parameters again. No-op.";
+      applied_send_params_.key_params == send_params.key_params) {
+    LOG(LS_INFO) << "Applying the same SRTP send parameters again. No-op.";
 
     // We do not want to reset the ROC if the keys are the same. So just return.
     return true;
   }
 
-  int send_suite = rtc::SrtpCryptoSuiteFromName(send_params.cipher_suite);
-  int recv_suite = rtc::SrtpCryptoSuiteFromName(recv_params.cipher_suite);
-  if (send_suite == rtc::SRTP_INVALID_CRYPTO_SUITE ||
-      recv_suite == rtc::SRTP_INVALID_CRYPTO_SUITE) {
+  send_cipher_suite_ = rtc::Optional<int>(
+      rtc::SrtpCryptoSuiteFromName(send_params.cipher_suite));
+  if (send_cipher_suite_ == rtc::SRTP_INVALID_CRYPTO_SUITE) {
     LOG(LS_WARNING) << "Unknown crypto suite(s) received:"
-                    << " send cipher_suite " << send_params.cipher_suite
-                    << " recv cipher_suite " << recv_params.cipher_suite;
+                    << " send cipher_suite " << send_params.cipher_suite;
     return false;
   }
 
   int send_key_len, send_salt_len;
-  int recv_key_len, recv_salt_len;
-  if (!rtc::GetSrtpKeyAndSaltLengths(send_suite, &send_key_len,
-                                     &send_salt_len) ||
-      !rtc::GetSrtpKeyAndSaltLengths(recv_suite, &recv_key_len,
-                                     &recv_salt_len)) {
+  if (!rtc::GetSrtpKeyAndSaltLengths(*send_cipher_suite_, &send_key_len,
+                                     &send_salt_len)) {
     LOG(LS_WARNING) << "Could not get lengths for crypto suite(s):"
-                    << " send cipher_suite " << send_params.cipher_suite
+                    << " send cipher_suite " << send_params.cipher_suite;
+    return false;
+  }
+
+  send_key_ = rtc::Buffer(send_key_len + send_salt_len);
+  return ParseKeyParams(send_params.key_params, send_key_.data(),
+                        send_key_.size());
+}
+
+bool SrtpFilter::ApplyRecvParams(const CryptoParams& recv_params) {
+  if (applied_recv_params_.cipher_suite == recv_params.cipher_suite &&
+      applied_recv_params_.key_params == recv_params.key_params) {
+    LOG(LS_INFO) << "Applying the same SRTP recv parameters again. No-op.";
+
+    // We do not want to reset the ROC if the keys are the same. So just return.
+    return true;
+  }
+
+  recv_cipher_suite_ = rtc::Optional<int>(
+      rtc::SrtpCryptoSuiteFromName(recv_params.cipher_suite));
+  if (recv_cipher_suite_ == rtc::SRTP_INVALID_CRYPTO_SUITE) {
+    LOG(LS_WARNING) << "Unknown crypto suite(s) received:"
                     << " recv cipher_suite " << recv_params.cipher_suite;
     return false;
   }
 
-  // TODO(juberti): Zero these buffers after use.
-  bool ret;
-  rtc::Buffer send_key(send_key_len + send_salt_len);
-  rtc::Buffer recv_key(recv_key_len + recv_salt_len);
-  ret = (ParseKeyParams(send_params.key_params, send_key.data(),
-                        send_key.size()) &&
-         ParseKeyParams(recv_params.key_params, recv_key.data(),
-                        recv_key.size()));
-  if (ret) {
-    CreateSrtpSessions();
-    send_session_->SetEncryptedHeaderExtensionIds(
-        send_encrypted_header_extension_ids_);
-    recv_session_->SetEncryptedHeaderExtensionIds(
-        recv_encrypted_header_extension_ids_);
-    ret = (send_session_->SetSend(
-               rtc::SrtpCryptoSuiteFromName(send_params.cipher_suite),
-               send_key.data(), send_key.size()) &&
-           recv_session_->SetRecv(
-               rtc::SrtpCryptoSuiteFromName(recv_params.cipher_suite),
-               recv_key.data(), recv_key.size()));
+  int recv_key_len, recv_salt_len;
+  if (!rtc::GetSrtpKeyAndSaltLengths(*recv_cipher_suite_, &recv_key_len,
+                                     &recv_salt_len)) {
+    LOG(LS_WARNING) << "Could not get lengths for crypto suite(s):"
+                    << " recv cipher_suite " << recv_params.cipher_suite;
+    return false;
   }
-  if (ret) {
-    LOG(LS_INFO) << "SRTP activated with negotiated parameters:"
-                 << " send cipher_suite " << send_params.cipher_suite
-                 << " recv cipher_suite " << recv_params.cipher_suite;
-    applied_send_params_ = send_params;
-    applied_recv_params_ = recv_params;
-  } else {
-    LOG(LS_WARNING) << "Failed to apply negotiated SRTP parameters";
-  }
-  return ret;
-}
 
-bool SrtpFilter::ResetParams() {
-  offer_params_.clear();
-  state_ = ST_INIT;
-  send_session_ = nullptr;
-  recv_session_ = nullptr;
-  send_rtcp_session_ = nullptr;
-  recv_rtcp_session_ = nullptr;
-  LOG(LS_INFO) << "SRTP reset to init state";
-  return true;
+  recv_key_ = rtc::Buffer(recv_key_len + recv_salt_len);
+  return ParseKeyParams(recv_params.key_params, recv_key_.data(),
+                        recv_key_.size());
 }
 
 bool SrtpFilter::ParseKeyParams(const std::string& key_params,
@@ -472,8 +251,9 @@ bool SrtpFilter::ParseKeyParams(const std::string& key_params,
 
   // Fail if base64 decode fails, or the key is the wrong size.
   std::string key_b64(key_params.substr(7)), key_str;
-  if (!rtc::Base64::Decode(key_b64, rtc::Base64::DO_STRICT,
-                           &key_str, nullptr) || key_str.size() != len) {
+  if (!rtc::Base64::Decode(key_b64, rtc::Base64::DO_STRICT, &key_str,
+                           nullptr) ||
+      key_str.size() != len) {
     return false;
   }
 
diff --git a/webrtc/pc/srtpfilter.h b/webrtc/pc/srtpfilter.h
index 15fdae9582..619aaa37d5 100644
--- a/webrtc/pc/srtpfilter.h
+++ b/webrtc/pc/srtpfilter.h
@@ -20,8 +20,10 @@
 #include "webrtc/media/base/cryptoparams.h"
 #include "webrtc/p2p/base/sessiondescription.h"
 #include "webrtc/rtc_base/basictypes.h"
+#include "webrtc/rtc_base/buffer.h"
 #include "webrtc/rtc_base/constructormagic.h"
 #include "webrtc/rtc_base/criticalsection.h"
+#include "webrtc/rtc_base/optional.h"
 #include "webrtc/rtc_base/sslstreamadapter.h"
 #include "webrtc/rtc_base/thread_checker.h"
 
@@ -31,15 +33,10 @@ struct srtp_ctx_t_;
 
 namespace cricket {
 
-class SrtpSession;
-
 void ShutdownSrtp();
 
-// Class to transform SRTP to/from RTP.
-// Initialize by calling SetSend with the local security params, then call
-// SetRecv once the remote security params are received. At that point
-// Protect/UnprotectRt(c)p can be called to encrypt/decrypt data.
-// TODO: Figure out concurrency policy for SrtpFilter.
+// A helper class used to negotiate SDES crypto params.
+// TODO(zhihuang): Find a better name for this class, like "SdesNegotiator".
 class SrtpFilter {
  public:
   enum Mode {
@@ -76,85 +73,38 @@ class SrtpFilter {
   bool SetAnswer(const std::vector<CryptoParams>& answer_params,
                  ContentSource source);
 
-  // Set the header extension ids that should be encrypted for the given source.
-  void SetEncryptedHeaderExtensionIds(ContentSource source,
-      const std::vector<int>& extension_ids);
-
-  // Just set up both sets of keys directly.
-  // Used with DTLS-SRTP.
-  bool SetRtpParams(int send_cs,
-                    const uint8_t* send_key,
-                    int send_key_len,
-                    int recv_cs,
-                    const uint8_t* recv_key,
-                    int recv_key_len);
-  bool UpdateRtpParams(int send_cs,
-                       const uint8_t* send_key,
-                       int send_key_len,
-                       int recv_cs,
-                       const uint8_t* recv_key,
-                       int recv_key_len);
-  bool SetRtcpParams(int send_cs,
-                     const uint8_t* send_key,
-                     int send_key_len,
-                     int recv_cs,
-                     const uint8_t* recv_key,
-                     int recv_key_len);
-
-  // Encrypts/signs an individual RTP/RTCP packet, in-place.
-  // If an HMAC is used, this will increase the packet size.
-  bool ProtectRtp(void* data, int in_len, int max_len, int* out_len);
-  // Overloaded version, outputs packet index.
-  bool ProtectRtp(void* data,
-                  int in_len,
-                  int max_len,
-                  int* out_len,
-                  int64_t* index);
-  bool ProtectRtcp(void* data, int in_len, int max_len, int* out_len);
-  // Decrypts/verifies an invidiual RTP/RTCP packet.
-  // If an HMAC is used, this will decrease the packet size.
-  bool UnprotectRtp(void* data, int in_len, int* out_len);
-  bool UnprotectRtcp(void* data, int in_len, int* out_len);
-
-  // Returns rtp auth params from srtp context.
-  bool GetRtpAuthParams(uint8_t** key, int* key_len, int* tag_len);
-
-  // Returns srtp overhead for rtp packets.
-  bool GetSrtpOverhead(int* srtp_overhead) const;
-
-  // If external auth is enabled, SRTP will write a dummy auth tag that then
-  // later must get replaced before the packet is sent out. Only supported for
-  // non-GCM cipher suites and can be checked through "IsExternalAuthActive"
-  // if it is actually used. This method is only valid before the RTP params
-  // have been set.
-  void EnableExternalAuth();
-  bool IsExternalAuthEnabled() const;
-
-  // A SRTP filter supports external creation of the auth tag if a non-GCM
-  // cipher is used. This method is only valid after the RTP params have
-  // been set.
-  bool IsExternalAuthActive() const;
-
   bool ResetParams();
 
+  rtc::Optional<int> send_cipher_suite() { return send_cipher_suite_; }
+  rtc::Optional<int> recv_cipher_suite() { return recv_cipher_suite_; }
+
+  const rtc::Buffer& send_key() { return send_key_; }
+  const rtc::Buffer& recv_key() { return recv_key_; }
+
  protected:
   bool ExpectOffer(ContentSource source);
+
   bool StoreParams(const std::vector<CryptoParams>& params,
                    ContentSource source);
+
   bool ExpectAnswer(ContentSource source);
+
   bool DoSetAnswer(const std::vector<CryptoParams>& answer_params,
-                     ContentSource source,
-                     bool final);
-  void CreateSrtpSessions();
+                   ContentSource source,
+                   bool final);
+
   bool NegotiateParams(const std::vector<CryptoParams>& answer_params,
                        CryptoParams* selected_params);
-  bool ApplyParams(const CryptoParams& send_params,
-                   const CryptoParams& recv_params);
+
+ private:
+  bool ApplySendParams(const CryptoParams& send_params);
+
+  bool ApplyRecvParams(const CryptoParams& recv_params);
+
   static bool ParseKeyParams(const std::string& params,
                              uint8_t* key,
                              size_t len);
 
