diff --git a/src/security/certificate-cache-ttl.cpp b/src/security/certificate-cache-ttl.cpp
new file mode 100644
index 0000000..f5482a3
--- /dev/null
+++ b/src/security/certificate-cache-ttl.cpp
@@ -0,0 +1,72 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil -*- */
+/**
+ * Copyright (C) 2013 Regents of the University of California.
+ * @author: Yingdi Yu <yingdi@cs.ucla.edu>
+ * See COPYING for copyright and distribution information.
+ */
+
+#include "certificate-cache-ttl.hpp"
+
+#include <iostream>
+
+#include "../util/logging.hpp"
+
+
+INIT_LOGGER("CertificateCacheTtl")
+
+using namespace std;
+
+namespace ndn
+{    
+CertificateCacheTtl::CertificateCacheTtl(shared_ptr<boost::asio::io_service> io, int defaultTtl)
+  : m_defaultTtl(defaultTtl)
+  , m_scheduler(*io)
+{}
+
+CertificateCacheTtl::~CertificateCacheTtl()
+{}
+  
+void
+CertificateCacheTtl::insertCertificate(ptr_lib::shared_ptr<const IdentityCertificate> certificate)
+{
+  time::Duration expire = (certificate->getFreshnessPeriod() >= 0 ? time::milliseconds(certificate->getFreshnessPeriod()) : time::seconds(m_defaultTtl));
+
+  Name trackerIndex = certificate->getName().getPrefix(-1);
+  EventTracker::iterator it = m_tracker.find(trackerIndex);
+  if(it != m_tracker.end())
+      m_scheduler.cancelEvent(m_tracker[trackerIndex]);
+
+  m_scheduler.scheduleEvent(time::seconds(0), bind(&CertificateCacheTtl::insert, this, certificate));  
+  m_tracker[trackerIndex] = m_scheduler.scheduleEvent(expire, bind(&CertificateCacheTtl::remove, this, certificate->getName()));
+
+}
+
+void
+CertificateCacheTtl::insert(ptr_lib::shared_ptr<const IdentityCertificate> certificate)
+{ 
+  Name name = certificate->getName().getPrefix(-1);
+  m_cache[name] = certificate;
+}
+
+void
+CertificateCacheTtl::remove(const Name &certificateName)
+{
+  Name name = certificateName.getPrefix(-1);
+  Cache::iterator it = m_cache.find(name);
+  if(it != m_cache.end())
+    m_cache.erase(it);
+}
+
+ptr_lib::shared_ptr<const IdentityCertificate> 
+CertificateCacheTtl::getCertificate(const Name & certificateName)
+{
+  Cache::iterator it = m_cache.find(certificateName);
+  if(it != m_cache.end())
+    return it->second;
+  else
+    return ptr_lib::shared_ptr<IdentityCertificate>();
+}
+
+}//ndn
+
+