diff --git a/src/security/pib/detail/identity-impl.hpp b/src/security/pib/detail/identity-impl.hpp
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+++ b/src/security/pib/detail/identity-impl.hpp
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+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2013-2017 Regents of the University of California.
+ *
+ * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
+ *
+ * ndn-cxx library is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later version.
+ *
+ * ndn-cxx library is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more details.
+ *
+ * You should have received copies of the GNU General Public License and GNU Lesser
+ * General Public License along with ndn-cxx, e.g., in COPYING.md file.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ * See AUTHORS.md for complete list of ndn-cxx authors and contributors.
+ */
+
+#ifndef NDN_SECURITY_PIB_DETAIL_IDENTITY_IMPL_HPP
+#define NDN_SECURITY_PIB_DETAIL_IDENTITY_IMPL_HPP
+
+#include "../key-container.hpp"
+
+namespace ndn {
+namespace security {
+namespace pib {
+
+class PibImpl;
+
+namespace detail {
+
+/**
+ * @brief Backend instance of Identity
+ *
+ * An Identity has only one backend instance, but may have multiple frontend handles.
+ * Each frontend handle is associated with the only one backend IdentityImpl.
+ *
+ * @throw PibImpl::Error when underlying implementation has non-semantic error.
+ */
+class IdentityImpl : noncopyable
+{
+public:
+  /**
+   * @brief Create an Identity with @p identityName.
+   *
+   * @param identityName The name of the Identity.
+   * @param impl The PIB backend implementation.
+   * @param needInit If true, create the identity in backend when the identity does not exist.
+   *                 Otherwise, throw Pib::Error when the identity does not exist.
+   */
+  IdentityImpl(const Name& identityName, shared_ptr<PibImpl> impl, bool needInit = false);
+
+  /// @brief Get the name of the identity.
+  const Name&
+  getName() const
+  {
+    return m_name;
+  }
+
+  /**
+   * @brief Add a @p key of @p keyLen bytes with @p keyName (in PKCS#8 format).
+   *
+   * If no default key is set before, the new key will be set as the default key of the identity.
+   *
+   * @return the added key.
+   * @throw std::invalid_argument key name does not match identity
+   * @throw Pib::Error a key with the same name already exists
+   */
+  Key
+  addKey(const uint8_t* key, size_t keyLen, const Name& keyName);
+
+  /**
+   * @brief Remove a key with @p keyName
+   * @throw std::invalid_argument @p keyName does not match identity
+   */
+  void
+  removeKey(const Name& keyName);
+
+  /**
+   * @brief Get a key with id @p keyName.
+   *
+   * @throw std::invalid_argument @p keyName does not match identity
+   * @throw Pib::Error the key does not exist.
+   */
+  Key
+  getKey(const Name& keyName) const;
+
+  /**
+   * @brief Get all keys for this Identity.
+   */
+  const KeyContainer&
+  getKeys() const;
+
+  /**
+   * @brief Set the key with id @p keyName.
+   * @throw std::invalid_argument @p keyName does not match identity
+   * @throw Pib::Error the key does not exist.
+   * @return The default key
+   */
+  const Key&
+  setDefaultKey(const Name& keyName);
+
+  /**
+   * @brief Add @p key of @p keyLen bytes with @p keyName and set it as the default key
+   * @throw std::invalid_argument @p keyName does not match identity
+   * @throw Pib::Error the key with the same name already exists
+   * @return the default key
+   */
+  const Key&
+  setDefaultKey(const uint8_t* key, size_t keyLen, const Name& keyName);
+
+  /**
+   * @brief Get the default key for this Identity.
+   * @throw Pib::Error the default key does not exist.
+   */
+  const Key&
+  getDefaultKey() const;
+
+private:
+  Name m_name;
+
+  mutable bool m_isDefaultKeyLoaded;
+  mutable Key m_defaultKey;
+
+  mutable KeyContainer m_keys;
+
+  shared_ptr<PibImpl> m_impl;
+};
+
+} // namespace detail
+} // namespace pib
+} // namespace security
+} // namespace ndn
+
+#endif // NDN_SECURITY_PIB_DETAIL_IDENTITY_IMPL_HPP