- private:
   enum State {
     ST_INIT,           // SRTP filter unused.
     ST_SENTOFFER,      // Offer with SRTP parameters sent.
@@ -179,16 +129,13 @@ class SrtpFilter {
     ST_RECEIVEDPRANSWER
   };
   State state_ = ST_INIT;
-  bool external_auth_enabled_ = false;
   std::vector<CryptoParams> offer_params_;
-  std::unique_ptr<SrtpSession> send_session_;
-  std::unique_ptr<SrtpSession> recv_session_;
-  std::unique_ptr<SrtpSession> send_rtcp_session_;
-  std::unique_ptr<SrtpSession> recv_rtcp_session_;
   CryptoParams applied_send_params_;
   CryptoParams applied_recv_params_;
-  std::vector<int> send_encrypted_header_extension_ids_;
-  std::vector<int> recv_encrypted_header_extension_ids_;
+  rtc::Optional<int> send_cipher_suite_;
+  rtc::Optional<int> recv_cipher_suite_;
+  rtc::Buffer send_key_;
+  rtc::Buffer recv_key_;
 };
 
 }  // namespace cricket
diff --git a/webrtc/pc/srtpfilter_unittest.cc b/webrtc/pc/srtpfilter_unittest.cc
index 3f6f008a11..c4ad305afe 100644
--- a/webrtc/pc/srtpfilter_unittest.cc
+++ b/webrtc/pc/srtpfilter_unittest.cc
@@ -13,14 +13,7 @@
 #include "webrtc/pc/srtpfilter.h"
 
 #include "webrtc/media/base/cryptoparams.h"
-#include "webrtc/media/base/fakertp.h"
-#include "webrtc/p2p/base/sessiondescription.h"
-#include "webrtc/pc/srtptestutil.h"
-#include "webrtc/rtc_base/buffer.h"
-#include "webrtc/rtc_base/byteorder.h"
-#include "webrtc/rtc_base/constructormagic.h"
 #include "webrtc/rtc_base/gunit.h"
-#include "webrtc/rtc_base/thread.h"
 
 using cricket::CryptoParams;
 using cricket::CS_LOCAL;
@@ -28,14 +21,6 @@ using cricket::CS_REMOTE;
 
 namespace rtc {
 
-static const uint8_t kTestKeyGcm128_1[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ12";
-static const uint8_t kTestKeyGcm128_2[] = "21ZYXWVUTSRQPONMLKJIHGFEDCBA";
-static const int kTestKeyGcm128Len = 28;  // 128 bits key + 96 bits salt.
-static const uint8_t kTestKeyGcm256_1[] =
-    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqr";
-static const uint8_t kTestKeyGcm256_2[] =
-    "rqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA";
-static const int kTestKeyGcm256Len = 44;  // 256 bits key + 96 bits salt.
 static const std::string kTestKeyParams1 =
     "inline:WVNfX19zZW1jdGwgKCkgewkyMjA7fQp9CnVubGVz";
 static const std::string kTestKeyParams2 =
@@ -67,15 +52,13 @@ static const cricket::CryptoParams kTestCryptoParamsGcm4(
 
 class SrtpFilterTest : public testing::Test {
  protected:
-  SrtpFilterTest()
-  // Need to initialize |sequence_number_|, the value does not matter.
-      : sequence_number_(1) {
-  }
+  SrtpFilterTest() {}
   static std::vector<CryptoParams> MakeVector(const CryptoParams& params) {
     std::vector<CryptoParams> vec;
     vec.push_back(params);
     return vec;
   }
+
   void TestSetParams(const std::vector<CryptoParams>& params1,
                      const std::vector<CryptoParams>& params2) {
     EXPECT_TRUE(f1_.SetOffer(params1, CS_LOCAL));
@@ -87,184 +70,16 @@ class SrtpFilterTest : public testing::Test {
     EXPECT_TRUE(f1_.IsActive());
     EXPECT_TRUE(f2_.IsActive());
   }
-  void TestRtpAuthParams(cricket::SrtpFilter* filter, const std::string& cs) {
-    int overhead;
-    EXPECT_TRUE(filter->GetSrtpOverhead(&overhead));
-    switch (SrtpCryptoSuiteFromName(cs)) {
-      case SRTP_AES128_CM_SHA1_32:
-        EXPECT_EQ(32/8, overhead);  // 32-bit tag.
-        break;
-      case SRTP_AES128_CM_SHA1_80:
-        EXPECT_EQ(80/8, overhead);  // 80-bit tag.
-        break;
-      default:
-        RTC_NOTREACHED();
-        break;
-    }
 
-    uint8_t* auth_key = nullptr;
-    int key_len = 0;
-    int tag_len = 0;
-    EXPECT_TRUE(filter->GetRtpAuthParams(&auth_key, &key_len, &tag_len));
-    EXPECT_NE(nullptr, auth_key);
-    EXPECT_EQ(160/8, key_len);  // Length of SHA-1 is 160 bits.
-    EXPECT_EQ(overhead, tag_len);
+  void VerifyCryptoParamsMatch(const std::string& cs1, const std::string& cs2) {
+    EXPECT_EQ(rtc::SrtpCryptoSuiteFromName(cs1), f1_.send_cipher_suite());
+    EXPECT_EQ(rtc::SrtpCryptoSuiteFromName(cs2), f2_.send_cipher_suite());
+    EXPECT_TRUE(f1_.send_key() == f2_.recv_key());
+    EXPECT_TRUE(f2_.send_key() == f1_.recv_key());
   }
-  void TestProtectUnprotect(const std::string& cs1, const std::string& cs2) {
-    Buffer rtp_buffer(sizeof(kPcmuFrame) + rtp_auth_tag_len(cs1));
-    char* rtp_packet = rtp_buffer.data<char>();
-    char original_rtp_packet[sizeof(kPcmuFrame)];
-    Buffer rtcp_buffer(sizeof(kRtcpReport) + 4 + rtcp_auth_tag_len(cs2));
-    char* rtcp_packet = rtcp_buffer.data<char>();
-    int rtp_len = sizeof(kPcmuFrame), rtcp_len = sizeof(kRtcpReport), out_len;
-    memcpy(rtp_packet, kPcmuFrame, rtp_len);
-    // In order to be able to run this test function multiple times we can not
-    // use the same sequence number twice. Increase the sequence number by one.
-    SetBE16(reinterpret_cast<uint8_t*>(rtp_packet) + 2, ++sequence_number_);
-    memcpy(original_rtp_packet, rtp_packet, rtp_len);
-    memcpy(rtcp_packet, kRtcpReport, rtcp_len);
 
