diff --git a/ndn-cpp/key-chain.hpp b/ndn-cpp/key-chain.hpp
index cef43e1..2259064 100644
--- a/ndn-cpp/key-chain.hpp
+++ b/ndn-cpp/key-chain.hpp
@@ -13,7 +13,9 @@
 class KeyChain {
 public:
   /**
-   * In data, set the signed info key to the default public key and set the signature using the default private key.
+   * In data, set the signed info publisher public key digest and key locator key to the default public key and set the 
+   * signature using the default private key.
+   * Note: the caller must make sure the timestamp is correct with data.getSignedInfo().setTimestampMilliseconds.
    * @param data The Data object to sign and set the signature.
    */
   static void defaultSign(Data &data);