diff --git a/include/ndn-cpp/common.hpp b/include/ndn-cpp/common.hpp
index e9d0c88..a4ced37 100644
--- a/include/ndn-cpp/common.hpp
+++ b/include/ndn-cpp/common.hpp
@@ -53,6 +53,9 @@
 
 namespace ndn {
    
+// TODO: Implement Time, used in certificates and DER encoding.
+typedef double Time;  
+  
 /**
  * Return the hex representation of the bytes in array.
  * @param array The array of bytes.