diff --git a/src/security/validator.hpp b/src/security/validator.hpp
new file mode 100644
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--- /dev/null
+++ b/src/security/validator.hpp
@@ -0,0 +1,157 @@
+/* -*- 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>
+ * @author: Jeff Thompson <jefft0@remap.ucla.edu>
+ * See COPYING for copyright and distribution information.
+ */
+
+#ifndef NDN_VALIDATOR_HPP
+#define NDN_VALIDATOR_HPP
+
+#include "../data.hpp"
+#include "../face.hpp"
+#include "public-key.hpp"
+#include "signature-sha256-with-rsa.hpp"
+#include "validation-request.hpp"
+
+namespace ndn {
+/**
+ * Validator is one of the main classes of the security library.
+ *
+ * The Validator class provides the interfaces for packet validation.
+ */
+class Validator {
+public:
+  struct Error : public std::runtime_error { Error(const std::string &what) : std::runtime_error(what) {} };
+
+  static const shared_ptr<Face> DefaultFace;
+
+  Validator (shared_ptr<Face> face = DefaultFace);
+
+  /**
+   * @brief Validate Data and call either onValidated or onValidationFailed. 
+   * 
+   * @param data The Data with the signature to check.
+   * @param onValidated If the Data is validated, this calls onValidated(data).
+   * @param onValidationFailed If the Data validation fails, this calls onValidationFailed(data).
+   */
+  void
+  validate (const shared_ptr<const Data> &data, const OnDataValidated &onValidated, const OnDataValidationFailed &onValidationFailed)
+  { validate (data, onValidated, onValidationFailed, 0); }
+
+  /**
+   * @brief Validate Interest and call either onValidated or onValidationFailed. 
+   * 
+   * @param interest The Interest with the signature to check.
+   * @param onValidated If the Interest is validated, this calls onValidated(interest).
+   * @param onValidationFailed If the Interest validation fails, this calls onValidationFailed(interest).
+   */
+  void
+  validate (const shared_ptr<const Interest> &interest, const OnInterestValidated &onValidated, const OnInterestValidationFailed &onValidationFailed)
+  { validate (interest, onValidated, onValidationFailed, 0); }
+
+  /*****************************************
+   *      verifySignature method set       *
+   *****************************************/
+
+  /// @brief Verify the data using the publicKey.
+  static bool
+  verifySignature (const Data &data, const PublicKey &publicKey);
+
+  /// @brief Verify the signed Interest using the publicKey.
+  static bool
+  verifySignature (const Interest &interest, const PublicKey &publicKey);
+
+  /// @brief Verify the blob using the publicKey against the signature.
+  static bool
+  verifySignature (const Buffer &blob, const Signature &sig, const PublicKey &publicKey);
+
+  /// @brief Verify the data using the publicKey against the SHA256-RSA signature.
+  static bool
+  verifySignature (const Data& data, const SignatureSha256WithRsa& sig, const PublicKey& publicKey);
+
+  /// @brief Verify the blob using the publicKey against the SHA256-RSA signature.
+  static bool
+  verifySignature (const Buffer &blob, const SignatureSha256WithRsa &sig, const PublicKey &publicKey);
+  
+  /// @brief Verify the blob using the publicKey against the SHA256-RSA signature.
+  static bool
+  verifySignature (const uint8_t* buf, const size_t size, const SignatureSha256WithRsa &sig, const PublicKey &publicKey);
+
+protected:
+  /**
+   * @brief Check the Data against validation policy and return the next validation step if necessary.
+   *
+   * If there is no next validation step, that validation MUST have been done.
+   * i.e., either onValidated or onValidationFailed callback is invoked.
+   *
+   * @param data The Data to check.
+   * @param stepCount The number of validation steps that have been done, used to track the validation progress.
+   * @param onDataValidated If the Data is validated, this calls onValidated(data).
+   * @param onDataValidationFailed If the Data validation fails, this calls onValidationFailed(data).
+   * @param nextSteps On return, contains the next validation step.
+   */
+  virtual void
+  checkPolicy (const shared_ptr<const Data> &data, 
+               int stepCount, 
+               const OnDataValidated &onValidated, 
+               const OnDataValidationFailed &onValidationFailed,
+               std::vector<shared_ptr<ValidationRequest> > &nextSteps)
+  { onValidationFailed(data); }
+
+  /**
+   * @brief Check the Interest against validation policy and return the next validation step if necessary.
+   *
+   * If there is no next validation step, that validation MUST have been done.
+   * i.e., either onValidated or onValidationFailed callback is invoked.
+   *
+   * @param data The Interest to check.
+   * @param stepCount The number of validation steps that have been done, used to track the validation progress.
+   * @param OnInterestValidated If the Interest is validated, this calls onValidated(data).
+   * @param OnInterestValidationFailed If the Interest validation fails, this calls onValidationFailed(data).
+   * @return the indication of next validation step, null if there is no further step.
+   */
+  virtual void
+  checkPolicy (const shared_ptr<const Interest> &interest, 
+               int stepCount, 
+               const OnInterestValidated &onValidated, 
+               const OnInterestValidationFailed &onValidationFailed,
+               std::vector<shared_ptr<ValidationRequest> > &nextSteps)
+  { onValidationFailed(interest); }
+
+private:
+  typedef function< void () > OnFailure;
+  
+  /// @brief Process the received certificate.
+  void
+  onData (const shared_ptr<const Interest> &interest, 
+          const shared_ptr<const Data> &data, 
+          shared_ptr<ValidationRequest> nextStep);
+  
+  /// @brief Re-express the interest if it times out.
+  void
+  onTimeout (const shared_ptr<const Interest> &interest, 
+             int retry, 
+             const OnFailure &onFailure, 
+             shared_ptr<ValidationRequest> nextStep);
+
+  void
+  validate (const shared_ptr<const Data> &data, 
+            const OnDataValidated &onValidated, 
+            const OnDataValidationFailed &onValidationFailed, 
+            int stepCount);
+
+  void
+  validate (const shared_ptr<const Interest> &interest, 
+            const OnInterestValidated &onValidated, 
+            const OnInterestValidationFailed &onValidationFailed, 
+            int stepCount);
+
+protected:
+  shared_ptr<Face> m_face;
+};
+
+}
+
+#endif