diff --git a/ndn-cpp/fields/signed-blob.h b/ndn-cpp/fields/signed-blob.h
index 2686977..fd5bf90 100644
--- a/ndn-cpp/fields/signed-blob.h
+++ b/ndn-cpp/fields/signed-blob.h
@@ -17,6 +17,10 @@
 
 namespace ndn {
 
+class SignedBlob;
+typedef boost::shared_ptr<SignedBlob> SignedBlobPtr;
+typedef boost::shared_ptr<const SignedBlob> ConstSignedBlobPtr;
+
 /**
  * @brief Class representing a blob, which has a signed portion (e.g., bytes of DATA packet)
  */
@@ -92,7 +96,6 @@
   return m_signedEnd - m_signedBegin;
 }
 
-
 } // ndn
 
 #endif // NDN_SIGNED_BLOB_H