-    EXPECT_TRUE(f1_.ProtectRtp(rtp_packet, rtp_len,
-                               static_cast<int>(rtp_buffer.size()),
-                               &out_len));
-    EXPECT_EQ(out_len, rtp_len + rtp_auth_tag_len(cs1));
-    EXPECT_NE(0, memcmp(rtp_packet, original_rtp_packet, rtp_len));
-    if (!f1_.IsExternalAuthActive()) {
-      EXPECT_TRUE(f2_.UnprotectRtp(rtp_packet, out_len, &out_len));
-      EXPECT_EQ(rtp_len, out_len);
-      EXPECT_EQ(0, memcmp(rtp_packet, original_rtp_packet, rtp_len));
-    } else {
-      // With external auth enabled, SRTP doesn't write the auth tag and
-      // unprotect would fail. Check accessing the information about the
-      // tag instead, similar to what the actual code would do that relies
-      // on external auth.
-      TestRtpAuthParams(&f1_, cs1);
-    }
-
-    EXPECT_TRUE(f2_.ProtectRtp(rtp_packet, rtp_len,
-                               static_cast<int>(rtp_buffer.size()),
-                               &out_len));
-    EXPECT_EQ(out_len, rtp_len + rtp_auth_tag_len(cs2));
-    EXPECT_NE(0, memcmp(rtp_packet, original_rtp_packet, rtp_len));
-    if (!f2_.IsExternalAuthActive()) {
-      EXPECT_TRUE(f1_.UnprotectRtp(rtp_packet, out_len, &out_len));
-      EXPECT_EQ(rtp_len, out_len);
-      EXPECT_EQ(0, memcmp(rtp_packet, original_rtp_packet, rtp_len));
-    } else {
-      TestRtpAuthParams(&f2_, cs2);
-    }
-
-    EXPECT_TRUE(f1_.ProtectRtcp(rtcp_packet, rtcp_len,
-                                static_cast<int>(rtcp_buffer.size()),
-                                &out_len));
-    EXPECT_EQ(out_len, rtcp_len + 4 + rtcp_auth_tag_len(cs1));  // NOLINT
-    EXPECT_NE(0, memcmp(rtcp_packet, kRtcpReport, rtcp_len));
-    EXPECT_TRUE(f2_.UnprotectRtcp(rtcp_packet, out_len, &out_len));
-    EXPECT_EQ(rtcp_len, out_len);
-    EXPECT_EQ(0, memcmp(rtcp_packet, kRtcpReport, rtcp_len));
-
-    EXPECT_TRUE(f2_.ProtectRtcp(rtcp_packet, rtcp_len,
-                                static_cast<int>(rtcp_buffer.size()),
-                                &out_len));
-    EXPECT_EQ(out_len, rtcp_len + 4 + rtcp_auth_tag_len(cs2));  // NOLINT
-    EXPECT_NE(0, memcmp(rtcp_packet, kRtcpReport, rtcp_len));
-    EXPECT_TRUE(f1_.UnprotectRtcp(rtcp_packet, out_len, &out_len));
-    EXPECT_EQ(rtcp_len, out_len);
-    EXPECT_EQ(0, memcmp(rtcp_packet, kRtcpReport, rtcp_len));
-  }
-  void TestProtectUnprotectHeaderEncryption(const std::string& cs1,
-      const std::string& cs2,
-      const std::vector<int>& encrypted_header_ids) {
-    Buffer rtp_buffer(sizeof(kPcmuFrameWithExtensions) + rtp_auth_tag_len(cs1));
-    char* rtp_packet = rtp_buffer.data<char>();
-    size_t rtp_packet_size = rtp_buffer.size();
-    char original_rtp_packet[sizeof(kPcmuFrameWithExtensions)];
-    size_t original_rtp_packet_size = sizeof(original_rtp_packet);
-    int rtp_len = sizeof(kPcmuFrameWithExtensions), out_len;
-    memcpy(rtp_packet, kPcmuFrameWithExtensions, rtp_len);
-    // In order to be able to run this test function multiple times we can not
-    // use the same sequence number twice. Increase the sequence number by one.
-    SetBE16(reinterpret_cast<uint8_t*>(rtp_packet) + 2, ++sequence_number_);
-    memcpy(original_rtp_packet, rtp_packet, rtp_len);
-
-    EXPECT_TRUE(f1_.ProtectRtp(rtp_packet, rtp_len,
-                               static_cast<int>(rtp_buffer.size()),
-                               &out_len));
-    EXPECT_EQ(out_len, rtp_len + rtp_auth_tag_len(cs1));
-    EXPECT_NE(0, memcmp(rtp_packet, original_rtp_packet, rtp_len));
-    CompareHeaderExtensions(rtp_packet, rtp_packet_size,
-        original_rtp_packet, original_rtp_packet_size,
-        encrypted_header_ids, false);
-    EXPECT_TRUE(f2_.UnprotectRtp(rtp_packet, out_len, &out_len));
-    EXPECT_EQ(rtp_len, out_len);
-    EXPECT_EQ(0, memcmp(rtp_packet, original_rtp_packet, rtp_len));
-    CompareHeaderExtensions(rtp_packet, rtp_packet_size,
-        original_rtp_packet, original_rtp_packet_size,
-        encrypted_header_ids, true);
-
-    EXPECT_TRUE(f2_.ProtectRtp(rtp_packet, rtp_len,
-                               static_cast<int>(rtp_buffer.size()),
-                               &out_len));
-    EXPECT_EQ(out_len, rtp_len + rtp_auth_tag_len(cs2));
-    EXPECT_NE(0, memcmp(rtp_packet, original_rtp_packet, rtp_len));
-    CompareHeaderExtensions(rtp_packet, rtp_packet_size,
-        original_rtp_packet, original_rtp_packet_size,
-        encrypted_header_ids, false);
-    EXPECT_TRUE(f1_.UnprotectRtp(rtp_packet, out_len, &out_len));
-    EXPECT_EQ(rtp_len, out_len);
-    EXPECT_EQ(0, memcmp(rtp_packet, original_rtp_packet, rtp_len));
-    CompareHeaderExtensions(rtp_packet, rtp_packet_size,
-        original_rtp_packet, original_rtp_packet_size,
-        encrypted_header_ids, true);
-  }
-  void TestProtectSetParamsDirect(bool enable_external_auth, int cs,
-      const uint8_t* key1, int key1_len, const uint8_t* key2, int key2_len,
-      const std::string& cs_name) {
-    EXPECT_EQ(key1_len, key2_len);
-    EXPECT_EQ(cs_name, SrtpCryptoSuiteToName(cs));
-    if (enable_external_auth) {
-      f1_.EnableExternalAuth();
-      f2_.EnableExternalAuth();
-    }
-    EXPECT_TRUE(f1_.SetRtpParams(cs, key1, key1_len, cs, key2, key2_len));
-    EXPECT_TRUE(f2_.SetRtpParams(cs, key2, key2_len, cs, key1, key1_len));
-    EXPECT_TRUE(f1_.SetRtcpParams(cs, key1, key1_len, cs, key2, key2_len));
-    EXPECT_TRUE(f2_.SetRtcpParams(cs, key2, key2_len, cs, key1, key1_len));
-    EXPECT_TRUE(f1_.IsActive());
-    EXPECT_TRUE(f2_.IsActive());
-    if (IsGcmCryptoSuite(cs)) {
-      EXPECT_FALSE(f1_.IsExternalAuthActive());
-      EXPECT_FALSE(f2_.IsExternalAuthActive());
-    } else if (enable_external_auth) {
-      EXPECT_TRUE(f1_.IsExternalAuthActive());
-      EXPECT_TRUE(f2_.IsExternalAuthActive());
-    }
-    TestProtectUnprotect(cs_name, cs_name);
-  }
-  void TestProtectSetParamsDirectHeaderEncryption(int cs,
-      const uint8_t* key1, int key1_len, const uint8_t* key2, int key2_len,
-      const std::string& cs_name) {
-    std::vector<int> encrypted_headers;
-    encrypted_headers.push_back(1);
-    // Don't encrypt header ids 2 and 3.
-    encrypted_headers.push_back(4);
-    EXPECT_EQ(key1_len, key2_len);
-    EXPECT_EQ(cs_name, SrtpCryptoSuiteToName(cs));
-    f1_.SetEncryptedHeaderExtensionIds(CS_LOCAL, encrypted_headers);
-    f1_.SetEncryptedHeaderExtensionIds(CS_REMOTE, encrypted_headers);
-    f2_.SetEncryptedHeaderExtensionIds(CS_LOCAL, encrypted_headers);
-    f2_.SetEncryptedHeaderExtensionIds(CS_REMOTE, encrypted_headers);
-    EXPECT_TRUE(f1_.SetRtpParams(cs, key1, key1_len, cs, key2, key2_len));
-    EXPECT_TRUE(f2_.SetRtpParams(cs, key2, key2_len, cs, key1, key1_len));
-    EXPECT_TRUE(f1_.IsActive());
-    EXPECT_TRUE(f2_.IsActive());
-    EXPECT_FALSE(f1_.IsExternalAuthActive());
-    EXPECT_FALSE(f2_.IsExternalAuthActive());
-    TestProtectUnprotectHeaderEncryption(cs_name, cs_name, encrypted_headers);
-  }
   cricket::SrtpFilter f1_;
   cricket::SrtpFilter f2_;
-  int sequence_number_;
 };
 
 // Test that we can set up the session and keys properly.
@@ -478,22 +293,6 @@ TEST_F(SrtpFilterTest, TestUnsupportedOptions) {
   EXPECT_FALSE(f1_.IsActive());
 }
 
-// Test that we can encrypt/decrypt after setting the same CryptoParams again on
-// one side.
-TEST_F(SrtpFilterTest, TestSettingSameKeyOnOneSide) {
-  std::vector<CryptoParams> offer(MakeVector(kTestCryptoParams1));
-  std::vector<CryptoParams> answer(MakeVector(kTestCryptoParams2));
-  TestSetParams(offer, answer);
-
-  TestProtectUnprotect(CS_AES_CM_128_HMAC_SHA1_80,
-                       CS_AES_CM_128_HMAC_SHA1_80);
-
-  // Re-applying the same keys on one end and it should not reset the ROC.
-  EXPECT_TRUE(f2_.SetOffer(offer, CS_REMOTE));
-  EXPECT_TRUE(f2_.SetAnswer(answer, CS_LOCAL));
-  TestProtectUnprotect(CS_AES_CM_128_HMAC_SHA1_80, CS_AES_CM_128_HMAC_SHA1_80);
-}
-
 // Test that we can encrypt/decrypt after negotiating AES_CM_128_HMAC_SHA1_80.
 TEST_F(SrtpFilterTest, TestProtect_AES_CM_128_HMAC_SHA1_80) {
   std::vector<CryptoParams> offer(MakeVector(kTestCryptoParams1));
@@ -502,7 +301,8 @@ TEST_F(SrtpFilterTest, TestProtect_AES_CM_128_HMAC_SHA1_80) {
   offer[1].tag = 2;
   offer[1].cipher_suite = CS_AES_CM_128_HMAC_SHA1_32;
   TestSetParams(offer, answer);
-  TestProtectUnprotect(CS_AES_CM_128_HMAC_SHA1_80, CS_AES_CM_128_HMAC_SHA1_80);
+  VerifyCryptoParamsMatch(CS_AES_CM_128_HMAC_SHA1_80,
+                          CS_AES_CM_128_HMAC_SHA1_80);
 }
 
 // Test that we can encrypt/decrypt after negotiating AES_CM_128_HMAC_SHA1_32.
@@ -515,7 +315,8 @@ TEST_F(SrtpFilterTest, TestProtect_AES_CM_128_HMAC_SHA1_32) {
   answer[0].tag = 2;
   answer[0].cipher_suite = CS_AES_CM_128_HMAC_SHA1_32;
   TestSetParams(offer, answer);
-  TestProtectUnprotect(CS_AES_CM_128_HMAC_SHA1_32, CS_AES_CM_128_HMAC_SHA1_32);
+  VerifyCryptoParamsMatch(CS_AES_CM_128_HMAC_SHA1_32,
+                          CS_AES_CM_128_HMAC_SHA1_32);
 }
 
 // Test that we can change encryption parameters.
@@ -524,7 +325,8 @@ TEST_F(SrtpFilterTest, TestChangeParameters) {
   std::vector<CryptoParams> answer(MakeVector(kTestCryptoParams2));
 
   TestSetParams(offer, answer);
-  TestProtectUnprotect(CS_AES_CM_128_HMAC_SHA1_80, CS_AES_CM_128_HMAC_SHA1_80);
+  VerifyCryptoParamsMatch(CS_AES_CM_128_HMAC_SHA1_80,
+                          CS_AES_CM_128_HMAC_SHA1_80);
 
   // Change the key parameters and cipher_suite.
   offer[0].key_params = kTestKeyParams3;
@@ -538,13 +340,15 @@ TEST_F(SrtpFilterTest, TestChangeParameters) {
   EXPECT_TRUE(f1_.IsActive());
 
   // Test that the old keys are valid until the negotiation is complete.
-  TestProtectUnprotect(CS_AES_CM_128_HMAC_SHA1_80, CS_AES_CM_128_HMAC_SHA1_80);
+  VerifyCryptoParamsMatch(CS_AES_CM_128_HMAC_SHA1_80,
+                          CS_AES_CM_128_HMAC_SHA1_80);
 
   // Complete the negotiation and test that we can still understand each other.
   EXPECT_TRUE(f2_.SetAnswer(answer, CS_LOCAL));
   EXPECT_TRUE(f1_.SetAnswer(answer, CS_REMOTE));
 
-  TestProtectUnprotect(CS_AES_CM_128_HMAC_SHA1_32, CS_AES_CM_128_HMAC_SHA1_32);
+  VerifyCryptoParamsMatch(CS_AES_CM_128_HMAC_SHA1_32,
+                          CS_AES_CM_128_HMAC_SHA1_32);
 }
 
