diff --git a/src/security/transform/private-key.hpp b/src/security/transform/private-key.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_CXX_SECURITY_TRANSFORM_PRIVATE_KEY_HPP
+#define NDN_CXX_SECURITY_TRANSFORM_PRIVATE_KEY_HPP
+
+#include "public-key.hpp"
+#include "../../encoding/buffer.hpp"
+
+namespace ndn {
+
+class KeyParams;
+
+namespace security {
+namespace transform {
+
+/**
+ * @brief Abstraction of private key in crypto transformation
+ */
+class PrivateKey : noncopyable
+{
+public:
+  class Error : public std::runtime_error
+  {
+  public:
+    explicit
+    Error(const std::string& what)
+      : std::runtime_error(what)
+    {
+    }
+  };
+
+  friend class SignerFilter;
+
+  /**
+   * @brief Callback for application to handle password input
+   *
+   * Password should be stored in @p buf and should not be longer than @p size.  It is
+   * recommended to ask the user to verify the passphrase if @p shouldConfirm is true, e.g., by
+   * prompting for the password twice.
+   */
+  typedef function<int(char* buf, size_t bufSize, bool shouldConfirm)> PasswordCallback;
+
+public:
+  /**
+   * @brief Create a private key instance
+   *
+   * One must call loadXXXX(...) to load private key.
+   */
+  PrivateKey();
+
+  ~PrivateKey();
+
+  /**
+   * @brief Load the private key in PKCS#1 format from a buffer @p buf
+   */
+  void
+  loadPkcs1(const uint8_t* buf, size_t size);
+
+  /**
+   * @brief Load the private key in PKCS#1 format from a stream @p is
+   */
+  void
+  loadPkcs1(std::istream& is);
+
+  /**
+   * @brief Load the private key in base64-encoded PKCS#1 format from a buffer @p buf
+   */
+  void
+  loadPkcs1Base64(const uint8_t* buf, size_t size);
+
+  /**
+   * @brief Load the private key in base64-encoded PKCS#1 format from a stream @p is
+   */
+  void
+  loadPkcs1Base64(std::istream& is);
+
+  /**
+   * @brief Load the private key in encrypted PKCS#8 format from a buffer @p buf with passphrase @p pw
+   *
+   * @pre strlen(pw) == pwLen
+   */
+  void
+  loadPkcs8(const uint8_t* buf, size_t size, const char* pw, size_t pwLen);
+
+  /**
+   * @brief Load the private key in encrypted PKCS#8 format from a buffer @p buf with
+   *        passphrase obtained from @p pwCallback
+   *
+   * The default password callback is provided by OpenSSL
+   */
+  void
+  loadPkcs8(const uint8_t* buf, size_t size, PasswordCallback pwCallback = nullptr);
+
+  /**
+   * @brief Load the private key in encrypted PKCS#8 format from a stream @p is with passphrase @p pw
+   *
+   * @pre strlen(pw) == pwLen
+   */
+  void
+  loadPkcs8(std::istream& is, const char* pw, size_t pwLen);
+
+  /**
+   * @brief Load the private key in encrypted PKCS#8 format from a stream @p is with passphrase
+   *        obtained from @p pwCallback
+   *
+   * The default password callback is provided by OpenSSL
+   */
+  void
+  loadPkcs8(std::istream& is, PasswordCallback pwCallback = nullptr);
+
+  /**
+   * @brief Load the private key in base64-encoded encrypted PKCS#8 format from a buffer @p buf
+   *        with passphrase @p pw
+   *
+   * @pre strlen(pw) == pwLen
+   */
+  void
+  loadPkcs8Base64(const uint8_t* buf, size_t size, const char* pw, size_t pwLen);
+
+  /**
+   * @brief Load the private key in encrypted PKCS#8 format from a buffer @p buf with
+   *        passphrase obtained from @p pwCallback
