security: Added headers for der encoding. Added CertificateExtension and CertificateSubjectDescription.
diff --git a/ndn-cpp/security/certificate/certificate-subject-description.cpp b/ndn-cpp/security/certificate/certificate-subject-description.cpp
new file mode 100644
index 0000000..ee2310c
--- /dev/null
+++ b/ndn-cpp/security/certificate/certificate-subject-description.cpp
@@ -0,0 +1,31 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil -*- */
+/**
+ * Copyright (C) 2013 Regents of the University of California.
+ * @author: Yingdi Yu <yingdi@cs.ucla.edu>
+ * @author: Jeff Thompson <jefft0@remap.ucla.edu>
+ * See COPYING for copyright and distribution information.
+ */
+
+#include "../../encoding/der/der.hpp"
+#include <ndn-cpp/security/certificate/certificate-subject-description.hpp>
+
+using namespace std;
+using namespace ndn::ptr_lib;
+
+namespace ndn {
+
+shared_ptr<der::DerNode>
+CertificateSubjectDescription::toDer()
+{
+ shared_ptr<der::DerSequence> root(new der::DerSequence());
+
+ shared_ptr<der::DerOid> oid(new der::DerOid(oid_));
+ shared_ptr<der::DerPrintableString> value(new der::DerPrintableString(value_));
+
+ root->addChild(oid);
+ root->addChild(value);
+
+ return root;
+}
+
+}