diff --git a/src/security/v2/validator.hpp b/src/security/v2/validator.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_V2_VALIDATOR_HPP
+#define NDN_SECURITY_V2_VALIDATOR_HPP
+
+#include "certificate.hpp"
+#include "certificate-cache.hpp"
+#include "certificate-request.hpp"
+#include "trust-anchor-container.hpp"
+#include "validation-callback.hpp"
+#include "validation-policy.hpp"
+#include "validation-state.hpp"
+
+namespace ndn {
+
+class Face;
+
+namespace lp {
+class Nack;
+} // namespace lp
+
+namespace security {
+namespace v2 {
+
+/**
+ * @brief Interface for validating data and interest packets.
+ *
+ * Every time a validation process initiated, it creates a ValidationState that exist until
+ * validation finishes with either success or failure.  This state serves several purposes:
+ * - record Interest or Data packet being validated
+ * - record failure callback
+ * - record certificates in the certification chain for the Interest or Data packet being validated
+ * - record names of the requested certificates to detect loops in the certificate chain
+ * - keep track of the validation chain size (aka validation "depth")
+ *
+ * During validation, policy can augment validation state with policy- and fetcher-specific
+ * information using ndn::Tag's.
+ *
+ * A validator has a trust anchor cache to save static and dynamic trust anchors, a verified
+ * certificate cache for saving certificates that are already verified and an unverified
+ * certificate cache for saving prefetched but not yet verified certificates.
+ *
+ * @todo Limit the maximum time the validation process is allowed to run before declaring failure
+ * @todo Ability to customize maximum lifetime for trusted and untrusted certificate caches.
+ *       Current implementation hard-codes them to be 1 hour and 5 minutes.
+ */
+class Validator : noncopyable
+{
+public:
+  /**
+   * @brief Validator constructor.
+   *
+   * @param policy Validation policy to be associated with the validator
+   * @param face   Face for fetching certificates from network.  If provided, the Validator
+   *               operates in online mode; otherwise, the Validator operates in offline mode.
+   */
+  explicit
+  Validator(unique_ptr<ValidationPolicy> policy, Face* face = nullptr);
+
+  ~Validator();
+
+  /**
+   * @brief Set the maximum depth of the certificate chain
+   */
+  void
+  setMaxDepth(size_t depth);
+
+  /**
+   * @return The maximum depth of the certificate chain
+   */
+  size_t
+  getMaxDepth() const;
+
+  /**
+   * @brief Asynchronously validate @p data
+   *
+   * @note @p successCb and @p failureCb must not be nullptr
+   */
+  void
+  validate(const Data& data,
+           const DataValidationSuccessCallback& successCb,
+           const DataValidationFailureCallback& failureCb);
+
+  /**
+   * @brief Asynchronously validate @p interest
+   *
+   * @note @p successCb and @p failureCb must not be nullptr
+   */
+  void
+  validate(const Interest& interest,
+           const InterestValidationSuccessCallback& successCb,
+           const InterestValidationFailureCallback& failureCb);
+
+public: // anchor management
+  /**
+   * @brief load static trust anchor.
+   *
+   * Static trust anchors are permanently associated with the validator and never expire.
+   *
+   * @param groupId  Certificate group id.
+   * @param cert     Certificate to load as a trust anchor.
+   */
+  void
+  loadAnchor(const std::string& groupId, Certificate&& cert);
+
+  /**
+   * @brief load dynamic trust anchors.
+   *
+   * Dynamic trust anchors are associated with the validator for as long as the underlying
+   * trust anchor file (set of files) exist(s).
+   *
+   * @param groupId          Certificate group id, must not be empty.
+   * @param certfilePath     Specifies the path to load the trust anchors.
+   * @param refreshPeriod    Refresh period for the trust anchors, must be positive.
+   * @param isDir            Tells whether the path is a directory or a single file.
