Cast: Added support for AES-CTR crypto.

media/cast/audio_sender/audio_sender.cc

Index: media/cast/audio_sender/audio_sender.cc
diff --git a/media/cast/audio_sender/audio_sender.cc b/media/cast/audio_sender/audio_sender.cc
index 560ebd990ccaf094ffbd41726762e9978c16a6aa..6c05044284fb9f79783125f7056209af71de1837 100644
--- a/media/cast/audio_sender/audio_sender.cc
+++ b/media/cast/audio_sender/audio_sender.cc
@@ -7,6 +7,7 @@
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
+#include "crypto/symmetric_key.h"
 #include "media/cast/audio_sender/audio_encoder.h"
 #include "media/cast/rtcp/rtcp.h"
 #include "media/cast/rtp_sender/rtp_sender.h"
@@ -93,6 +94,18 @@ AudioSender::AudioSender(scoped_refptr<CastEnvironment> cast_environment,
               audio_config.sender_ssrc,
               audio_config.rtcp_c_name),
         weak_factory_(this) {
+  if (audio_config.aes_iv_mask.size() == kAesKeySize &&
+      audio_config.aes_key.size() == kAesKeySize) {
+    iv_mask_ = audio_config.aes_iv_mask;
+    crypto::SymmetricKey* key = crypto::SymmetricKey::Import(
+        crypto::SymmetricKey::AES, audio_config.aes_key);
+    encryptor_.reset(new crypto::Encryptor());
+    encryptor_->Init(key, crypto::Encryptor::CTR, std::string());
+  } else if (audio_config.aes_iv_mask.size() != 0 ||
+             audio_config.aes_key.size() != 0) {
+    DCHECK(false) << "Invalid crypto configuration";
+  }
+
   rtcp_.SetRemoteSSRC(audio_config.incoming_feedback_ssrc);
 
   if (!audio_config.use_external_encoder) {
@@ -119,14 +132,48 @@ void AudioSender::InsertCodedAudioFrame(const EncodedAudioFrame* audio_frame,
                                         const base::TimeTicks& recorded_time,
                                         const base::Closure callback) {
   DCHECK(audio_encoder_.get() == NULL) << "Invalid internal state";
-  rtp_sender_.IncomingEncodedAudioFrame(audio_frame, recorded_time);
+
+  if (encryptor_) {
+    EncodedAudioFrame encrypted_frame;
+    if (EncryptAudioFrame(audio_frame, &encrypted_frame)) {
+      rtp_sender_.IncomingEncodedAudioFrame(&encrypted_frame, recorded_time);
+    } else {
+      DCHECK(false) << "Encryption error";

[wtc, 2013/11/13 20:57:17]

Nit: use NOTREACHED() instead of DCHECK(false).

[pwestin, 2013/11/15 19:38:17]

Done.

+      return;
+    }
+  } else {
+    rtp_sender_.IncomingEncodedAudioFrame(audio_frame, recorded_time);
+  }

[wtc, 2013/11/13 20:57:17]

Nit: it would be better to avoid having two
rtp_sender_.IncomingEncodedAudioFrame() calls. But this is fine, too.

[pwestin, 2013/11/15 19:38:17]

ok

   callback.Run();
 }
 
+bool AudioSender::EncryptAudioFrame(const EncodedAudioFrame* audio_frame,
+                                    EncodedAudioFrame* encrypted_frame) {
+  DCHECK(encryptor_) << "Invalid state";
+
+  encryptor_->SetCounter(GetAesNounce(audio_frame->frame_id, iv_mask_));
+
+  encrypted_frame->codec = audio_frame->codec;
+  encrypted_frame->frame_id = audio_frame->frame_id;
+  encrypted_frame->samples = audio_frame->samples;
+
+  return encryptor_->Encrypt(audio_frame->data, &encrypted_frame->data);

[wtc, 2013/11/13 20:57:17]

Nit: in another file you seem to take care to not modify the output argument
unless the function returns true. I am not sure if we should also do that here.

[pwestin, 2013/11/15 19:38:17]

Done.

+}
+
 void AudioSender::SendEncodedAudioFrame(
     scoped_ptr<EncodedAudioFrame> audio_frame,
     const base::TimeTicks& recorded_time) {
-  rtp_sender_.IncomingEncodedAudioFrame(audio_frame.get(), recorded_time);
+  if (encryptor_) {
+    EncodedAudioFrame encrypted_frame;
+    if (EncryptAudioFrame(audio_frame.get(), &encrypted_frame)) {
+      rtp_sender_.IncomingEncodedAudioFrame(&encrypted_frame, recorded_time);
+    } else {
+      DCHECK(false) << "Encryption error";
+      return;
+    }
+  } else {
+    rtp_sender_.IncomingEncodedAudioFrame(audio_frame.get(), recorded_time);
+  }

[wtc, 2013/11/13 20:57:17]

Nit: this method is extremely similar to InsertCodedAudioFrame(). The only
differences are:

1) whether |audio_frame| is a plain pointer or a scoped_ptr.
2) InsertCodedAudioFrame does callback.Run() at the end.

I wonder if it is possible to share code.

[pwestin, 2013/11/15 19:38:17]

It's not a trivial change so I will leave that to another cl

 }
 
 void AudioSender::ResendPackets(