Move key-chain to security subdirectory.
diff --git a/ndn-cpp/node.cpp b/ndn-cpp/node.cpp
index 369f3ca..a93ebd7 100644
--- a/ndn-cpp/node.cpp
+++ b/ndn-cpp/node.cpp
@@ -57,6 +57,7 @@
 {
   if (ndndIdData->getSignedInfo().getPublisherPublicKeyDigest().getPublisherPublicKeyDigest().size() > 0) {
     // Set the ndndId_ and continue.
+    // TODO: If there are multiple connected hubs, the NDN ID is really stored per connected hub.
     info_->node_.ndndId_ = ndndIdData->getSignedInfo().getPublisherPublicKeyDigest().getPublisherPublicKeyDigest();
     info_->node_.registerPrefixHelper(info_->prefix_, info_->onInterest_, info_->flags_);
   }