+   */
+  void
+  loadAnchor(const std::string& groupId, const std::string& certfilePath,
+             time::nanoseconds refreshPeriod, bool isDir = false);
+
+  /**
+   * @brief Cache verified @p cert a period of time (1 hour)
+   *
+   * @todo Add ability to customize time period
+   */
+  void
+  cacheVerifiedCertificate(Certificate&& cert);
+
+  /**
+   * @brief Cache unverified @p cert for a period of time (5 minutes)
+   *
+   * @todo Add ability to customize time period
+   */
+  void
+  cacheUnverifiedCertificate(Certificate&& cert);
+
+  /**
+   * @return Trust anchor container
+   */
+  const TrustAnchorContainer&
+  getTrustAnchors() const;
+
+  /**
+   * @return Verified certificate cache
+   */
+  const CertificateCache&
+  getVerifiedCertificateCache() const;
+
+  /**
+   * @return Unverified certificate cache
+   */
+  const CertificateCache&
+  getUnverifiedCertificateCache() const;
+
+  /**
+   * @brief Check if certificate with @p certName exists in verified or unverified cache
+   */
+  bool
+  isCertificateCached(const Name& certName) const;
+
+private: // Common validator operations
+  /**
+   * @brief Recursive validation of the certificate in the certification chain
+   *
+   * @param cert   The certificate to check.
+   * @param state  The current validation state.
+   */
+  void
+  validate(const Certificate& cert, const shared_ptr<ValidationState>& state);
+
+  /**
+   * @brief Request certificate for further validation.
+   *
+   * @param certRequest  Certificate request.
+   * @param state        The current validation state.
+   */
+  void
+  requestCertificate(const shared_ptr<CertificateRequest>& certRequest,
+                     const shared_ptr<ValidationState>& state);
+
+  /**
+   * @brief Find trusted certificate among trust anchors and verified certificates.
+   *
+   * @param interestForCertificate Interest for certificate
+   * @param state                  The current validation state.
+   *
+   * @return found certificate, nullptr if not found.
+   *
+   * @note The returned pointer may get invalidated after next findTrustedCert call.
+   */
+  const Certificate*
+  findTrustedCert(const Interest& interestForCertificate,
+                  const shared_ptr<ValidationState>& state);
+
+  /**
+   * @brief fetch certificate from network based on certificate request.
+   *
+   * @param certRequest Certificate request.
+   * @param state       The current validation state.
+   */
+  void
+  fetchCertificateFromNetwork(const shared_ptr<CertificateRequest>& certRequest,
+                              const shared_ptr<ValidationState>& state);
+
+  /**
+   * @brief Callback invoked when certificated is retrieved.
+   *
+   * @param data        Retrieved certificate.
+   * @param certRequest Certificate request.
+   * @param state       The current validation state.
+   * @param isFromNetwork Flag to indicate that the data packet is retrieved (to avoid re-caching).
+   */
+  void
+  dataCallback(const Data& data,
+               const shared_ptr<CertificateRequest>& certRequest,
+               const shared_ptr<ValidationState>& state,
+               bool isFromNetwork = true);
+
+  /**
+   * @brief Callback invoked when interest for fetching certificate gets NACKed.
+   *
+   * It will retry for pre-configured amount of retries.
+   *
+   * @param nack        Received NACK
+   * @param certRequest Certificate request.
+   * @param state       The current validation state.
+   */
+  void
+  nackCallback(const lp::Nack& nack, const shared_ptr<CertificateRequest>& certRequest,
+               const shared_ptr<ValidationState>& state);
+
+  /**
+   * @brief Callback invoked when interest for fetching certificate times out.
+   *
+   * It will retry for pre-configured amount of retries.
+   *
+   * @param certRequest Certificate request.
+   * @param state       The current validation state.
+   */
+  void
+  timeoutCallback(const shared_ptr<CertificateRequest>& certRequest,
+                  const shared_ptr<ValidationState>& state);
+
+private:
+  unique_ptr<ValidationPolicy> m_policy;
+  Face* m_face;
+  TrustAnchorContainer m_trustAnchors;
+  CertificateCache m_verifiedCertificateCache;
+  CertificateCache m_unverifiedCertificateCache;
+  size_t m_maxDepth;
+};
+
+} // namespace v2
+} // namespace security
+} // namespace ndn
+
+#endif // NDN_SECURITY_V2_VALIDATOR_HPP