[Cast Channel] Add support for nonce challenge to Cast channel authentication.

extensions/browser/api/cast_channel/cast_socket.cc

Index: extensions/browser/api/cast_channel/cast_socket.cc
diff --git a/extensions/browser/api/cast_channel/cast_socket.cc b/extensions/browser/api/cast_channel/cast_socket.cc
index 3bb675cf3fd9f74b4424d13044a8cf14ba0d7d99..6ba7e934bd8a75b772053c76f0ecca59dda49bf7 100644
--- a/extensions/browser/api/cast_channel/cast_socket.cc
+++ b/extensions/browser/api/cast_channel/cast_socket.cc
@@ -12,6 +12,7 @@
 #include "base/bind.h"
 #include "base/callback_helpers.h"
 #include "base/format_macros.h"
+#include "base/guid.h"
 #include "base/lazy_instance.h"
 #include "base/location.h"
 #include "base/memory/ptr_util.h"
@@ -73,6 +74,8 @@ namespace api {
 namespace cast_channel {
 namespace {
 
+long kNonceExpirationTimeInHours = 24;
+
 bool IsTerminalState(proto::ConnectionState state) {
   return state == proto::CONN_STATE_FINISHED ||
          state == proto::CONN_STATE_ERROR || state == proto::CONN_STATE_TIMEOUT;
@@ -98,6 +101,22 @@ class FakeCertVerifier : public net::CertVerifier {
 
 }  // namespace
 
+// static
+std::string CastSocketImpl::nonce_ = "";

[mark a. foltz, 2017/03/03 23:25:51]

Static variables must be POD (with a few exceptions).  Use base::Singleton.

https://google.github.io/styleguide/cppguide.html#Static_and_Global_Variables

[ryanchung, 2017/03/06 22:57:46]

Done. Thanks.

+// static
+base::Time CastSocketImpl::nonce_generation_time_ = base::Time();
+
+// static
+void CastSocketImpl::EnsureNonceTimely() {
+  if (nonce_.empty() ||
+      base::Time::Now() >
+          (nonce_generation_time_ +
+           base::TimeDelta::FromHours(kNonceExpirationTimeInHours))) {
+    nonce_ = base::GenerateGUID();

[mark a. foltz, 2017/03/03 23:25:51]

I thought there was a different nonce for each attempt to open the socket? Is
the concern overuse of /dev/urandom?

[ryanchung, 2017/03/06 22:57:46]

Ideally, each connection attempt uses a difference nonce. The concern is on the
overhead of the signing operation on some of the older generations of receivers.
When the same nonce is used, the signature can be cached so the latency for the
Cast operation roughly cuts in half.

+    nonce_generation_time_ = base::Time::Now();
+  }
+}
+
 CastSocket::CastSocket(const std::string& owner_extension_id)
     : ApiResource(owner_extension_id) {
 }
@@ -134,6 +153,7 @@ CastSocketImpl::CastSocketImpl(const std::string& owner_extension_id,
   DCHECK(net_log_);
   net_log_source_.type = net::NetLogSourceType::SOCKET;
   net_log_source_.id = net_log_->NextID();
+  EnsureNonceTimely();
 }
 
 CastSocketImpl::~CastSocketImpl() {
@@ -235,7 +255,7 @@ bool CastSocketImpl::VerifyChannelPolicy(const AuthResult& result) {
 bool CastSocketImpl::VerifyChallengeReply() {
   DCHECK(peer_cert_);
   AuthResult result =
-      AuthenticateChallengeReply(*challenge_reply_, *peer_cert_);
+      AuthenticateChallengeReply(*challenge_reply_, *peer_cert_, nonce_);
   logger_->LogSocketChallengeReplyEvent(channel_id_, result);
   if (result.success()) {
     VLOG(1) << result.error_message;
@@ -450,7 +470,7 @@ int CastSocketImpl::DoAuthChallengeSend() {
   SetConnectState(proto::CONN_STATE_AUTH_CHALLENGE_SEND_COMPLETE);
 
   CastMessage challenge_message;
-  CreateAuthChallengeMessage(&challenge_message);
+  CreateAuthChallengeMessage(&challenge_message, nonce_);
   VLOG_WITH_CONNECTION(1) << "Sending challenge: "
                           << CastMessageToString(challenge_message);
 
@@ -618,6 +638,7 @@ void CastSocketImpl::SetErrorState(ChannelError error_state) {
   logger_->LogSocketErrorState(channel_id_, ErrorStateToProto(error_state_));
   delegate_->OnError(error_state_);
 }
+
 }  // namespace cast_channel
 }  // namespace api
 }  // namespace extensions