security: Added headers for der encoding.  Added CertificateExtension and CertificateSubjectDescription.
diff --git a/Makefile.in b/Makefile.in
index ddbd037..49bb6e2 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -183,6 +183,8 @@
 	ndn-cpp/encoding/element-listener.lo ndn-cpp/encoding/oid.lo \
 	ndn-cpp/encoding/wire-format.lo ndn-cpp/security/key-chain.lo \
 	ndn-cpp/security/security-exception.lo \
+	ndn-cpp/security/certificate/certificate-extension.lo \
+	ndn-cpp/security/certificate/certificate-subject-description.lo \
 	ndn-cpp/security/certificate/public-key.lo \
 	ndn-cpp/security/identity/basic-identity-storage.lo \
 	ndn-cpp/security/identity/identity-manager.lo \
@@ -582,6 +584,8 @@
   include/ndn-cpp/security/security-common.hpp \
   include/ndn-cpp/security/key-chain.hpp \
   include/ndn-cpp/security/security-exception.hpp \
+  include/ndn-cpp/security/certificate/certificate-extension.hpp \
+  include/ndn-cpp/security/certificate/certificate-subject-description.hpp \
   include/ndn-cpp/security/certificate/certificate.hpp \
   include/ndn-cpp/security/certificate/identity-certificate.hpp \
   include/ndn-cpp/security/certificate/public-key.hpp \
@@ -651,8 +655,16 @@
   ndn-cpp/encoding/element-listener.cpp \
   ndn-cpp/encoding/oid.cpp \
   ndn-cpp/encoding/wire-format.cpp \
+  ndn-cpp/encoding/der/der.hpp \
+  ndn-cpp/encoding/der/visitor/no-arguments-visitor.hpp \
+  ndn-cpp/encoding/der/visitor/simple-visitor.hpp \
+  ndn-cpp/encoding/der/visitor/visitor.hpp \
+  ndn-cpp/encoding/der/visitor/void-no-arguments-visitor.hpp \
+  ndn-cpp/encoding/der/visitor/void-visitor.hpp \
   ndn-cpp/security/key-chain.cpp \
   ndn-cpp/security/security-exception.cpp \
+  ndn-cpp/security/certificate/certificate-extension.cpp \
+  ndn-cpp/security/certificate/certificate-subject-description.cpp \
   ndn-cpp/security/certificate/public-key.cpp \
   ndn-cpp/security/identity/basic-identity-storage.cpp \
   ndn-cpp/security/identity/identity-manager.cpp \
@@ -888,6 +900,12 @@
 ndn-cpp/security/certificate/$(DEPDIR)/$(am__dirstamp):
 	@$(MKDIR_P) ndn-cpp/security/certificate/$(DEPDIR)
 	@: > ndn-cpp/security/certificate/$(DEPDIR)/$(am__dirstamp)
+ndn-cpp/security/certificate/certificate-extension.lo:  \
+	ndn-cpp/security/certificate/$(am__dirstamp) \
+	ndn-cpp/security/certificate/$(DEPDIR)/$(am__dirstamp)
+ndn-cpp/security/certificate/certificate-subject-description.lo:  \
+	ndn-cpp/security/certificate/$(am__dirstamp) \
+	ndn-cpp/security/certificate/$(DEPDIR)/$(am__dirstamp)
 ndn-cpp/security/certificate/public-key.lo:  \
 	ndn-cpp/security/certificate/$(am__dirstamp) \
 	ndn-cpp/security/certificate/$(DEPDIR)/$(am__dirstamp)
@@ -1065,6 +1083,8 @@
 @AMDEP_TRUE@@am__include@ @am__quote@ndn-cpp/encoding/$(DEPDIR)/wire-format.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@ndn-cpp/security/$(DEPDIR)/key-chain.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@ndn-cpp/security/$(DEPDIR)/security-exception.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@ndn-cpp/security/certificate/$(DEPDIR)/certificate-extension.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@ndn-cpp/security/certificate/$(DEPDIR)/certificate-subject-description.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@ndn-cpp/security/certificate/$(DEPDIR)/public-key.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@ndn-cpp/security/identity/$(DEPDIR)/basic-identity-storage.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@ndn-cpp/security/identity/$(DEPDIR)/identity-manager.Plo@am__quote@