diff --git a/ndn-cpp/security/key-chain.cpp b/ndn-cpp/security/key-chain.cpp
index a39c4be..5bcc4c1 100644
--- a/ndn-cpp/security/key-chain.cpp
+++ b/ndn-cpp/security/key-chain.cpp
@@ -9,6 +9,7 @@
 #include "../encoding/binary-xml-encoder.hpp"
 #include "../sha256-with-rsa-signature.hpp"
 #include "../util/logging.hpp"
+#include "policy/policy-manager.hpp"
 #include "security-exception.hpp"
 #include "key-chain.hpp"
 
@@ -31,8 +32,8 @@
 };
 #endif
 
-KeyChain::KeyChain(const shared_ptr<IdentityManager>& identityManager)
-: identityManager_(identityManager), face_(0), maxSteps_(100)
+KeyChain::KeyChain(const shared_ptr<IdentityManager>& identityManager, const shared_ptr<PolicyManager>& policyManager)
+: identityManager_(identityManager), policyManager_(policyManager), face_(0), maxSteps_(100)
 {  
 }
 
@@ -98,31 +99,33 @@
 }
 
 void 
-KeyChain::signData(Data& data, const Name& certificateNameIn, WireFormat& wireFormat)
+KeyChain::sign(Data& data, const Name& certificateName, WireFormat& wireFormat)
 {
-  Name inferredCertificateName;
-  const Name* certificateName;
+  identityManager_->signByCertificate(data, certificateName, wireFormat);
+}
+
+void 
+KeyChain::signByIdentity(Data& data, const Name& identityName, WireFormat& wireFormat)
+{
+  Name signingCertificateName;
   
-  if (certificateNameIn.getComponentCount() == 0) {
-#if 0
-    inferredCertificateName = identityManager_->getDefaultCertificateNameForIdentity(policyManager_->inferSigningIdentity(data.getName ()));
-#else
-    inferredCertificateName = Name();
-#endif
-    if (inferredCertificateName.getComponentCount() == 0)
-      throw SecurityException("No qualified certificate name can be inferred");
-    
-    certificateName = &inferredCertificateName;
+  if (identityName.getComponentCount() == 0) {
+    Name inferredIdentity = policyManager_->inferSigningIdentity(data.getName());
+    if (inferredIdentity.getComponentCount() == 0)
+      signingCertificateName = identityManager_->getDefaultCertificateName();
+    else
+      signingCertificateName = identityManager_->getDefaultCertificateNameForIdentity(inferredIdentity);    
   }
   else
-    certificateName = &certificateNameIn;
-        
-#if 0
-  if (!policyManager_->checkSigningPolicy (data.getName (), certificateName))
+    signingCertificateName = identityManager_->getDefaultCertificateNameForIdentity(identityName);
+
+  if (signingCertificateName.getComponentCount() == 0)
+    throw SecurityException("No qualified certificate name found!");
+
+  if (!policyManager_->checkSigningPolicy(data.getName(), signingCertificateName))
     throw SecurityException("Signing Cert name does not comply with signing policy");
-#endif
-  
-  identityManager_->signByCertificate(data, *certificateName, wireFormat);  
+
+  identityManager_->signByCertificate(data, signingCertificateName);  
 }
 
 void
@@ -140,7 +143,7 @@
 #endif
     onVerified(data);
   else
-    onVerifyFailed();
+    onVerifyFailed(data);
 }
 
 }
diff --git a/ndn-cpp/security/key-chain.hpp b/ndn-cpp/security/key-chain.hpp
index 3340908..ff54aa9 100644
--- a/ndn-cpp/security/key-chain.hpp
+++ b/ndn-cpp/security/key-chain.hpp
@@ -13,6 +13,8 @@
 
 namespace ndn {
 
+class PolicyManager;
+  
 /**
  * An OnVerified function object is used to pass a callback to verifyData to report a successful verification.
  */
@@ -21,7 +23,7 @@
 /**
  * An OnVerifyFailed function object is used to pass a callback to verifyData to report a failed verification.
  */
-typedef func_lib::function<void()> OnVerifyFailed;
+typedef func_lib::function<void(const ptr_lib::shared_ptr<Data>& data)> OnVerifyFailed;
 
 /**
  * Keychain is main class of security library.
@@ -31,33 +33,8 @@
  */
 class KeyChain {
 public:
-  KeyChain(const ptr_lib::shared_ptr<IdentityManager>& identityManager);
-
-  /**
-   * Get the default certificate name for the specified identity, which will be used when signing is performed based on identity.
-   * @param identityName The name of the specified identity.
-   * @return The requested certificate name.
-   */
-  Name
-  getDefaultCertificateNameForIdentity(const Name& identityName)
-  {
-    return identityManager_->getDefaultCertificateNameForIdentity(identityName);
-  }
-  
-  /**
-   * Examine the data packet Name and infer the identity name for signing the content.
-   * @param name The data packet name to examine.
-   * @return A new identity name for signing a data packet.
-   */
-  Name
-  inferSigningIdentity(const Name& name)
-  {
-#if 0
-    policyManager_->inferSigningIdentity(name)
-#else
-    return Name();
-#endif
-  }
+  KeyChain
+    (const ptr_lib::shared_ptr<IdentityManager>& identityManager, const ptr_lib::shared_ptr<PolicyManager>& policyManager);
 
   /**
    * Wire encode the Data object, sign it and set its signature.
@@ -68,14 +45,26 @@
    * @param wireFormat A WireFormat object used to encode the input. If omitted, use WireFormat getDefaultWireFormat().
    */
   void 
-  signData(Data& data, const Name& certificateName = Name(), WireFormat& wireFormat = *WireFormat::getDefaultWireFormat());
+  sign(Data& data, const Name& certificateName, WireFormat& wireFormat = *WireFormat::getDefaultWireFormat());
+
+  /**
+   * Wire encode the Data object, sign it and set its signature.
+   * Note: the caller must make sure the timestamp is correct, for example with 
+   * data.getMetaInfo().setTimestampMilliseconds(time(NULL) * 1000.0).
+   * @param data The Data object to be signed.  This updates its signature and key locator field and wireEncoding.
+   * @param identityName The identity name for the key to use for signing.  If omitted, infer the signing identity from the data packet name.
+   * @param wireFormat A WireFormat object used to encode the input. If omitted, use WireFormat getDefaultWireFormat().
+   */
+  void 
+  signByIdentity(Data& data, const Name& identityName = Name(), WireFormat& wireFormat = *WireFormat::getDefaultWireFormat());
 
   /**
    * Check the signature on the Data object and call either onVerify or onVerifyFailed. 
    * We use callback functions because verify may fetch information to check the signature.
-   * @param data
-   * @param onVerified
-   * @param onVerifyFailed
+   * @param data The Data object with the signature to check. It is an error if data does not have a wireEncoding. 
+   * To set the wireEncoding, you can call data.wireDecode.
+   * @param onVerified If the signature is verified, this calls onVerified(data).
+   * @param onVerifyFailed If the signature check fails, this calls onVerifyFailed(data).
    */
   void
   verifyData
@@ -90,6 +79,7 @@
 
 private:
   ptr_lib::shared_ptr<IdentityManager> identityManager_;
+  ptr_lib::shared_ptr<PolicyManager> policyManager_;
   Face* face_;
   const int maxSteps_;
 };