+   *
+   * The default password callback is provided by OpenSSL
+   */
+  void
+  loadPkcs8Base64(const uint8_t* buf, size_t size, PasswordCallback pwCallback = nullptr);
+
+  /**
+   * @brief Load the private key in base64-encoded encrypted PKCS#8 format from a stream @p is
+   *        with passphrase @p pw
+   *
+   * @pre strlen(pw) == pwLen
+   */
+  void
+  loadPkcs8Base64(std::istream& is, const char* pw, size_t pwLen);
+
+  /**
+   * @brief Load the private key in base64-encoded encrypted PKCS#8 format from a stream @p is
+   *        with passphrase obtained from @p pwCallback
+   *
+   * The default password callback is provided by OpenSSL
+   */
+  void
+  loadPkcs8Base64(std::istream& is, PasswordCallback pwCallback = nullptr);
+
+  /**
+   * @brief Save the private key in PKCS#1 format into a stream @p os
+   */
+  void
+  savePkcs1(std::ostream& os) const;
+
+  /**
+   * @brief Save the private key in base64-encoded PKCS#1 format into a stream @p os
+   */
+  void
+  savePkcs1Base64(std::ostream& os) const;
+
+  /**
+   * @brief Save the private key in encrypted PKCS#8 format into a stream @p os
+   */
+  void
+  savePkcs8(std::ostream& os, const char* pw, size_t pwLen) const;
+
+  /**
+   * @brief Save the private key in encrypted PKCS#8 format into a stream @p os with passphrase
+   *        obtained from @p pwCallback
+   *
+   * The default password callback is provided by OpenSSL
+   */
+  void
+  savePkcs8(std::ostream& os, PasswordCallback pwCallback = nullptr) const;
+
+  /**
+   * @brief Save the private key in base64-encoded encrypted PKCS#8 format into a stream @p os
+   */
+  void
+  savePkcs8Base64(std::ostream& os, const char* pw, size_t pwLen) const;
+
+  /**
+   * @brief Save the private key in base64-encoded encrypted PKCS#8 format into a stream @p os
+   *        with passphrase obtained from @p pwCallback
+   *
+   * The default password callback is provided by OpenSSL
+   */
+  void
+  savePkcs8Base64(std::ostream& os, PasswordCallback pwCallback = nullptr) const;
+
+  /**
+   * @return Public key bits in PKCS#8 format
+   */
+  ConstBufferPtr
+  derivePublicKey() const;
+
+  /**
+   * @return Plain text of @p cipherText decrypted using the private key.
+   *
+   * Only RSA encryption is supported for now.
+   */
+  ConstBufferPtr
+  decrypt(const uint8_t* cipherText, size_t cipherLen) const;
+
+private:
+  /**
+   * @return A pointer to an EVP_PKEY instance.
+   *
+   * One need to explicitly cast the return value to EVP_PKEY*.
+   */
+  void*
+  getEvpPkey() const;
+
+private:
+  ConstBufferPtr
+  toPkcs1() const;
+
+  ConstBufferPtr
+  toPkcs8(const char* pw, size_t pwLen) const;
+
+  ConstBufferPtr
+  toPkcs8(PasswordCallback pwCallback = nullptr) const;
+
+  ConstBufferPtr
+  rsaDecrypt(const uint8_t* cipherText, size_t cipherLen) const;
+
+private:
+  class Impl;
+  unique_ptr<Impl> m_impl;
+};
+
+/**
+ * @brief generate a private key according to @p keyParams.
+ *
+ * @note the public key can be derived from the private key
+ *
+ * @throw std::argument_error if the key type is not supported
+ * @throw std::runtime_error when failing to generate the key
+ */
+unique_ptr<PrivateKey>
+generatePrivateKey(const KeyParams& keyParams);
+
+} // namespace transform
+} // namespace security
+} // namespace ndn
+
+#endif // NDN_CXX_SECURITY_TRANSFORM_PRIVATE_KEY_HPP