security: Add doxygen comments

Change-Id: Ieafe4d13513e626d84ef9e621694f69844785018
diff --git a/src/security/certificate-cache.hpp b/src/security/certificate-cache.hpp
index 14c42d1..9d99dcc 100644
--- a/src/security/certificate-cache.hpp
+++ b/src/security/certificate-cache.hpp
@@ -5,14 +5,13 @@
  * See COPYING for copyright and distribution information.
  */
 
-#ifndef NDN_CERTIFICATE_CACHE_HPP
-#define NDN_CERTIFICATE_CACHE_HPP
+#ifndef NDN_SECURITY_CERTIFICATE_CACHE_HPP
+#define NDN_SECURITY_CERTIFICATE_CACHE_HPP
 
 #include "../name.hpp"
 #include "identity-certificate.hpp"
 
-namespace ndn
-{
+namespace ndn {
 
 class CertificateCache
 {
@@ -27,6 +26,6 @@
   getCertificate(const Name& certificateNameWithoutVersion) = 0;
 };
 
-}//ndn
+} // namespace ndn
 
-#endif
+#endif //NDN_SECURITY_CERTIFICATE_CACHE_HPP