diff --git a/include/ndn-cpp/security/identity/private-key-storage.hpp b/include/ndn-cpp/security/identity/private-key-storage.hpp
index 9777d64..5446484 100644
--- a/include/ndn-cpp/security/identity/private-key-storage.hpp
+++ b/include/ndn-cpp/security/identity/private-key-storage.hpp
@@ -55,12 +55,10 @@
    */  
   virtual Block
   sign(const uint8_t *data, size_t dataLength,
-       const Signature &signature,
        const Name& keyName, DigestAlgorithm digestAlgorithm = DIGEST_ALGORITHM_SHA256) = 0;
 
-  virtual Block
-  sign(const Data &data,
-       const Signature &signature,
+  virtual void
+  sign(Data &data,
        const Name& keyName, DigestAlgorithm digestAlgorithm = DIGEST_ALGORITHM_SHA256) = 0;
   
   /**