Create the SrtpTransportInterface.

webrtc/api/ortc/srtptransportinterface.h

+/*
+ *  Copyright 2017 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_API_ORTC_SRTPTRANSPORTINTERFACE_H_
+#define WEBRTC_API_ORTC_SRTPTRANSPORTINTERFACE_H_
+
+#include "webrtc/api/ortc/rtptransportinterface.h"
+#include "webrtc/api/rtcerror.h"
+#include "webrtc/media/base/cryptoparams.h"
+
+namespace webrtc {
+
+// The subclass of the RtpTransport which uses SRTP. The keying information
+// is explicitly passed in from the application.
+//
+// If using SDP and SDES (RFC4568) for signaling, then after applying the
+// answer, the negotiated keying information from the offer and answer would be
+// set and the SRTP would be active.
+//
+// Note that Edge's implementation of ORTC provides a similar API point, called
+// RTCSrtpSdesTransport:
+// https://msdn.microsoft.com/en-us/library/mt502527(v=vs.85).aspx
+class SrtpTransportInterface : public RtpTransportInterface {
+ public:
+  virtual ~SrtpTransportInterface() {}
+
+  // There are some limitations of current implementation:

[pthatcher1, 2017/03/03 06:28:38]

the current implementation

[Zhi Huang, 2017/03/03 22:34:47]

I made a lot of mistakes like this recently. Maybe someone can teach me how to
use "the". :)

+  //  1. Send and receive keys must use the same crypto suite.
+  //  2. The keys can't be changed after initially set.
+  //  3. The keys must be set before creating a sender/receiver using the SRTP
+  //     transport.
+  // Set the SRTP keying material for outgoing streams.
+  virtual RTCError SetSrtpSendKey(const cricket::CryptoParams& params) = 0;
+
+  // Set the SRTP keying material for incoming streams.

[pthatcher1, 2017/03/03 06:28:38]

Isn't it for incoming streams and RTCP?  Might as well just say for receiving
RTP and RTCP.  

[Zhi Huang, 2017/03/03 22:34:47]

Done.

+  virtual RTCError SetSrtpReceiveKey(const cricket::CryptoParams& params) = 0;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_API_ORTC_SRTPTRANSPORTINTERFACE_H_