 // Test that we can send and receive provisional answers with crypto enabled.
@@ -564,7 +368,8 @@ TEST_F(SrtpFilterTest, TestProvisionalAnswer) {
   EXPECT_TRUE(f1_.SetProvisionalAnswer(answer, CS_REMOTE));
   EXPECT_TRUE(f1_.IsActive());
   EXPECT_TRUE(f2_.IsActive());
-  TestProtectUnprotect(CS_AES_CM_128_HMAC_SHA1_80, CS_AES_CM_128_HMAC_SHA1_80);
+  VerifyCryptoParamsMatch(CS_AES_CM_128_HMAC_SHA1_80,
+                          CS_AES_CM_128_HMAC_SHA1_80);
 
   answer[0].key_params = kTestKeyParams4;
   answer[0].tag = 2;
@@ -573,7 +378,8 @@ TEST_F(SrtpFilterTest, TestProvisionalAnswer) {
   EXPECT_TRUE(f1_.SetAnswer(answer, CS_REMOTE));
   EXPECT_TRUE(f1_.IsActive());
   EXPECT_TRUE(f2_.IsActive());
-  TestProtectUnprotect(CS_AES_CM_128_HMAC_SHA1_32, CS_AES_CM_128_HMAC_SHA1_32);
+  VerifyCryptoParamsMatch(CS_AES_CM_128_HMAC_SHA1_32,
+                          CS_AES_CM_128_HMAC_SHA1_32);
 }
 
 // Test that a provisional answer doesn't need to contain a crypto.
@@ -595,7 +401,8 @@ TEST_F(SrtpFilterTest, TestProvisionalAnswerWithoutCrypto) {
   EXPECT_TRUE(f1_.SetAnswer(answer, CS_REMOTE));
   EXPECT_TRUE(f1_.IsActive());
   EXPECT_TRUE(f2_.IsActive());
-  TestProtectUnprotect(CS_AES_CM_128_HMAC_SHA1_80, CS_AES_CM_128_HMAC_SHA1_80);
+  VerifyCryptoParamsMatch(CS_AES_CM_128_HMAC_SHA1_80,
+                          CS_AES_CM_128_HMAC_SHA1_80);
 }
 
 // Test that if we get a new local offer after a provisional answer
@@ -622,7 +429,8 @@ TEST_F(SrtpFilterTest, TestLocalOfferAfterProvisionalAnswerWithoutCrypto) {
   EXPECT_TRUE(f1_.SetAnswer(answer, CS_REMOTE));
   EXPECT_TRUE(f1_.IsActive());
   EXPECT_TRUE(f2_.IsActive());
-  TestProtectUnprotect(CS_AES_CM_128_HMAC_SHA1_80, CS_AES_CM_128_HMAC_SHA1_80);
+  VerifyCryptoParamsMatch(CS_AES_CM_128_HMAC_SHA1_80,
+                          CS_AES_CM_128_HMAC_SHA1_80);
 }
 
 // Test that we can disable encryption.
@@ -631,7 +439,8 @@ TEST_F(SrtpFilterTest, TestDisableEncryption) {
   std::vector<CryptoParams> answer(MakeVector(kTestCryptoParams2));
 
   TestSetParams(offer, answer);
-  TestProtectUnprotect(CS_AES_CM_128_HMAC_SHA1_80, CS_AES_CM_128_HMAC_SHA1_80);
+  VerifyCryptoParamsMatch(CS_AES_CM_128_HMAC_SHA1_80,
+                          CS_AES_CM_128_HMAC_SHA1_80);
 
   offer.clear();
   answer.clear();
@@ -641,7 +450,8 @@ TEST_F(SrtpFilterTest, TestDisableEncryption) {
   EXPECT_TRUE(f2_.IsActive());
 
   // Test that the old keys are valid until the negotiation is complete.
-  TestProtectUnprotect(CS_AES_CM_128_HMAC_SHA1_80, CS_AES_CM_128_HMAC_SHA1_80);
+  VerifyCryptoParamsMatch(CS_AES_CM_128_HMAC_SHA1_80,
+                          CS_AES_CM_128_HMAC_SHA1_80);
 
   // Complete the negotiation.
   EXPECT_TRUE(f2_.SetAnswer(answer, CS_LOCAL));
@@ -651,86 +461,4 @@ TEST_F(SrtpFilterTest, TestDisableEncryption) {
   EXPECT_FALSE(f2_.IsActive());
 }
 
-class SrtpFilterProtectSetParamsDirectTest
-  : public SrtpFilterTest,
-    public testing::WithParamInterface<bool> {
-};
-
-// Test directly setting the params with AES_CM_128_HMAC_SHA1_80.
-TEST_P(SrtpFilterProtectSetParamsDirectTest, Test_AES_CM_128_HMAC_SHA1_80) {
-  bool enable_external_auth = GetParam();
-  TestProtectSetParamsDirect(enable_external_auth, SRTP_AES128_CM_SHA1_80,
-                             kTestKey1, kTestKeyLen, kTestKey2, kTestKeyLen,
-                             CS_AES_CM_128_HMAC_SHA1_80);
-}
-
-TEST_F(SrtpFilterTest,
-    TestProtectSetParamsDirectHeaderEncryption_AES_CM_128_HMAC_SHA1_80) {
-  TestProtectSetParamsDirectHeaderEncryption(
-      SRTP_AES128_CM_SHA1_80, kTestKey1, kTestKeyLen, kTestKey2, kTestKeyLen,
-      CS_AES_CM_128_HMAC_SHA1_80);
-}
-
-// Test directly setting the params with AES_CM_128_HMAC_SHA1_32.
-TEST_P(SrtpFilterProtectSetParamsDirectTest, Test_AES_CM_128_HMAC_SHA1_32) {
-  bool enable_external_auth = GetParam();
-  TestProtectSetParamsDirect(enable_external_auth, SRTP_AES128_CM_SHA1_32,
-                             kTestKey1, kTestKeyLen, kTestKey2, kTestKeyLen,
-                             CS_AES_CM_128_HMAC_SHA1_32);
-}
-
-TEST_F(SrtpFilterTest,
-    TestProtectSetParamsDirectHeaderEncryption_AES_CM_128_HMAC_SHA1_32) {
-  TestProtectSetParamsDirectHeaderEncryption(
-      SRTP_AES128_CM_SHA1_32, kTestKey1, kTestKeyLen, kTestKey2, kTestKeyLen,
-      CS_AES_CM_128_HMAC_SHA1_32);
-}
-
-// Test directly setting the params with SRTP_AEAD_AES_128_GCM.
-TEST_P(SrtpFilterProtectSetParamsDirectTest, Test_SRTP_AEAD_AES_128_GCM) {
-  bool enable_external_auth = GetParam();
-  TestProtectSetParamsDirect(enable_external_auth, SRTP_AEAD_AES_128_GCM,
-                             kTestKeyGcm128_1, kTestKeyGcm128Len,
-                             kTestKeyGcm128_2, kTestKeyGcm128Len,
-                             CS_AEAD_AES_128_GCM);
-}
-
-TEST_F(SrtpFilterTest,
-    TestProtectSetParamsDirectHeaderEncryption_SRTP_AEAD_AES_128_GCM) {
-  TestProtectSetParamsDirectHeaderEncryption(
-      SRTP_AEAD_AES_128_GCM, kTestKeyGcm128_1, kTestKeyGcm128Len,
-      kTestKeyGcm128_2, kTestKeyGcm128Len, CS_AEAD_AES_128_GCM);
-}
-
-// Test directly setting the params with SRTP_AEAD_AES_256_GCM.
-TEST_P(SrtpFilterProtectSetParamsDirectTest, Test_SRTP_AEAD_AES_256_GCM) {
-  bool enable_external_auth = GetParam();
-  TestProtectSetParamsDirect(enable_external_auth, SRTP_AEAD_AES_256_GCM,
-                             kTestKeyGcm256_1, kTestKeyGcm256Len,
-                             kTestKeyGcm256_2, kTestKeyGcm256Len,
-                             CS_AEAD_AES_256_GCM);
-}
-
-TEST_F(SrtpFilterTest,
-    TestProtectSetParamsDirectHeaderEncryption_SRTP_AEAD_AES_256_GCM) {
-  TestProtectSetParamsDirectHeaderEncryption(
-      SRTP_AEAD_AES_256_GCM, kTestKeyGcm256_1, kTestKeyGcm256Len,
-      kTestKeyGcm256_2, kTestKeyGcm256Len, CS_AEAD_AES_256_GCM);
-}
-
-// Run all tests both with and without external auth enabled.
-INSTANTIATE_TEST_CASE_P(ExternalAuth,
-                        SrtpFilterProtectSetParamsDirectTest,
-                        ::testing::Values(true, false));
-
-// Test directly setting the params with bogus keys.
-TEST_F(SrtpFilterTest, TestSetParamsKeyTooShort) {
-  EXPECT_FALSE(f1_.SetRtpParams(SRTP_AES128_CM_SHA1_80, kTestKey1,
-                                kTestKeyLen - 1, SRTP_AES128_CM_SHA1_80,
-                                kTestKey1, kTestKeyLen - 1));
-  EXPECT_FALSE(f1_.SetRtcpParams(SRTP_AES128_CM_SHA1_80, kTestKey1,
-                                 kTestKeyLen - 1, SRTP_AES128_CM_SHA1_80,
-                                 kTestKey1, kTestKeyLen - 1));
-}
-
 }  // namespace rtc
diff --git a/webrtc/pc/srtptransport.cc b/webrtc/pc/srtptransport.cc
index 6e6ff06274..d9f054be7e 100644
--- a/webrtc/pc/srtptransport.cc
+++ b/webrtc/pc/srtptransport.cc
@@ -16,6 +16,7 @@
 #include "webrtc/pc/rtptransport.h"
 #include "webrtc/pc/srtpsession.h"
 #include "webrtc/rtc_base/asyncpacketsocket.h"
+#include "webrtc/rtc_base/base64.h"
 #include "webrtc/rtc_base/copyonwritebuffer.h"
 #include "webrtc/rtc_base/ptr_util.h"
 #include "webrtc/rtc_base/trace_event.h"
@@ -42,21 +43,322 @@ void SrtpTransport::ConnectToRtpTransport() {
                                             &SrtpTransport::OnReadyToSend);
 }
 
+bool SrtpTransport::SendRtpPacket(rtc::CopyOnWriteBuffer* packet,
+                                  const rtc::PacketOptions& options,
+                                  int flags) {
+  return SendPacket(false, packet, options, flags);
+}
+
+bool SrtpTransport::SendRtcpPacket(rtc::CopyOnWriteBuffer* packet,
+                                   const rtc::PacketOptions& options,
+                                   int flags) {
+  return SendPacket(true, packet, options, flags);
+}
+
 bool SrtpTransport::SendPacket(bool rtcp,
                                rtc::CopyOnWriteBuffer* packet,
                                const rtc::PacketOptions& options,
                                int flags) {
-  // TODO(zstein): Protect packet.
+  if (!IsActive()) {
+    LOG(LS_ERROR)
+        << "Failed to send the packet because SRTP transport is inactive.";
+    return false;
+  }
 
