diff --git a/src/encoding/oid.hpp b/src/encoding/oid.hpp
index 7da47a6..d5f99ca 100644
--- a/src/encoding/oid.hpp
+++ b/src/encoding/oid.hpp
@@ -35,14 +35,17 @@
 class OID
 {
 public:
-  OID ()
+  OID()
   {
   }
 
+  explicit
   OID(const char* oid);
 
+  explicit
   OID(const std::string& oid);
 
+  explicit
   OID(const std::vector<int>& oid)
     : m_oid(oid)
   {
@@ -55,19 +58,22 @@
   }
 
   void
-  setIntegerList(const std::vector<int>& value){
+  setIntegerList(const std::vector<int>& value)
+  {
     m_oid = value;
   }
 
   std::string
   toString() const;
 
-  bool operator == (const OID& oid) const
+  bool
+  operator==(const OID& oid) const
   {
     return equal(oid);
   }
 
-  bool operator != (const OID& oid) const
+  bool
+  operator!=(const OID& oid) const
   {
     return !equal(oid);
   }
@@ -90,6 +96,15 @@
   std::vector<int> m_oid;
 };
 
+namespace oid {
+//crypto algorithm
+extern const OID RSA;
+extern const OID ECDSA;
+
+//certificate entries
+extern const OID ATTRIBUTE_NAME;
+}
+
 }
 
 #endif // NDN_ENCODING_OID_HPP