diff --git a/ndn-cpp/security/key-chain.cpp b/ndn-cpp/security/key-chain.cpp
index 3fc3f77..c17960d 100644
--- a/ndn-cpp/security/key-chain.cpp
+++ b/ndn-cpp/security/key-chain.cpp
@@ -104,6 +104,12 @@
   identityManager_->signByCertificate(data, certificateName, wireFormat);
 }
 
+shared_ptr<Signature> 
+KeyChain::sign(const uint8_t* buffer, size_t bufferLength, const Name& certificateName)
+{
+  return identityManager_->signByCertificate(buffer, bufferLength, certificateName);
+}
+
 void 
 KeyChain::signByIdentity(Data& data, const Name& identityName, WireFormat& wireFormat)
 {
@@ -128,6 +134,17 @@
   identityManager_->signByCertificate(data, signingCertificateName);  
 }
 
+  shared_ptr<Signature> 
+  KeyChain::signByIdentity(const uint8_t* buffer, size_t bufferLength, const Name& identityName)
+  {
+    Name signingCertificateName = identityManager_->getDefaultCertificateNameForIdentity(identityName);
+    
+    if (signingCertificateName.size() == 0)
+      throw SecurityException("No qualified certificate name found!");
+
+    return identityManager_->signByCertificate(buffer, bufferLength, signingCertificateName);
+  }
+
 void
 KeyChain::verifyData
   (const shared_ptr<Data>& data, const OnVerified& onVerified, const OnVerifyFailed& onVerifyFailed, int stepCount)