-  return rtp_transport_->SendPacket(rtcp, packet, options, flags);
+  rtc::PacketOptions updated_options = options;
+  rtc::CopyOnWriteBuffer cp = *packet;
+  TRACE_EVENT0("webrtc", "SRTP Encode");
+  bool res;
+  uint8_t* data = packet->data();
+  int len = static_cast<int>(packet->size());
+  if (!rtcp) {
+// If ENABLE_EXTERNAL_AUTH flag is on then packet authentication is not done
+// inside libsrtp for a RTP packet. A external HMAC module will be writing
+// a fake HMAC value. This is ONLY done for a RTP packet.
+// Socket layer will update rtp sendtime extension header if present in
+// packet with current time before updating the HMAC.
+#if !defined(ENABLE_EXTERNAL_AUTH)
+    res = ProtectRtp(data, len, static_cast<int>(packet->capacity()), &len);
+#else
+    if (!IsExternalAuthActive()) {
+      res = ProtectRtp(data, len, static_cast<int>(packet->capacity()), &len);
+    } else {
+      updated_options.packet_time_params.rtp_sendtime_extension_id =
+          rtp_abs_sendtime_extn_id_;
+      res = ProtectRtp(data, len, static_cast<int>(packet->capacity()), &len,
+                       &updated_options.packet_time_params.srtp_packet_index);
+      // If protection succeeds, let's get auth params from srtp.
+      if (res) {
+        uint8_t* auth_key = NULL;
+        int key_len;
+        res = GetRtpAuthParams(
+            &auth_key, &key_len,
+            &updated_options.packet_time_params.srtp_auth_tag_len);
+        if (res) {
+          updated_options.packet_time_params.srtp_auth_key.resize(key_len);
+          updated_options.packet_time_params.srtp_auth_key.assign(
+              auth_key, auth_key + key_len);
+        }
+      }
+    }
+#endif
+    if (!res) {
+      int seq_num = -1;
+      uint32_t ssrc = 0;
+      cricket::GetRtpSeqNum(data, len, &seq_num);
+      cricket::GetRtpSsrc(data, len, &ssrc);
+      LOG(LS_ERROR) << "Failed to protect " << content_name_
+                    << " RTP packet: size=" << len << ", seqnum=" << seq_num
+                    << ", SSRC=" << ssrc;
+      return false;
+    }
+  } else {
+    res = ProtectRtcp(data, len, static_cast<int>(packet->capacity()), &len);
+    if (!res) {
+      int type = -1;
+      cricket::GetRtcpType(data, len, &type);
+      LOG(LS_ERROR) << "Failed to protect " << content_name_
+                    << " RTCP packet: size=" << len << ", type=" << type;
+      return false;
+    }
+  }
+
+  // Update the length of the packet now that we've added the auth tag.
+  packet->SetSize(len);
+  return rtcp ? rtp_transport_->SendRtcpPacket(packet, updated_options, flags)
+              : rtp_transport_->SendRtpPacket(packet, updated_options, flags);
 }
 
 void SrtpTransport::OnPacketReceived(bool rtcp,
                                      rtc::CopyOnWriteBuffer* packet,
                                      const rtc::PacketTime& packet_time) {
-  // TODO(zstein): Unprotect packet.
+  if (!IsActive()) {
+    LOG(LS_WARNING) << "Inactive SRTP transport received a packet. Drop it.";
+    return;
+  }
 
+  TRACE_EVENT0("webrtc", "SRTP Decode");
+  char* data = packet->data<char>();
+  int len = static_cast<int>(packet->size());
+  bool res;
+  if (!rtcp) {
+    res = UnprotectRtp(data, len, &len);
+    if (!res) {
+      int seq_num = -1;
+      uint32_t ssrc = 0;
+      cricket::GetRtpSeqNum(data, len, &seq_num);
+      cricket::GetRtpSsrc(data, len, &ssrc);
+      LOG(LS_ERROR) << "Failed to unprotect " << content_name_
+                    << " RTP packet: size=" << len << ", seqnum=" << seq_num
+                    << ", SSRC=" << ssrc;
+      return;
+    }
+  } else {
+    res = UnprotectRtcp(data, len, &len);
+    if (!res) {
+      int type = -1;
+      cricket::GetRtcpType(data, len, &type);
+      LOG(LS_ERROR) << "Failed to unprotect " << content_name_
+                    << " RTCP packet: size=" << len << ", type=" << type;
+      return;
+    }
+  }
+
+  packet->SetSize(len);
   SignalPacketReceived(rtcp, packet, packet_time);
 }
 
+bool SrtpTransport::SetRtpParams(int send_cs,
+                                 const uint8_t* send_key,
+                                 int send_key_len,
+                                 int recv_cs,
+                                 const uint8_t* recv_key,
+                                 int recv_key_len) {
+  CreateSrtpSessions();
+  send_session_->SetEncryptedHeaderExtensionIds(
+      send_encrypted_header_extension_ids_);
+  if (external_auth_enabled_) {
+    send_session_->EnableExternalAuth();
+  }
+  if (!send_session_->SetSend(send_cs, send_key, send_key_len)) {
+    ResetParams();
+    return false;
+  }
+
+  recv_session_->SetEncryptedHeaderExtensionIds(
+      recv_encrypted_header_extension_ids_);
+  if (!recv_session_->SetRecv(recv_cs, recv_key, recv_key_len)) {
+    ResetParams();
+    return false;
+  }
+
+  LOG(LS_INFO) << "SRTP activated with negotiated parameters:"
+               << " send cipher_suite " << send_cs << " recv cipher_suite "
+               << recv_cs;
+  return true;
+}
+
+bool SrtpTransport::SetRtcpParams(int send_cs,
+                                  const uint8_t* send_key,
+                                  int send_key_len,
+                                  int recv_cs,
+                                  const uint8_t* recv_key,
+                                  int recv_key_len) {
+  // This can only be called once, but can be safely called after
+  // SetRtpParams
+  if (send_rtcp_session_ || recv_rtcp_session_) {
+    LOG(LS_ERROR) << "Tried to set SRTCP Params when filter already active";
+    return false;
+  }
+
+  send_rtcp_session_.reset(new cricket::SrtpSession());
+  if (!send_rtcp_session_->SetRecv(send_cs, send_key, send_key_len)) {
+    return false;
+  }
+
+  recv_rtcp_session_.reset(new cricket::SrtpSession());
+  if (!recv_rtcp_session_->SetRecv(recv_cs, recv_key, recv_key_len)) {
+    return false;
+  }
+
+  LOG(LS_INFO) << "SRTCP activated with negotiated parameters:"
+               << " send cipher_suite " << send_cs << " recv cipher_suite "
+               << recv_cs;
+
+  return true;
+}
+
+bool SrtpTransport::IsActive() const {
+  return send_session_ && recv_session_;
+}
+
+void SrtpTransport::ResetParams() {
+  send_session_ = nullptr;
+  recv_session_ = nullptr;
+  send_rtcp_session_ = nullptr;
+  recv_rtcp_session_ = nullptr;
+  LOG(LS_INFO) << "The params in SRTP transport are reset.";
+}
+
+void SrtpTransport::SetEncryptedHeaderExtensionIds(
+    cricket::ContentSource source,
+    const std::vector<int>& extension_ids) {
+  if (source == cricket::CS_LOCAL) {
+    recv_encrypted_header_extension_ids_ = extension_ids;
+  } else {
+    send_encrypted_header_extension_ids_ = extension_ids;
+  }
+}
+
+void SrtpTransport::CreateSrtpSessions() {
+  send_session_.reset(new cricket::SrtpSession());
+  recv_session_.reset(new cricket::SrtpSession());
+
+  if (external_auth_enabled_) {
+    send_session_->EnableExternalAuth();
+  }
+}
+
+bool SrtpTransport::ProtectRtp(void* p, int in_len, int max_len, int* out_len) {
+  if (!IsActive()) {
+    LOG(LS_WARNING) << "Failed to ProtectRtp: SRTP not active";
+    return false;
+  }
+  RTC_CHECK(send_session_);
+  return send_session_->ProtectRtp(p, in_len, max_len, out_len);
+}
+
+bool SrtpTransport::ProtectRtp(void* p,
+                               int in_len,
+                               int max_len,
+                               int* out_len,
+                               int64_t* index) {
+  if (!IsActive()) {
+    LOG(LS_WARNING) << "Failed to ProtectRtp: SRTP not active";
+    return false;
+  }
+  RTC_CHECK(send_session_);
+  return send_session_->ProtectRtp(p, in_len, max_len, out_len, index);
+}
+
+bool SrtpTransport::ProtectRtcp(void* p,
+                                int in_len,
+                                int max_len,
+                                int* out_len) {
+  if (!IsActive()) {
+    LOG(LS_WARNING) << "Failed to ProtectRtcp: SRTP not active";
+    return false;
+  }
+  if (send_rtcp_session_) {
+    return send_rtcp_session_->ProtectRtcp(p, in_len, max_len, out_len);
+  } else {
+    RTC_CHECK(send_session_);
+    return send_session_->ProtectRtcp(p, in_len, max_len, out_len);
+  }
+}
+
+bool SrtpTransport::UnprotectRtp(void* p, int in_len, int* out_len) {
+  if (!IsActive()) {
+    LOG(LS_WARNING) << "Failed to UnprotectRtp: SRTP not active";
+    return false;
+  }
+  RTC_CHECK(recv_session_);
+  return recv_session_->UnprotectRtp(p, in_len, out_len);
+}
+
+bool SrtpTransport::UnprotectRtcp(void* p, int in_len, int* out_len) {
+  if (!IsActive()) {
+    LOG(LS_WARNING) << "Failed to UnprotectRtcp: SRTP not active";
+    return false;
+  }
+  if (recv_rtcp_session_) {
+    return recv_rtcp_session_->UnprotectRtcp(p, in_len, out_len);
+  } else {
+    RTC_CHECK(recv_session_);
+    return recv_session_->UnprotectRtcp(p, in_len, out_len);
+  }
+}
+
+bool SrtpTransport::GetRtpAuthParams(uint8_t** key,
+                                     int* key_len,
+                                     int* tag_len) {
+  if (!IsActive()) {
+    LOG(LS_WARNING) << "Failed to GetRtpAuthParams: SRTP not active";
+    return false;
+  }
+
+  RTC_CHECK(send_session_);
+  return send_session_->GetRtpAuthParams(key, key_len, tag_len);
+}
+
+bool SrtpTransport::GetSrtpOverhead(int* srtp_overhead) const {
+  if (!IsActive()) {
+    LOG(LS_WARNING) << "Failed to GetSrtpOverhead: SRTP not active";
+    return false;
+  }
+
+  RTC_CHECK(send_session_);
+  *srtp_overhead = send_session_->GetSrtpOverhead();
+  return true;
+}
+
+void SrtpTransport::EnableExternalAuth() {
+  RTC_DCHECK(!IsActive());
+  external_auth_enabled_ = true;
+}
+
+bool SrtpTransport::IsExternalAuthEnabled() const {
+  return external_auth_enabled_;
+}
+
+bool SrtpTransport::IsExternalAuthActive() const {
+  if (!IsActive()) {
+    LOG(LS_WARNING) << "Failed to check IsExternalAuthActive: SRTP not active";
+    return false;
+  }
+
+  RTC_CHECK(send_session_);
+  return send_session_->IsExternalAuthActive();
+}
+
 }  // namespace webrtc
diff --git a/webrtc/pc/srtptransport.h b/webrtc/pc/srtptransport.h
index 58ef205f87..769df0620a 100644
--- a/webrtc/pc/srtptransport.h
+++ b/webrtc/pc/srtptransport.h
@@ -17,20 +17,17 @@
 
