diff --git a/src/security/pib/identity.hpp b/src/security/pib/identity.hpp
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+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2013-2016 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_IDENTITY_HPP
+#define NDN_SECURITY_PIB_IDENTITY_HPP
+
+#include "key-container.hpp"
+
+namespace ndn {
+namespace security {
+
+class PibImpl;
+class Pib;
+class IdentityContainer;
+
+/**
+ * @brief represents an identity
+ *
+ * Identity is at the top level in PIB's Identity-Key-Certificate hierarchy.
+ * An identity has a Name, and contains one or more keys, one of which is set
+ * as the default key of this identity.  Properties of a key can be accessed
+ * after obtaining a Key object.
+ *
+ * @throw PibImpl::Error when underlying implementation has non-semantic error.
+ */
+class Identity
+{
+public:
+  friend class Pib;
+  friend class IdentityContainer;
+  friend class KeyChain;
+
+public:
+  /**
+   * @brief Default Constructor
+   *
+   * Identity created using this default constructor is just a place holder.
+   * It must obtain an actual instance from Pib::getIdentity(...).  A typical
+   * usage would be for exception handling:
+   *
+   *   Identity id;
+   *   try {
+   *     id = pib.getIdentity(...);
+   *   }
+   *   catch (Pib::Error&) {
+   *     ...
+   *   }
+   *
+   * An Identity instance created using the constructor is invalid. Calling a
+   * member method on an invalid Identity instance may cause an std::domain_error.
+   */
+  Identity();
+
+  /// @brief Get the name of the identity.
+  const Name&
+  getName() const;
+
+  /**
+   * @brief Get a key with id @p keyId.
+   *
+   * @param keyId The id of the key to get.
+   * @throw Pib::Error if the key does not exist.
+   */
+  Key
+  getKey(const name::Component& keyId) const;
+
+  /// @brief Get all the keys for this Identity.
+  const KeyContainer&
+  getKeys() const;
+
+  /**
+   * @brief Get the default key for this Identity.
+   *
+   * @throws Pib::Error if the default key does not exist.
+   */
+  Key&
+  getDefaultKey() const;
+
+  /// @brief Check if the Identity instance is valid
+  operator bool() const;
+
+  /// @brief Check if the Identity instance is invalid
+  bool
+  operator!() const;
+
+NDN_CXX_PUBLIC_WITH_TESTS_ELSE_PRIVATE: // write operations should be private
+
+  /**
+   * @brief Add a key.
+   *
+   * If the key already exists, do nothing.
+   *
+   * If no default key is set before, the new key will be set as the default key of the identity.
+   *
+   * @param publicKey The public key to add.
+   * @param keyId The key id component of the new key to add.
+   *              By default, the keyId will be set to the hash of the public key bits.
+   * @return the added key or existing key with the same key id.
+   */
+  Key
+  addKey(const v1::PublicKey& publicKey, const name::Component& keyId = EMPTY_KEY_ID);
+
+  /**
+   * @brief Remove a key.
+   *
+   * @param keyId The key id component of the key to delete.
+   */
+  void
+  removeKey(const name::Component& keyId);
+
+  /**
+   * @brief Set the key with id @p keyId as the default key.
+   *
+   * @param keyId The key id component of the default key.
+   * @return The default key
+   * @throws Pib::Error if the key does not exist.
+   */
+  Key&
+  setDefaultKey(const name::Component& keyId);
+
+  /**
+   * @brief Set the default key.
+   *
+   * If the key does not exist, add the key and set it as the default of the Identity.
+   * If the key exists, simply set it as the default key of the Identity.
+   *
+   * @param publicKey The public key to add.
+   * @param keyId The key id component of the default key.
+   * @return the default key
+   */
+  Key&
+  setDefaultKey(const v1::PublicKey& publicKey, const name::Component& keyId = EMPTY_KEY_ID);
+
+NDN_CXX_PUBLIC_WITH_TESTS_ELSE_PRIVATE:
+  /**
+   * @brief Create an Identity with @p identityName.
+   *
+   * @param identityName The name of the Identity.
+   * @param impl The 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.
+   */
+  Identity(const Name& identityName, shared_ptr<PibImpl> impl, bool needInit = false);
+
+  /**
+   * @brief Check the validity of this instance
+   *
+   * @throws std::domain_error if the instance is invalid
+   */
+  void
+  validityCheck() const;
+
+public:
+  /**
+   * @brief The default value of keyId when add a new key.
+   *
+   * An empty keyId implies that the key digest should be used as the actual keyId.
+   */
+  static const name::Component EMPTY_KEY_ID;
+
+private:
+  Name m_name;
+
+  mutable bool m_hasDefaultKey;
+  mutable Key m_defaultKey;
+
+  mutable bool m_needRefreshKeys;
+  mutable KeyContainer m_keys;
+
+  shared_ptr<PibImpl> m_impl;
+};
+
+} // namespace security
+} // namespace ndn
+
+#endif // NDN_SECURITY_PIB_IDENTITY_HPP