diff --git a/include/ndn-cpp-dev/security/key-chain.hpp b/include/ndn-cpp-dev/security/key-chain.hpp
index fffa05d..c5df5db 100644
--- a/include/ndn-cpp-dev/security/key-chain.hpp
+++ b/include/ndn-cpp-dev/security/key-chain.hpp
@@ -153,6 +153,22 @@
     return certificate;
   }
 
+  /**
+   * Fetch the private key for keyName and sign the data, and set the signature block of the data packet.
+   * Throw Error if signing fails.
+   * @param data Reference to the input data packet.
+   * @param keyName The name of the signing key.
+   * @param digestAlgorithm the digest algorithm.
+   */  
+  void
+  signInTpm(Data &data, const Name& keyName, DigestAlgorithm digestAlgorithm)
+  {
+    data.setSignatureValue
+      (Tpm::signInTpm(data.wireEncode().value(),
+                      data.wireEncode().value_size() - data.getSignature().getValue().size(),
+                      keyName, digestAlgorithm));
+  }
+
   void
   sign(Data &data)
   {
@@ -184,7 +200,7 @@
     data.setSignature(signature);
 
     // For temporary usage, we support RSA + SHA256 only, but will support more.
-    Tpm::signInTpm(data, cert->getPublicKeyName(), DIGEST_ALGORITHM_SHA256);
+    signInTpm(data, cert->getPublicKeyName(), DIGEST_ALGORITHM_SHA256);
   }
 
   void
@@ -195,7 +211,7 @@
     data.setSignature(signature);
 
     // For temporary usage, we support RSA + SHA256 only, but will support more.
-    Tpm::signInTpm(data, certificate.getPublicKeyName(), DIGEST_ALGORITHM_SHA256);
+    signInTpm(data, certificate.getPublicKeyName(), DIGEST_ALGORITHM_SHA256);
   }
   
   /**
@@ -296,7 +312,7 @@
     cert.setSignature(signature);
 
     // For temporary usage, we support RSA + SHA256 only, but will support more.
-    Tpm::signInTpm(cert, cert.getPublicKeyName(), DIGEST_ALGORITHM_SHA256);
+    signInTpm(cert, cert.getPublicKeyName(), DIGEST_ALGORITHM_SHA256);
   }
 
 
diff --git a/include/ndn-cpp-dev/security/sec-tpm-memory.hpp b/include/ndn-cpp-dev/security/sec-tpm-memory.hpp
index 8203272..21dc272 100644
--- a/include/ndn-cpp-dev/security/sec-tpm-memory.hpp
+++ b/include/ndn-cpp-dev/security/sec-tpm-memory.hpp
@@ -68,9 +68,6 @@
    */  
   virtual Block 
   signInTpm(const uint8_t *data, size_t dataLength, const Name& keyName, DigestAlgorithm digestAlgorithm);
-
-  virtual void 
-  signInTpm(Data &data, const Name& keyName, DigestAlgorithm digestAlgorithm);
   
   /**
    * Decrypt data.
diff --git a/include/ndn-cpp-dev/security/sec-tpm-osx.hpp b/include/ndn-cpp-dev/security/sec-tpm-osx.hpp
index 4839e3d..2ea9ff1 100644
--- a/include/ndn-cpp-dev/security/sec-tpm-osx.hpp
+++ b/include/ndn-cpp-dev/security/sec-tpm-osx.hpp
@@ -37,16 +37,13 @@
 
   // From TrustedPlatformModule
   virtual void 
-  generateKeyPairInTpm(const Name& keyName, KeyType keyType = KEY_TYPE_RSA, int keySize = 2048);
+  generateKeyPairInTpm(const Name& keyName, KeyType keyType, int keySize);
 
   virtual ptr_lib::shared_ptr<PublicKey> 
   getPublicKeyFromTpm(const Name& keyName);
   
   virtual Block
   signInTpm(const uint8_t *data, size_t dataLength, const Name& keyName, DigestAlgorithm digestAlgorithm);
-
-  virtual void
-  signInTpm(Data &data, const Name& keyName, DigestAlgorithm digestAlgorithm);
   
   /**
    * Decrypt data.
diff --git a/include/ndn-cpp-dev/security/sec-tpm.hpp b/include/ndn-cpp-dev/security/sec-tpm.hpp
index c6b5328..dd9a55e 100644
--- a/include/ndn-cpp-dev/security/sec-tpm.hpp
+++ b/include/ndn-cpp-dev/security/sec-tpm.hpp
@@ -45,18 +45,16 @@
   getPublicKeyFromTpm(const Name& keyName) = 0;
   
   /**
-   * Fetch the private key for keyName and sign the data, returning a signature Blob.
+   * Fetch the private key for keyName and sign the data, returning a signature block.
    * @param data Pointer to the input byte array.
    * @param dataLength The length of data.
    * @param keyName The name of the signing key.
    * @param digestAlgorithm the digest algorithm.
-   * @return The signature, or a null pointer if signing fails.
+   * @return The signature block.
+   * @throws SecTpm::Error
    */  
   virtual Block
   signInTpm(const uint8_t *data, size_t dataLength, const Name& keyName, DigestAlgorithm digestAlgorithm) = 0;
-
-  virtual void
-  signInTpm(Data &data, const Name& keyName, DigestAlgorithm digestAlgorithm) = 0;
   
   /**
    * Decrypt data.