 #include "webrtc/pc/rtptransportinternal.h"
 #include "webrtc/pc/srtpfilter.h"
+#include "webrtc/pc/srtpsession.h"
 #include "webrtc/rtc_base/checks.h"
 
 namespace webrtc {
 
 // This class will eventually be a wrapper around RtpTransportInternal
-// that protects and unprotects sent and received RTP packets. This
-// functionality is currently implemented by SrtpFilter and BaseChannel, but
-// will be moved here in the future.
+// that protects and unprotects sent and received RTP packets.
 class SrtpTransport : public RtpTransportInternal {
  public:
   SrtpTransport(bool rtcp_mux_enabled, const std::string& content_name);
 
-  // TODO(zstein): Consider taking an RtpTransport instead of an
-  // RtpTransportInternal.
   SrtpTransport(std::unique_ptr<RtpTransportInternal> transport,
                 const std::string& content_name);
 
@@ -61,14 +58,21 @@ class SrtpTransport : public RtpTransportInternal {
     return rtp_transport_->GetRtcpPacketTransport();
   }
 
+  bool SendRtpPacket(rtc::CopyOnWriteBuffer* packet,
+                     const rtc::PacketOptions& options,
+                     int flags) override;
+
+  bool SendRtcpPacket(rtc::CopyOnWriteBuffer* packet,
+                      const rtc::PacketOptions& options,
+                      int flags) override;
+
   bool IsWritable(bool rtcp) const override {
     return rtp_transport_->IsWritable(rtcp);
   }
 
-  bool SendPacket(bool rtcp,
-                  rtc::CopyOnWriteBuffer* packet,
-                  const rtc::PacketOptions& options,
-                  int flags) override;
+  // The transport becomes active if the send_session_ and recv_session_ are
+  // created.
+  bool IsActive() const;
 
   bool HandlesPayloadType(int payload_type) const override {
     return rtp_transport_->HandlesPayloadType(payload_type);
@@ -89,18 +93,104 @@ class SrtpTransport : public RtpTransportInternal {
   // TODO(zstein): Remove this when we remove RtpTransportAdapter.
   RtpTransportAdapter* GetInternal() override { return nullptr; }
 
+  // Create new send/recv sessions and set the negotiated crypto keys for RTP
+  // packet encryption. The keys can either come from SDES negotiation or DTLS
+  // handshake.
+  bool SetRtpParams(int send_cs,
+                    const uint8_t* send_key,
+                    int send_key_len,
+                    int recv_cs,
+                    const uint8_t* recv_key,
+                    int recv_key_len);
+
+  // Create new send/recv sessions and set the negotiated crypto keys for RTCP
+  // packet encryption. The keys can either come from SDES negotiation or DTLS
+  // handshake.
+  bool SetRtcpParams(int send_cs,
+                     const uint8_t* send_key,
+                     int send_key_len,
+                     int recv_cs,
+                     const uint8_t* recv_key,
+                     int recv_key_len);
+
+  void ResetParams();
+
+  // Set the header extension ids that should be encrypted for the given source.
+  // This method doesn't immediately update the SRTP session with the new IDs,
+  // and you need to call SetRtpParams for that to happen.
+  void SetEncryptedHeaderExtensionIds(cricket::ContentSource source,
+                                      const std::vector<int>& extension_ids);
+
+  // If external auth is enabled, SRTP will write a dummy auth tag that then
+  // later must get replaced before the packet is sent out. Only supported for
+  // non-GCM cipher suites and can be checked through "IsExternalAuthActive"
+  // if it is actually used. This method is only valid before the RTP params
+  // have been set.
+  void EnableExternalAuth();
+  bool IsExternalAuthEnabled() const;
+
+  // A SrtpTransport supports external creation of the auth tag if a non-GCM
+  // cipher is used. This method is only valid after the RTP params have
+  // been set.
+  bool IsExternalAuthActive() const;
+
+  // Returns srtp overhead for rtp packets.
+  bool GetSrtpOverhead(int* srtp_overhead) const;
+
+  // Returns rtp auth params from srtp context.
+  bool GetRtpAuthParams(uint8_t** key, int* key_len, int* tag_len);
+
+  // Helper method to get RTP Absoulute SendTime extension header id if
+  // present in remote supported extensions list.
+  void CacheRtpAbsSendTimeHeaderExtension(int rtp_abs_sendtime_extn_id) {
+    rtp_abs_sendtime_extn_id_ = rtp_abs_sendtime_extn_id;
+  }
+
  private:
+  void CreateSrtpSessions();
+
   void ConnectToRtpTransport();
 
+  bool SendPacket(bool rtcp,
+                  rtc::CopyOnWriteBuffer* packet,
+                  const rtc::PacketOptions& options,
+                  int flags);
+
   void OnPacketReceived(bool rtcp,
                         rtc::CopyOnWriteBuffer* packet,
                         const rtc::PacketTime& packet_time);
 
   void OnReadyToSend(bool ready) { SignalReadyToSend(ready); }
 
-  const std::string content_name_;
+  bool ProtectRtp(void* data, int in_len, int max_len, int* out_len);
 
+  // Overloaded version, outputs packet index.
+  bool ProtectRtp(void* data,
+                  int in_len,
+                  int max_len,
+                  int* out_len,
+                  int64_t* index);
+  bool ProtectRtcp(void* data, int in_len, int max_len, int* out_len);
+
+  // Decrypts/verifies an invidiual RTP/RTCP packet.
+  // If an HMAC is used, this will decrease the packet size.
+  bool UnprotectRtp(void* data, int in_len, int* out_len);
+
+  bool UnprotectRtcp(void* data, int in_len, int* out_len);
+
+  const std::string content_name_;
   std::unique_ptr<RtpTransportInternal> rtp_transport_;
+
+  std::unique_ptr<cricket::SrtpSession> send_session_;
+  std::unique_ptr<cricket::SrtpSession> recv_session_;
+  std::unique_ptr<cricket::SrtpSession> send_rtcp_session_;
+  std::unique_ptr<cricket::SrtpSession> recv_rtcp_session_;
+
+  std::vector<int> send_encrypted_header_extension_ids_;
+  std::vector<int> recv_encrypted_header_extension_ids_;
+  bool external_auth_enabled_ = false;
+
+  int rtp_abs_sendtime_extn_id_ = -1;
 };
 
 }  // namespace webrtc
diff --git a/webrtc/pc/srtptransport_unittest.cc b/webrtc/pc/srtptransport_unittest.cc
index e54dac3ea2..e097ff17cd 100644
--- a/webrtc/pc/srtptransport_unittest.cc
+++ b/webrtc/pc/srtptransport_unittest.cc
@@ -10,67 +10,413 @@
 
 #include "webrtc/pc/srtptransport.h"
 
+#include "webrtc/media/base/fakertp.h"
+#include "webrtc/p2p/base/dtlstransportinternal.h"
+#include "webrtc/p2p/base/fakepackettransport.h"
 #include "webrtc/pc/rtptransport.h"
 #include "webrtc/pc/rtptransporttestutil.h"
+#include "webrtc/pc/srtptestutil.h"
 #include "webrtc/rtc_base/asyncpacketsocket.h"
 #include "webrtc/rtc_base/gunit.h"
 #include "webrtc/rtc_base/ptr_util.h"
-#include "webrtc/test/gmock.h"
+#include "webrtc/rtc_base/sslstreamadapter.h"
+
+using rtc::kTestKey1;
+using rtc::kTestKey2;
+using rtc::kTestKeyLen;
+using rtc::SRTP_AEAD_AES_128_GCM;
 
 namespace webrtc {
+static const uint8_t kTestKeyGcm128_1[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ12";
+static const uint8_t kTestKeyGcm128_2[] = "21ZYXWVUTSRQPONMLKJIHGFEDCBA";
+static const int kTestKeyGcm128Len = 28;  // 128 bits key + 96 bits salt.
+static const uint8_t kTestKeyGcm256_1[] =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqr";
+static const uint8_t kTestKeyGcm256_2[] =
+    "rqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA";
+static const int kTestKeyGcm256Len = 44;  // 256 bits key + 96 bits salt.
 
-using testing::_;
-using testing::Return;
+class SrtpTransportTest : public testing::Test, public sigslot::has_slots<> {
+ protected:
+  SrtpTransportTest() {
+    bool rtcp_mux_enabled = true;
+    auto rtp_transport1 = rtc::MakeUnique<RtpTransport>(rtcp_mux_enabled);
+    auto rtp_transport2 = rtc::MakeUnique<RtpTransport>(rtcp_mux_enabled);
 
-class MockRtpTransport : public RtpTransport {
- public:
-  MockRtpTransport() : RtpTransport(true) {}
+    rtp_packet_transport1_ =
+        rtc::MakeUnique<rtc::FakePacketTransport>("fake_packet_transport1");
+    rtp_packet_transport2_ =
+        rtc::MakeUnique<rtc::FakePacketTransport>("fake_packet_transport2");
 
-  MOCK_METHOD4(SendPacket,
-               bool(bool rtcp,
-                    rtc::CopyOnWriteBuffer* packet,
-                    const rtc::PacketOptions& options,
-                    int flags));
+    bool asymmetric = false;
+    rtp_packet_transport1_->SetDestination(rtp_packet_transport2_.get(),
+                                           asymmetric);
 
