security: Change to use IdentityCertificate instead of Certificate where needed.
diff --git a/include/ndn-cpp/security/identity/memory-identity-storage.hpp b/include/ndn-cpp/security/identity/memory-identity-storage.hpp
index ba0ea5a..cf8f318 100644
--- a/include/ndn-cpp/security/identity/memory-identity-storage.hpp
+++ b/include/ndn-cpp/security/identity/memory-identity-storage.hpp
@@ -113,10 +113,10 @@
 
   /**
    * Add a certificate to the identity storage.
-   * @param certificate The certificate to be added.
+   * @param certificate The certificate to be added.  This makes a copy of the certificate.
    */
   virtual void 
-  addCertificate(const Certificate& certificate);
+  addCertificate(const IdentityCertificate& certificate);
 
   /**
    * Get a certificate from the identity storage.