diff --git a/ndn-cpp/security/identity/identity-storage.hpp b/ndn-cpp/security/identity/identity-storage.hpp
index daead73..0e22432 100644
--- a/ndn-cpp/security/identity/identity-storage.hpp
+++ b/ndn-cpp/security/identity/identity-storage.hpp
@@ -83,7 +83,7 @@
    * @param publicKeyDer A blob of the public key DER to be added.
    */
   virtual void 
-  addKey(const Name& keyName, KeyType keyType, Blob& publicKeyDer) = 0;
+  addKey(const Name& keyName, KeyType keyType, const Blob& publicKeyDer) = 0;
 
   /**
    * Get the public key DER blob from the identity storage.
diff --git a/ndn-cpp/security/identity/memory-identity-storage.cpp b/ndn-cpp/security/identity/memory-identity-storage.cpp
index 1e4f0fc..587d231 100644
--- a/ndn-cpp/security/identity/memory-identity-storage.cpp
+++ b/ndn-cpp/security/identity/memory-identity-storage.cpp
@@ -73,7 +73,7 @@
 }
 
 void 
-MemoryIdentityStorage::addKey(const Name& keyName, KeyType keyType, Blob& publicKeyDer)
+MemoryIdentityStorage::addKey(const Name& keyName, KeyType keyType, const Blob& publicKeyDer)
 {
 #if 1
   throw std::runtime_error("MemoryIdentityStorage::addKey not implemented");
diff --git a/ndn-cpp/security/identity/memory-identity-storage.hpp b/ndn-cpp/security/identity/memory-identity-storage.hpp
index dc8509d..980f78d 100644
--- a/ndn-cpp/security/identity/memory-identity-storage.hpp
+++ b/ndn-cpp/security/identity/memory-identity-storage.hpp
@@ -79,7 +79,7 @@
    * @param publicKeyDer A blob of the public key DER to be added.
    */
   virtual void 
-  addKey(const Name& keyName, KeyType keyType, Blob& publicKeyDer);
+  addKey(const Name& keyName, KeyType keyType, const Blob& publicKeyDer);
 
   /**
    * Get the public key DER blob from the identity storage.