-  void PretendReceivedPacket() {
-    bool rtcp = false;
-    rtc::CopyOnWriteBuffer buffer;
-    rtc::PacketTime time;
-    SignalPacketReceived(rtcp, &buffer, time);
+    rtp_transport1->SetRtpPacketTransport(rtp_packet_transport1_.get());
+    rtp_transport2->SetRtpPacketTransport(rtp_packet_transport2_.get());
+
+    // Add payload type for RTP packet and RTCP packet.
+    rtp_transport1->AddHandledPayloadType(0x00);
+    rtp_transport2->AddHandledPayloadType(0x00);
+    rtp_transport1->AddHandledPayloadType(0xc9);
+    rtp_transport2->AddHandledPayloadType(0xc9);
+
+    srtp_transport1_ =
+        rtc::MakeUnique<SrtpTransport>(std::move(rtp_transport1), "content");
+    srtp_transport2_ =
+        rtc::MakeUnique<SrtpTransport>(std::move(rtp_transport2), "content");
+
+    srtp_transport1_->SignalPacketReceived.connect(
+        this, &SrtpTransportTest::OnPacketReceived1);
+    srtp_transport2_->SignalPacketReceived.connect(
+        this, &SrtpTransportTest::OnPacketReceived2);
   }
+
+  void OnPacketReceived1(bool rtcp,
+                         rtc::CopyOnWriteBuffer* packet,
+                         const rtc::PacketTime& packet_time) {
+    LOG(LS_INFO) << "SrtpTransport1 Received a packet.";
+    last_recv_packet1_ = *packet;
+  }
+
+  void OnPacketReceived2(bool rtcp,
+                         rtc::CopyOnWriteBuffer* packet,
+                         const rtc::PacketTime& packet_time) {
+    LOG(LS_INFO) << "SrtpTransport2 Received a packet.";
+    last_recv_packet2_ = *packet;
+  }
+
+  // With external auth enabled, SRTP doesn't write the auth tag and
+  // unprotect would fail. Check accessing the information about the
+  // tag instead, similar to what the actual code would do that relies
+  // on external auth.
+  void TestRtpAuthParams(SrtpTransport* transport, const std::string& cs) {
+    int overhead;
+    EXPECT_TRUE(transport->GetSrtpOverhead(&overhead));
+    switch (rtc::SrtpCryptoSuiteFromName(cs)) {
+      case rtc::SRTP_AES128_CM_SHA1_32:
+        EXPECT_EQ(32 / 8, overhead);  // 32-bit tag.
+        break;
+      case rtc::SRTP_AES128_CM_SHA1_80:
+        EXPECT_EQ(80 / 8, overhead);  // 80-bit tag.
+        break;
+      default:
+        RTC_NOTREACHED();
+        break;
+    }
+
+    uint8_t* auth_key = nullptr;
+    int key_len = 0;
+    int tag_len = 0;
+    EXPECT_TRUE(transport->GetRtpAuthParams(&auth_key, &key_len, &tag_len));
+    EXPECT_NE(nullptr, auth_key);
+    EXPECT_EQ(160 / 8, key_len);  // Length of SHA-1 is 160 bits.
+    EXPECT_EQ(overhead, tag_len);
+  }
+
+  void TestSendRecvRtpPacket(const std::string& cipher_suite_name) {
+    size_t rtp_len = sizeof(kPcmuFrame);
+    size_t packet_size = rtp_len + rtc::rtp_auth_tag_len(cipher_suite_name);
+    rtc::Buffer rtp_packet_buffer(packet_size);
+    char* rtp_packet_data = rtp_packet_buffer.data<char>();
+    memcpy(rtp_packet_data, kPcmuFrame, rtp_len);
+    // In order to be able to run this test function multiple times we can not
+    // use the same sequence number twice. Increase the sequence number by one.
+    rtc::SetBE16(reinterpret_cast<uint8_t*>(rtp_packet_data) + 2,
+                 ++sequence_number_);
+    rtc::CopyOnWriteBuffer rtp_packet1to2(rtp_packet_data, rtp_len,
+                                          packet_size);
+    rtc::CopyOnWriteBuffer rtp_packet2to1(rtp_packet_data, rtp_len,
+                                          packet_size);
+
+    char original_rtp_data[sizeof(kPcmuFrame)];
+    memcpy(original_rtp_data, rtp_packet_data, rtp_len);
+
+    rtc::PacketOptions options;
+    // Send a packet from |srtp_transport1_| to |srtp_transport2_| and verify
+    // that the packet can be successfully received and decrypted.
+    ASSERT_TRUE(srtp_transport1_->SendRtpPacket(&rtp_packet1to2, options,
+                                                cricket::PF_SRTP_BYPASS));
+    if (srtp_transport1_->IsExternalAuthActive()) {
+      TestRtpAuthParams(srtp_transport1_.get(), cipher_suite_name);
+    } else {
+      ASSERT_TRUE(last_recv_packet2_.data());
+      EXPECT_TRUE(
+          memcmp(last_recv_packet2_.data(), original_rtp_data, rtp_len) == 0);
+      // Get the encrypted packet from underneath packet transport and verify
+      // the data is actually encrypted.
+      auto fake_rtp_packet_transport = static_cast<rtc::FakePacketTransport*>(
+          srtp_transport1_->rtp_packet_transport());
+      EXPECT_FALSE(memcmp(fake_rtp_packet_transport->last_sent_packet()->data(),
+                          original_rtp_data, rtp_len) == 0);
+    }
+
+    // Do the same thing in the opposite direction;
+    ASSERT_TRUE(srtp_transport2_->SendRtpPacket(&rtp_packet2to1, options,
+                                                cricket::PF_SRTP_BYPASS));
+    if (srtp_transport2_->IsExternalAuthActive()) {
+      TestRtpAuthParams(srtp_transport2_.get(), cipher_suite_name);
+    } else {
+      ASSERT_TRUE(last_recv_packet1_.data());
+      EXPECT_TRUE(
+          memcmp(last_recv_packet1_.data(), original_rtp_data, rtp_len) == 0);
+      auto fake_rtp_packet_transport = static_cast<rtc::FakePacketTransport*>(
+          srtp_transport2_->rtp_packet_transport());
+      EXPECT_FALSE(memcmp(fake_rtp_packet_transport->last_sent_packet()->data(),
+                          original_rtp_data, rtp_len) == 0);
+    }
+  }
+
+  void TestSendRecvRtcpPacket(const std::string& cipher_suite_name) {
+    size_t rtcp_len = sizeof(kRtcpReport);
+    size_t packet_size =
+        rtcp_len + 4 + rtc::rtcp_auth_tag_len(cipher_suite_name);
+    rtc::Buffer rtcp_packet_buffer(packet_size);
+    char* rtcp_packet_data = rtcp_packet_buffer.data<char>();
+    memcpy(rtcp_packet_data, kRtcpReport, rtcp_len);
+
+    rtc::CopyOnWriteBuffer rtcp_packet1to2(rtcp_packet_data, rtcp_len,
+                                           packet_size);
+    rtc::CopyOnWriteBuffer rtcp_packet2to1(rtcp_packet_data, rtcp_len,
+                                           packet_size);
+
+    rtc::PacketOptions options;
+    // Send a packet from |srtp_transport1_| to |srtp_transport2_| and verify
+    // that the packet can be successfully received and decrypted.
+    ASSERT_TRUE(srtp_transport1_->SendRtcpPacket(&rtcp_packet1to2, options,
+                                                 cricket::PF_SRTP_BYPASS));
+    ASSERT_TRUE(last_recv_packet2_.data());
+    EXPECT_TRUE(memcmp(last_recv_packet2_.data(), rtcp_packet_data, rtcp_len) ==
+                0);
+    // Get the encrypted packet from underneath packet transport and verify the
+    // data is actually encrypted.
+    auto fake_rtp_packet_transport = static_cast<rtc::FakePacketTransport*>(
+        srtp_transport1_->rtp_packet_transport());
+    EXPECT_FALSE(memcmp(fake_rtp_packet_transport->last_sent_packet()->data(),
+                        rtcp_packet_data, rtcp_len) == 0);
+
+    // Do the same thing in the opposite direction;
+    ASSERT_TRUE(srtp_transport2_->SendRtcpPacket(&rtcp_packet2to1, options,
+                                                 cricket::PF_SRTP_BYPASS));
+    ASSERT_TRUE(last_recv_packet1_.data());
+    EXPECT_TRUE(memcmp(last_recv_packet1_.data(), rtcp_packet_data, rtcp_len) ==
+                0);
+    fake_rtp_packet_transport = static_cast<rtc::FakePacketTransport*>(
+        srtp_transport2_->rtp_packet_transport());
+    EXPECT_FALSE(memcmp(fake_rtp_packet_transport->last_sent_packet()->data(),
+                        rtcp_packet_data, rtcp_len) == 0);
+  }
+
+  void TestSendRecvPacket(bool enable_external_auth,
+                          int cs,
+                          const uint8_t* key1,
+                          int key1_len,
+                          const uint8_t* key2,
+                          int key2_len,
+                          const std::string& cipher_suite_name) {
+    EXPECT_EQ(key1_len, key2_len);
+    EXPECT_EQ(cipher_suite_name, rtc::SrtpCryptoSuiteToName(cs));
+    if (enable_external_auth) {
+      srtp_transport1_->EnableExternalAuth();
+      srtp_transport2_->EnableExternalAuth();
+    }
+    EXPECT_TRUE(
+        srtp_transport1_->SetRtpParams(cs, key1, key1_len, cs, key2, key2_len));
+    EXPECT_TRUE(
+        srtp_transport2_->SetRtpParams(cs, key2, key2_len, cs, key1, key1_len));
+    EXPECT_TRUE(srtp_transport1_->SetRtcpParams(cs, key1, key1_len, cs, key2,
+                                                key2_len));
+    EXPECT_TRUE(srtp_transport2_->SetRtcpParams(cs, key2, key2_len, cs, key1,
+                                                key1_len));
+    EXPECT_TRUE(srtp_transport1_->IsActive());
+    EXPECT_TRUE(srtp_transport2_->IsActive());
+    if (rtc::IsGcmCryptoSuite(cs)) {
+      EXPECT_FALSE(srtp_transport1_->IsExternalAuthActive());
+      EXPECT_FALSE(srtp_transport2_->IsExternalAuthActive());
+    } else if (enable_external_auth) {
+      EXPECT_TRUE(srtp_transport1_->IsExternalAuthActive());
+      EXPECT_TRUE(srtp_transport2_->IsExternalAuthActive());
+    }
+    TestSendRecvRtpPacket(cipher_suite_name);
+    TestSendRecvRtcpPacket(cipher_suite_name);
+  }
+
+  void TestSendRecvPacketWithEncryptedHeaderExtension(
+      const std::string& cs,
+      const std::vector<int>& encrypted_header_ids) {
+    size_t rtp_len = sizeof(kPcmuFrameWithExtensions);
+    size_t packet_size = rtp_len + rtc::rtp_auth_tag_len(cs);
+    rtc::Buffer rtp_packet_buffer(packet_size);
+    char* rtp_packet_data = rtp_packet_buffer.data<char>();
+    memcpy(rtp_packet_data, kPcmuFrameWithExtensions, rtp_len);
+    // In order to be able to run this test function multiple times we can not
+    // use the same sequence number twice. Increase the sequence number by one.
+    rtc::SetBE16(reinterpret_cast<uint8_t*>(rtp_packet_data) + 2,
+                 ++sequence_number_);
+    rtc::CopyOnWriteBuffer rtp_packet1to2(rtp_packet_data, rtp_len,
+                                          packet_size);
+    rtc::CopyOnWriteBuffer rtp_packet2to1(rtp_packet_data, rtp_len,
+                                          packet_size);
+
+    char original_rtp_data[sizeof(kPcmuFrameWithExtensions)];
+    memcpy(original_rtp_data, rtp_packet_data, rtp_len);
+
+    rtc::PacketOptions options;
+    // Send a packet from |srtp_transport1_| to |srtp_transport2_| and verify
+    // that the packet can be successfully received and decrypted.
+    ASSERT_TRUE(srtp_transport1_->SendRtpPacket(&rtp_packet1to2, options,
+                                                cricket::PF_SRTP_BYPASS));
+    ASSERT_TRUE(last_recv_packet2_.data());
+    EXPECT_TRUE(memcmp(last_recv_packet2_.data(), original_rtp_data, rtp_len) ==
+                0);
+    // Get the encrypted packet from underneath packet transport and verify the
+    // data and header extension are actually encrypted.
+    auto fake_rtp_packet_transport = static_cast<rtc::FakePacketTransport*>(
+        srtp_transport1_->rtp_packet_transport());
+    EXPECT_FALSE(memcmp(fake_rtp_packet_transport->last_sent_packet()->data(),
+                        original_rtp_data, rtp_len) == 0);
+    CompareHeaderExtensions(
+        reinterpret_cast<const char*>(
+            fake_rtp_packet_transport->last_sent_packet()->data()),
+        fake_rtp_packet_transport->last_sent_packet()->size(),
+        original_rtp_data, rtp_len, encrypted_header_ids, false);
+
+    // Do the same thing in the opposite direction;
+    ASSERT_TRUE(srtp_transport2_->SendRtpPacket(&rtp_packet2to1, options,
+                                                cricket::PF_SRTP_BYPASS));
+    ASSERT_TRUE(last_recv_packet1_.data());
+    EXPECT_TRUE(memcmp(last_recv_packet1_.data(), original_rtp_data, rtp_len) ==
+                0);
+    fake_rtp_packet_transport = static_cast<rtc::FakePacketTransport*>(
+        srtp_transport2_->rtp_packet_transport());
+    EXPECT_FALSE(memcmp(fake_rtp_packet_transport->last_sent_packet()->data(),
+                        original_rtp_data, rtp_len) == 0);
+    CompareHeaderExtensions(
+        reinterpret_cast<const char*>(
+            fake_rtp_packet_transport->last_sent_packet()->data()),
+        fake_rtp_packet_transport->last_sent_packet()->size(),
+        original_rtp_data, rtp_len, encrypted_header_ids, false);
+  }
+
+  void TestSendRecvEncryptedHeaderExtension(int cs,
+                                            const uint8_t* key1,
+                                            int key1_len,
+                                            const uint8_t* key2,
+                                            int key2_len,
+                                            const std::string& cs_name) {
+    std::vector<int> encrypted_headers;
+    encrypted_headers.push_back(1);
+    // Don't encrypt header ids 2 and 3.
+    encrypted_headers.push_back(4);
+    EXPECT_EQ(key1_len, key2_len);
+    EXPECT_EQ(cs_name, rtc::SrtpCryptoSuiteToName(cs));
+    srtp_transport1_->SetEncryptedHeaderExtensionIds(cricket::CS_LOCAL,
+                                                     encrypted_headers);
+    srtp_transport1_->SetEncryptedHeaderExtensionIds(cricket::CS_REMOTE,
+                                                     encrypted_headers);
+    srtp_transport2_->SetEncryptedHeaderExtensionIds(cricket::CS_LOCAL,
+                                                     encrypted_headers);
+    srtp_transport2_->SetEncryptedHeaderExtensionIds(cricket::CS_REMOTE,
+                                                     encrypted_headers);
+    EXPECT_TRUE(
+        srtp_transport1_->SetRtpParams(cs, key1, key1_len, cs, key2, key2_len));
+    EXPECT_TRUE(
+        srtp_transport2_->SetRtpParams(cs, key2, key2_len, cs, key1, key1_len));
+    EXPECT_TRUE(srtp_transport1_->IsActive());
+    EXPECT_TRUE(srtp_transport2_->IsActive());
+    EXPECT_FALSE(srtp_transport1_->IsExternalAuthActive());
+    EXPECT_FALSE(srtp_transport2_->IsExternalAuthActive());
+    TestSendRecvPacketWithEncryptedHeaderExtension(cs_name, encrypted_headers);
+  }
+
+  std::unique_ptr<SrtpTransport> srtp_transport1_;
+  std::unique_ptr<SrtpTransport> srtp_transport2_;
+
+  std::unique_ptr<rtc::FakePacketTransport> rtp_packet_transport1_;
+  std::unique_ptr<rtc::FakePacketTransport> rtp_packet_transport2_;
+
+  rtc::CopyOnWriteBuffer last_recv_packet1_;
+  rtc::CopyOnWriteBuffer last_recv_packet2_;
+  int sequence_number_ = 0;
 };
 
-TEST(SrtpTransportTest, SendPacket) {
-  auto rtp_transport = rtc::MakeUnique<MockRtpTransport>();
-  EXPECT_CALL(*rtp_transport, SendPacket(_, _, _, _)).WillOnce(Return(true));
+class SrtpTransportTestWithExternalAuth
+    : public SrtpTransportTest,
+      public testing::WithParamInterface<bool> {};
 
-  SrtpTransport srtp_transport(std::move(rtp_transport), "a");
-
-  const bool rtcp = false;
-  rtc::CopyOnWriteBuffer packet;
-  rtc::PacketOptions options;
-  int flags = 0;
-  EXPECT_TRUE(srtp_transport.SendPacket(rtcp, &packet, options, flags));
-
-  // TODO(zstein): Also verify that the packet received by RtpTransport has been
-  // protected once SrtpTransport handles that.
+TEST_P(SrtpTransportTestWithExternalAuth,
+       SendAndRecvPacket_AES_CM_128_HMAC_SHA1_80) {
+  bool enable_external_auth = GetParam();
+  TestSendRecvPacket(enable_external_auth, rtc::SRTP_AES128_CM_SHA1_80,
+                     kTestKey1, kTestKeyLen, kTestKey2, kTestKeyLen,
+                     rtc::CS_AES_CM_128_HMAC_SHA1_80);
 }
 
-// Test that SrtpTransport fires SignalPacketReceived when the underlying
-// RtpTransport fires SignalPacketReceived.
-TEST(SrtpTransportTest, SignalPacketReceived) {
-  auto rtp_transport = rtc::MakeUnique<MockRtpTransport>();
-  MockRtpTransport* rtp_transport_raw = rtp_transport.get();
-  SrtpTransport srtp_transport(std::move(rtp_transport), "a");
+TEST_F(SrtpTransportTest,
+       SendAndRecvPacketWithHeaderExtension_AES_CM_128_HMAC_SHA1_80) {
+  TestSendRecvEncryptedHeaderExtension(rtc::SRTP_AES128_CM_SHA1_80, kTestKey1,
+                                       kTestKeyLen, kTestKey2, kTestKeyLen,
+                                       rtc::CS_AES_CM_128_HMAC_SHA1_80);
+}
 
-  SignalPacketReceivedCounter counter(&srtp_transport);
+TEST_P(SrtpTransportTestWithExternalAuth,
+       SendAndRecvPacket_AES_CM_128_HMAC_SHA1_32) {
+  bool enable_external_auth = GetParam();
+  TestSendRecvPacket(enable_external_auth, rtc::SRTP_AES128_CM_SHA1_32,
+                     kTestKey1, kTestKeyLen, kTestKey2, kTestKeyLen,
+                     rtc::CS_AES_CM_128_HMAC_SHA1_32);
+}
 
-  rtp_transport_raw->PretendReceivedPacket();
+TEST_F(SrtpTransportTest,
+       SendAndRecvPacketWithHeaderExtension_AES_CM_128_HMAC_SHA1_32) {
+  TestSendRecvEncryptedHeaderExtension(rtc::SRTP_AES128_CM_SHA1_32, kTestKey1,
+                                       kTestKeyLen, kTestKey2, kTestKeyLen,
+                                       rtc::CS_AES_CM_128_HMAC_SHA1_32);
+}
 
-  EXPECT_EQ(1, counter.rtp_count());
+TEST_P(SrtpTransportTestWithExternalAuth,
+       SendAndRecvPacket_SRTP_AEAD_AES_128_GCM) {
+  bool enable_external_auth = GetParam();
+  TestSendRecvPacket(enable_external_auth, rtc::SRTP_AEAD_AES_128_GCM,
+                     kTestKeyGcm128_1, kTestKeyGcm128Len, kTestKeyGcm128_2,
+                     kTestKeyGcm128Len, rtc::CS_AEAD_AES_128_GCM);
+}
 
-  // TODO(zstein): Also verify that the packet is unprotected once SrtpTransport
-  // handles that.
+TEST_F(SrtpTransportTest,
+       SendAndRecvPacketWithHeaderExtension_SRTP_AEAD_AES_128_GCM) {
+  TestSendRecvEncryptedHeaderExtension(
+      rtc::SRTP_AEAD_AES_128_GCM, kTestKeyGcm128_1, kTestKeyGcm128Len,
+      kTestKeyGcm128_2, kTestKeyGcm128Len, rtc::CS_AEAD_AES_128_GCM);
+}
+
+TEST_P(SrtpTransportTestWithExternalAuth,
+       SendAndRecvPacket_SRTP_AEAD_AES_256_GCM) {
+  bool enable_external_auth = GetParam();
+  TestSendRecvPacket(enable_external_auth, rtc::SRTP_AEAD_AES_256_GCM,
+                     kTestKeyGcm256_1, kTestKeyGcm256Len, kTestKeyGcm256_2,
+                     kTestKeyGcm256Len, rtc::CS_AEAD_AES_256_GCM);
+}
+
+TEST_F(SrtpTransportTest,
+       SendAndRecvPacketWithHeaderExtension_SRTP_AEAD_AES_256_GCM) {
+  TestSendRecvEncryptedHeaderExtension(
+      rtc::SRTP_AEAD_AES_256_GCM, kTestKeyGcm256_1, kTestKeyGcm256Len,
+      kTestKeyGcm256_2, kTestKeyGcm256Len, rtc::CS_AEAD_AES_256_GCM);
+}
+
+// Run all tests both with and without external auth enabled.
+INSTANTIATE_TEST_CASE_P(ExternalAuth,
+                        SrtpTransportTestWithExternalAuth,
+                        ::testing::Values(true, false));
+
+// Test directly setting the params with bogus keys.
+TEST_F(SrtpTransportTest, TestSetParamsKeyTooShort) {
+  EXPECT_FALSE(srtp_transport1_->SetRtpParams(
+      rtc::SRTP_AES128_CM_SHA1_80, kTestKey1, kTestKeyLen - 1,
+      rtc::SRTP_AES128_CM_SHA1_80, kTestKey1, kTestKeyLen - 1));
+  EXPECT_FALSE(srtp_transport1_->SetRtcpParams(
+      rtc::SRTP_AES128_CM_SHA1_80, kTestKey1, kTestKeyLen - 1,
+      rtc::SRTP_AES128_CM_SHA1_80, kTestKey1, kTestKeyLen - 1));
 }
 
 }  // namespace webrtc